diff --git a/phpseclib/Common/Functions/Strings.php b/phpseclib/Common/Functions/Strings.php
new file mode 100644
index 00000000..235f8981
--- /dev/null
+++ b/phpseclib/Common/Functions/Strings.php
@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * Common String Functions
+ *
+ * PHP version 5
+ *
+ * @category  Common
+ * @package   Functions\Strings
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @copyright 2016 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Common\Functions;
+
+/**
+ * Common String Functions
+ *
+ * @package Functions\Strings
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+class Strings
+{
+    /**
+     * String Shift
+     *
+     * Inspired by array_shift
+     *
+     * @param string $string
+     * @param int $index
+     * @access private
+     * @return string
+     */
+    static function shift(&$string, $index = 1)
+    {
+        $substr = substr($string, 0, $index);
+        $string = substr($string, $index);
+        return $substr;
+    }
+}
diff --git a/phpseclib/Crypt/Blowfish.php b/phpseclib/Crypt/Blowfish.php
index 3500df59..a94367eb 100644
--- a/phpseclib/Crypt/Blowfish.php
+++ b/phpseclib/Crypt/Blowfish.php
@@ -37,6 +37,8 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\BlockCipher;
+
 /**
  * Pure-PHP implementation of Blowfish.
  *
@@ -45,12 +47,12 @@ namespace phpseclib\Crypt;
  * @author  Hans-Juergen Petrich <petrich@tronic-media.com>
  * @access  public
  */
-class Blowfish extends Base
+class Blowfish extends BlockCipher
 {
     /**
      * Block Length of the cipher
      *
-     * @see \phpseclib\Crypt\Base::block_size
+     * @see \phpseclib\Crypt\Common\SymmetricKey::block_size
      * @var int
      * @access private
      */
@@ -59,7 +61,7 @@ class Blowfish extends Base
     /**
      * The mcrypt specific name of the cipher
      *
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
      * @var string
      * @access private
      */
@@ -68,7 +70,7 @@ class Blowfish extends Base
     /**
      * Optimizing value while CFB-encrypting
      *
-     * @see \phpseclib\Crypt\Base::cfb_init_len
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cfb_init_len
      * @var int
      * @access private
      */
@@ -273,7 +275,7 @@ class Blowfish extends Base
     /**
      * The Key Length (in bytes)
      *
-     * @see \phpseclib\Crypt\Base::setKeyLength()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setKeyLength()
      * @var int
      * @access private
      * @internal The max value is 256 / 8 = 32, the min value is 128 / 8 = 16.  Exists in conjunction with $Nk
@@ -321,9 +323,9 @@ class Blowfish extends Base
     /**
      * Test for engine validity
      *
-     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Base::isValidEngine()
+     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      *
-     * @see \phpseclib\Crypt\Base::isValidEngine()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      * @param int $engine
      * @access public
      * @return bool
@@ -344,7 +346,7 @@ class Blowfish extends Base
     /**
      * Setup the key (expansion)
      *
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
@@ -471,7 +473,7 @@ class Blowfish extends Base
     /**
      * Setup the performance-optimized function for de/encrypt()
      *
-     * @see \phpseclib\Crypt\Base::_setupInlineCrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupInlineCrypt()
      * @access private
      */
     function _setupInlineCrypt()
diff --git a/phpseclib/Crypt/Common/BlockCipher.php b/phpseclib/Crypt/Common/BlockCipher.php
new file mode 100644
index 00000000..01cceb0b
--- /dev/null
+++ b/phpseclib/Crypt/Common/BlockCipher.php
@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * Base Class for all block ciphers
+ *
+ * PHP version 5
+ *
+ * @category  Crypt
+ * @package   BlockCipher
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @author    Hans-Juergen Petrich <petrich@tronic-media.com>
+ * @copyright 2007 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Crypt\Common;
+
+/**
+ * Base Class for all block cipher classes
+ *
+ * @package BlockCipher
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+abstract class BlockCipher extends SymmetricKey
+{
+}
diff --git a/phpseclib/Crypt/Common/StreamCipher.php b/phpseclib/Crypt/Common/StreamCipher.php
new file mode 100644
index 00000000..01b055b2
--- /dev/null
+++ b/phpseclib/Crypt/Common/StreamCipher.php
@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * Base Class for all stream ciphers
+ *
+ * PHP version 5
+ *
+ * @category  Crypt
+ * @package   StreamCipher
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @author    Hans-Juergen Petrich <petrich@tronic-media.com>
+ * @copyright 2007 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Crypt\Common;
+
+/**
+ * Base Class for all stream cipher classes
+ *
+ * @package StreamCipher
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+abstract class StreamCipher extends SymmetricKey
+{
+}
diff --git a/phpseclib/Crypt/Base.php b/phpseclib/Crypt/Common/SymmetricKey.php
similarity index 97%
rename from phpseclib/Crypt/Base.php
rename to phpseclib/Crypt/Common/SymmetricKey.php
index e3cc7b87..9fd0476f 100644
--- a/phpseclib/Crypt/Base.php
+++ b/phpseclib/Crypt/Common/SymmetricKey.php
@@ -8,7 +8,7 @@
  * Internally for phpseclib developers:
  *  If you plan to add a new cipher class, please note following rules:
  *
- *  - The new \phpseclib\Crypt\* cipher class should extend \phpseclib\Crypt\Base
+ *  - The new \phpseclib\Crypt\* cipher class should extend \phpseclib\Crypt\Common\SymmetricKey
  *
  *  - Following methods are then required to be overridden/overloaded:
  *
@@ -20,7 +20,7 @@
  *
  *  - All other methods are optional to be overridden/overloaded
  *
- *  - Look at the source code of the current ciphers how they extend \phpseclib\Crypt\Base
+ *  - Look at the source code of the current ciphers how they extend \phpseclib\Crypt\Common\SymmetricKey
  *    and take one of them as a start up for the new cipher class.
  *
  *  - Please read all the other comments/notes/hints here also for each class var/method
@@ -34,7 +34,10 @@
  * @link      http://phpseclib.sourceforge.net
  */
 
-namespace phpseclib\Crypt;
+namespace phpseclib\Crypt\Common;
+
+use phpseclib\Crypt\Hash;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Base Class for all \phpseclib\Crypt\* cipher classes
@@ -43,12 +46,12 @@ namespace phpseclib\Crypt;
  * @author  Jim Wigginton <terrafrost@php.net>
  * @author  Hans-Juergen Petrich <petrich@tronic-media.com>
  */
-abstract class Base
+abstract class SymmetricKey
 {
     /**#@+
      * @access public
-     * @see \phpseclib\Crypt\Base::encrypt()
-     * @see \phpseclib\Crypt\Base::decrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::encrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::decrypt()
      */
     /**
      * Encrypt / decrypt using the Counter mode.
@@ -91,7 +94,7 @@ abstract class Base
     /**
      * Whirlpool available flag
      *
-     * @see \phpseclib\Crypt\Base::_hashInlineCryptFunction()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_hashInlineCryptFunction()
      * @var bool
      * @access private
      */
@@ -99,7 +102,7 @@ abstract class Base
 
     /**#@+
      * @access private
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      */
     /**
      * Base value for the internal implementation $engine switch
@@ -901,7 +904,7 @@ abstract class Base
                             $buffer['ciphertext'].= $this->_encryptBlock($xor);
                         }
                         $this->_increment_str($xor);
-                        $key = $this->_string_shift($buffer['ciphertext'], $block_size);
+                        $key = Strings::shift($buffer['ciphertext'], $block_size);
                         $ciphertext.= $block ^ $key;
                     }
                 } else {
@@ -970,7 +973,7 @@ abstract class Base
                             $xor = $this->_encryptBlock($xor);
                             $buffer['xor'].= $xor;
                         }
-                        $key = $this->_string_shift($buffer['xor'], $block_size);
+                        $key = Strings::shift($buffer['xor'], $block_size);
                         $ciphertext.= $block ^ $key;
                     }
                 } else {
@@ -1194,7 +1197,7 @@ abstract class Base
                             $buffer['ciphertext'].= $this->_encryptBlock($xor);
                             $this->_increment_str($xor);
                         }
-                        $key = $this->_string_shift($buffer['ciphertext'], $block_size);
+                        $key = Strings::shift($buffer['ciphertext'], $block_size);
                         $plaintext.= $block ^ $key;
                     }
                 } else {
@@ -1262,7 +1265,7 @@ abstract class Base
                             $xor = $this->_encryptBlock($xor);
                             $buffer['xor'].= $xor;
                         }
-                        $key = $this->_string_shift($buffer['xor'], $block_size);
+                        $key = Strings::shift($buffer['xor'], $block_size);
                         $plaintext.= $block ^ $key;
                     }
                 } else {
@@ -1306,8 +1309,8 @@ abstract class Base
      * OpenSSL CTR Processor
      *
      * PHP's OpenSSL bindings do not operate in continuous mode so we'll wrap around it. Since the keystream
-     * for CTR is the same for both encrypting and decrypting this function is re-used by both Base::encrypt()
-     * and Base::decrypt(). Also, OpenSSL doesn't implement CTR for all of it's symmetric ciphers so this
+     * for CTR is the same for both encrypting and decrypting this function is re-used by both SymmetricKey::encrypt()
+     * and SymmetricKey::decrypt(). Also, OpenSSL doesn't implement CTR for all of it's symmetric ciphers so this
      * function will emulate CTR with ECB when necesary.
      *
      * @see self::encrypt()
@@ -1336,7 +1339,7 @@ abstract class Base
                         $buffer['ciphertext'].= $result;
                     }
                     $this->_increment_str($xor);
-                    $otp = $this->_string_shift($buffer['ciphertext'], $block_size);
+                    $otp = Strings::shift($buffer['ciphertext'], $block_size);
                     $ciphertext.= $block ^ $otp;
                 }
             } else {
@@ -1359,7 +1362,7 @@ abstract class Base
         }
 
         if (strlen($buffer['ciphertext'])) {
-            $ciphertext = $plaintext ^ $this->_string_shift($buffer['ciphertext'], strlen($plaintext));
+            $ciphertext = $plaintext ^ Strings::shift($buffer['ciphertext'], strlen($plaintext));
             $plaintext = substr($plaintext, strlen($ciphertext));
 
             if (!strlen($plaintext)) {
@@ -1401,8 +1404,8 @@ abstract class Base
      * OpenSSL OFB Processor
      *
      * PHP's OpenSSL bindings do not operate in continuous mode so we'll wrap around it. Since the keystream
-     * for OFB is the same for both encrypting and decrypting this function is re-used by both Base::encrypt()
-     * and Base::decrypt().
+     * for OFB is the same for both encrypting and decrypting this function is re-used by both SymmetricKey::encrypt()
+     * and SymmetricKey::decrypt().
      *
      * @see self::encrypt()
      * @see self::decrypt()
@@ -1435,7 +1438,7 @@ abstract class Base
                 if ($this->continuousBuffer) {
                     $encryptIV = $xor;
                 }
-                $ciphertext.= $this->_string_shift($xor, $overflow) ^ substr($plaintext, -$overflow);
+                $ciphertext.= Strings::shift($xor, $overflow) ^ substr($plaintext, -$overflow);
                 if ($this->continuousBuffer) {
                     $buffer['xor'] = $xor;
                 }
@@ -1640,11 +1643,11 @@ abstract class Base
      *
      * Currently, $engine could be:
      *
-     * - \phpseclib\Crypt\Base::ENGINE_OPENSSL  [very fast]
+     * - \phpseclib\Crypt\Common\SymmetricKey::ENGINE_OPENSSL  [very fast]
      *
-     * - \phpseclib\Crypt\Base::ENGINE_MCRYPT   [fast]
+     * - \phpseclib\Crypt\Common\SymmetricKey::ENGINE_MCRYPT   [fast]
      *
-     * - \phpseclib\Crypt\Base::ENGINE_INTERNAL [slow]
+     * - \phpseclib\Crypt\Common\SymmetricKey::ENGINE_INTERNAL [slow]
      *
      * If the preferred crypt engine is not available the fastest available one will be used
      *
@@ -1924,23 +1927,6 @@ abstract class Base
         $this->encryptIV = $this->decryptIV = $this->iv;
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @access private
-     * @return string
-     */
-    function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * String Pop
      *
@@ -2057,7 +2043,7 @@ abstract class Base
      */
     function _setupInlineCrypt()
     {
-        // If, for any reason, an extending \phpseclib\Crypt\Base() \phpseclib\Crypt\* class
+        // If, for any reason, an extending \phpseclib\Crypt\Common\SymmetricKey() \phpseclib\Crypt\* class
         // not using inline crypting then it must be ensured that: $this->use_inline_crypt = false
         // ie in the class var declaration of $use_inline_crypt in general for the \phpseclib\Crypt\* class,
         // in the constructor at object instance-time
@@ -2236,7 +2222,7 @@ abstract class Base
                                 $self->_increment_str($_xor);
                                 $_buffer["ciphertext"].= $in;
                             }
-                            $_key = $self->_string_shift($_buffer["ciphertext"], '.$block_size.');
+                            $_key = \phpseclib\Common\Functions\Strings::shift($_buffer["ciphertext"], '.$block_size.');
                             $_ciphertext.= $_block ^ $_key;
                         }
                     } else {
@@ -2274,7 +2260,7 @@ abstract class Base
                                 $self->_increment_str($_xor);
                                 $_buffer["ciphertext"].= $in;
                             }
-                            $_key = $self->_string_shift($_buffer["ciphertext"], '.$block_size.');
+                            $_key = \phpseclib\Common\Functions\Strings::shift($_buffer["ciphertext"], '.$block_size.');
                             $_plaintext.= $_block ^ $_key;
                         }
                     } else {
@@ -2412,7 +2398,7 @@ abstract class Base
                                 $_xor = $in;
                                 $_buffer["xor"].= $_xor;
                             }
-                            $_key = $self->_string_shift($_buffer["xor"], '.$block_size.');
+                            $_key = \phpseclib\Common\Functions\Strings::shift($_buffer["xor"], '.$block_size.');
                             $_ciphertext.= $_block ^ $_key;
                         }
                     } else {
@@ -2448,7 +2434,7 @@ abstract class Base
                                 $_xor = $in;
                                 $_buffer["xor"].= $_xor;
                             }
-                            $_key = $self->_string_shift($_buffer["xor"], '.$block_size.');
+                            $_key = \phpseclib\Common\Functions\Strings::shift($_buffer["xor"], '.$block_size.');
                             $_plaintext.= $_block ^ $_key;
                         }
                     } else {
diff --git a/phpseclib/Crypt/DES.php b/phpseclib/Crypt/DES.php
index 14273d28..31df0ebd 100644
--- a/phpseclib/Crypt/DES.php
+++ b/phpseclib/Crypt/DES.php
@@ -42,6 +42,8 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\BlockCipher;
+
 /**
  * Pure-PHP implementation of DES.
  *
@@ -49,7 +51,7 @@ namespace phpseclib\Crypt;
  * @author  Jim Wigginton <terrafrost@php.net>
  * @access  public
  */
-class DES extends Base
+class DES extends BlockCipher
 {
     /**#@+
      * @access private
@@ -69,7 +71,7 @@ class DES extends Base
     /**
      * Block Length of the cipher
      *
-     * @see \phpseclib\Crypt\Base::block_size
+     * @see \phpseclib\Crypt\Common\SymmetricKey::block_size
      * @var int
      * @access private
      */
@@ -78,7 +80,7 @@ class DES extends Base
     /**
      * Key Length (in bytes)
      *
-     * @see \phpseclib\Crypt\Base::setKeyLength()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setKeyLength()
      * @var int
      * @access private
      */
@@ -87,7 +89,7 @@ class DES extends Base
     /**
      * The mcrypt specific name of the cipher
      *
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
      * @var string
      * @access private
      */
@@ -96,7 +98,7 @@ class DES extends Base
     /**
      * The OpenSSL names of the cipher / modes
      *
-     * @see \phpseclib\Crypt\Base::openssl_mode_names
+     * @see \phpseclib\Crypt\Common\SymmetricKey::openssl_mode_names
      * @var array
      * @access private
      */
@@ -111,7 +113,7 @@ class DES extends Base
     /**
      * Optimizing value while CFB-encrypting
      *
-     * @see \phpseclib\Crypt\Base::cfb_init_len
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cfb_init_len
      * @var int
      * @access private
      */
@@ -597,9 +599,9 @@ class DES extends Base
     /**
      * Test for engine validity
      *
-     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Base::isValidEngine()
+     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      *
-     * @see \phpseclib\Crypt\Base::isValidEngine()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      * @param int $engine
      * @access public
      * @return bool
@@ -623,7 +625,7 @@ class DES extends Base
      *
      * DES also requires that every eighth bit be a parity bit, however, we'll ignore that.
      *
-     * @see \phpseclib\Crypt\Base::setKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setKey()
      * @access public
      * @param string $key
      */
@@ -640,8 +642,8 @@ class DES extends Base
     /**
      * Encrypts a block
      *
-     * @see \phpseclib\Crypt\Base::_encryptBlock()
-     * @see \phpseclib\Crypt\Base::encrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_encryptBlock()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::encrypt()
      * @see self::encrypt()
      * @access private
      * @param string $in
@@ -655,8 +657,8 @@ class DES extends Base
     /**
      * Decrypts a block
      *
-     * @see \phpseclib\Crypt\Base::_decryptBlock()
-     * @see \phpseclib\Crypt\Base::decrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_decryptBlock()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::decrypt()
      * @see self::decrypt()
      * @access private
      * @param string $in
@@ -759,7 +761,7 @@ class DES extends Base
     /**
      * Creates the key schedule
      *
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
@@ -1294,7 +1296,7 @@ class DES extends Base
     /**
      * Setup the performance-optimized function for de/encrypt()
      *
-     * @see \phpseclib\Crypt\Base::_setupInlineCrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupInlineCrypt()
      * @access private
      */
     function _setupInlineCrypt()
diff --git a/phpseclib/Crypt/Hash.php b/phpseclib/Crypt/Hash.php
index be48a14a..0476ca8b 100644
--- a/phpseclib/Crypt/Hash.php
+++ b/phpseclib/Crypt/Hash.php
@@ -35,6 +35,7 @@ namespace phpseclib\Crypt;
 
 use phpseclib\Math\BigInteger;
 use phpseclib\Exception\UnsupportedAlgorithmException;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * @package Hash
@@ -327,7 +328,7 @@ class Hash
         foreach ($chunks as $chunk) {
             $w = array();
             for ($i = 0; $i < 16; $i++) {
-                $temp = new BigInteger(self::_string_shift($chunk, 8), 256);
+                $temp = new BigInteger(Strings::shift($chunk, 8), 256);
                 $temp->setPrecision(64);
                 $w[] = $temp;
             }
@@ -429,21 +430,4 @@ class Hash
 
         return $temp;
     }
-
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    static function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
 }
diff --git a/phpseclib/Crypt/RC2.php b/phpseclib/Crypt/RC2.php
index 648cf96a..172b8d85 100644
--- a/phpseclib/Crypt/RC2.php
+++ b/phpseclib/Crypt/RC2.php
@@ -35,18 +35,20 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\BlockCipher;
+
 /**
  * Pure-PHP implementation of RC2.
  *
  * @package RC2
  * @access  public
  */
-class RC2 extends Base
+class RC2 extends BlockCipher
 {
     /**
      * Block Length of the cipher
      *
-     * @see \phpseclib\Crypt\Base::block_size
+     * @see \phpseclib\Crypt\Common\SymmetricKey::block_size
      * @var int
      * @access private
      */
@@ -55,7 +57,7 @@ class RC2 extends Base
     /**
      * The Key
      *
-     * @see \phpseclib\Crypt\Base::key
+     * @see \phpseclib\Crypt\Common\SymmetricKey::key
      * @see self::setKey()
      * @var string
      * @access private
@@ -65,7 +67,7 @@ class RC2 extends Base
     /**
      * The Original (unpadded) Key
      *
-     * @see \phpseclib\Crypt\Base::key
+     * @see \phpseclib\Crypt\Common\SymmetricKey::key
      * @see self::setKey()
      * @see self::encrypt()
      * @see self::decrypt()
@@ -77,7 +79,7 @@ class RC2 extends Base
     /**
      * Don't truncate / null pad key
      *
-     * @see \phpseclib\Crypt\Base::_clearBuffers()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_clearBuffers()
      * @var bool
      * @access private
      */
@@ -95,7 +97,7 @@ class RC2 extends Base
     /**
      * The mcrypt specific name of the cipher
      *
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
      * @var string
      * @access private
      */
@@ -104,7 +106,7 @@ class RC2 extends Base
     /**
      * Optimizing value while CFB-encrypting
      *
-     * @see \phpseclib\Crypt\Base::cfb_init_len
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cfb_init_len
      * @var int
      * @access private
      */
@@ -278,9 +280,9 @@ class RC2 extends Base
     /**
      * Test for engine validity
      *
-     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Base::isValidEngine()
+     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      *
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      * @param int $engine
      * @access public
      * @return bool
@@ -341,7 +343,7 @@ class RC2 extends Base
      * If the key is not explicitly set, it'll be assumed to be a single
      * null byte.
      *
-     * @see \phpseclib\Crypt\Base::setKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setKey()
      * @access public
      * @param string $key
      * @param int $t1 optional Effective key length in bits.
@@ -396,7 +398,7 @@ class RC2 extends Base
     /**
      * Encrypts a message.
      *
-     * Mostly a wrapper for \phpseclib\Crypt\Base::encrypt, with some additional OpenSSL handling code
+     * Mostly a wrapper for \phpseclib\Crypt\Common\SymmetricKey::encrypt, with some additional OpenSSL handling code
      *
      * @see self::decrypt()
      * @access public
@@ -419,7 +421,7 @@ class RC2 extends Base
     /**
      * Decrypts a message.
      *
-     * Mostly a wrapper for \phpseclib\Crypt\Base::decrypt, with some additional OpenSSL handling code
+     * Mostly a wrapper for \phpseclib\Crypt\Common\SymmetricKey::decrypt, with some additional OpenSSL handling code
      *
      * @see self::encrypt()
      * @access public
@@ -442,8 +444,8 @@ class RC2 extends Base
     /**
      * Encrypts a block
      *
-     * @see \phpseclib\Crypt\Base::_encryptBlock()
-     * @see \phpseclib\Crypt\Base::encrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_encryptBlock()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::encrypt()
      * @access private
      * @param string $in
      * @return string
@@ -487,8 +489,8 @@ class RC2 extends Base
     /**
      * Decrypts a block
      *
-     * @see \phpseclib\Crypt\Base::_decryptBlock()
-     * @see \phpseclib\Crypt\Base::decrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_decryptBlock()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::decrypt()
      * @access private
      * @param string $in
      * @return string
@@ -530,9 +532,9 @@ class RC2 extends Base
     }
 
     /**
-     * Setup the \phpseclib\Crypt\Base::ENGINE_MCRYPT $engine
+     * Setup the \phpseclib\Crypt\Common\SymmetricKey::ENGINE_MCRYPT $engine
      *
-     * @see \phpseclib\Crypt\Base::_setupMcrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupMcrypt()
      * @access private
      */
     function _setupMcrypt()
@@ -547,7 +549,7 @@ class RC2 extends Base
     /**
      * Creates the key schedule
      *
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
@@ -568,7 +570,7 @@ class RC2 extends Base
     /**
      * Setup the performance-optimized function for de/encrypt()
      *
-     * @see \phpseclib\Crypt\Base::_setupInlineCrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupInlineCrypt()
      * @access private
      */
     function _setupInlineCrypt()
diff --git a/phpseclib/Crypt/RC4.php b/phpseclib/Crypt/RC4.php
index 3da70b6e..8673d3db 100644
--- a/phpseclib/Crypt/RC4.php
+++ b/phpseclib/Crypt/RC4.php
@@ -44,6 +44,8 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\StreamCipher;
+
 /**
  * Pure-PHP implementation of RC4.
  *
@@ -51,7 +53,7 @@ namespace phpseclib\Crypt;
  * @author  Jim Wigginton <terrafrost@php.net>
  * @access  public
  */
-class RC4 extends Base
+class RC4 extends StreamCipher
 {
     /**#@+
      * @access private
@@ -67,7 +69,7 @@ class RC4 extends Base
      * RC4 is a stream cipher
      * so we the block_size to 0
      *
-     * @see \phpseclib\Crypt\Base::block_size
+     * @see \phpseclib\Crypt\Common\SymmetricKey::block_size
      * @var int
      * @access private
      */
@@ -85,7 +87,7 @@ class RC4 extends Base
     /**
      * The mcrypt specific name of the cipher
      *
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
      * @var string
      * @access private
      */
@@ -94,7 +96,7 @@ class RC4 extends Base
     /**
      * Holds whether performance-optimized $inline_crypt() can/should be used.
      *
-     * @see \phpseclib\Crypt\Base::inline_crypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::inline_crypt
      * @var mixed
      * @access private
      */
@@ -121,21 +123,21 @@ class RC4 extends Base
     /**
      * Default Constructor.
      *
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      * @return \phpseclib\Crypt\RC4
      * @access public
      */
     function __construct()
     {
-        parent::__construct(Base::MODE_STREAM);
+        parent::__construct(self::MODE_STREAM);
     }
 
     /**
      * Test for engine validity
      *
-     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Base::isValidEngine()
+     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      *
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      * @param int $engine
      * @access public
      * @return bool
@@ -143,7 +145,7 @@ class RC4 extends Base
     function isValidEngine($engine)
     {
         switch ($engine) {
-            case Base::ENGINE_OPENSSL:
+            case self::ENGINE_OPENSSL:
                 switch (strlen($this->key)) {
                     case 5:
                         $this->cipher_name_openssl = 'rc4-40';
@@ -215,7 +217,7 @@ class RC4 extends Base
     /**
      * Encrypts a message.
      *
-     * @see \phpseclib\Crypt\Base::decrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::decrypt()
      * @see self::_crypt()
      * @access public
      * @param string $plaintext
@@ -223,7 +225,7 @@ class RC4 extends Base
      */
     function encrypt($plaintext)
     {
-        if ($this->engine != Base::ENGINE_INTERNAL) {
+        if ($this->engine != self::ENGINE_INTERNAL) {
             return parent::encrypt($plaintext);
         }
         return $this->_crypt($plaintext, self::ENCRYPT);
@@ -235,7 +237,7 @@ class RC4 extends Base
      * $this->decrypt($this->encrypt($plaintext)) == $this->encrypt($this->encrypt($plaintext)).
      * At least if the continuous buffer is disabled.
      *
-     * @see \phpseclib\Crypt\Base::encrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::encrypt()
      * @see self::_crypt()
      * @access public
      * @param string $ciphertext
@@ -243,7 +245,7 @@ class RC4 extends Base
      */
     function decrypt($ciphertext)
     {
-        if ($this->engine != Base::ENGINE_INTERNAL) {
+        if ($this->engine != self::ENGINE_INTERNAL) {
             return parent::decrypt($ciphertext);
         }
         return $this->_crypt($ciphertext, self::DECRYPT);
@@ -274,7 +276,7 @@ class RC4 extends Base
     /**
      * Setup the key (expansion)
      *
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
diff --git a/phpseclib/Crypt/RSA.php b/phpseclib/Crypt/RSA.php
index 87a0a6e3..c8294189 100644
--- a/phpseclib/Crypt/RSA.php
+++ b/phpseclib/Crypt/RSA.php
@@ -48,6 +48,7 @@ namespace phpseclib\Crypt;
 use ParagonIE\ConstantTime\Base64;
 use phpseclib\File\ASN1;
 use phpseclib\Math\BigInteger;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Pure-PHP PKCS#1 compliant implementation of RSA.
@@ -1104,10 +1105,10 @@ class RSA
      */
     function _decodeLength(&$string)
     {
-        $length = ord($this->_string_shift($string));
+        $length = ord(Strings::shift($string));
         if ($length & 0x80) { // definite length, long form
             $length&= 0x7F;
-            $temp = $this->_string_shift($string, $length);
+            $temp = Strings::shift($string, $length);
             list(, $length) = unpack('N', substr(str_pad($temp, 4, chr(0), STR_PAD_LEFT), -4));
         }
         return $length;
@@ -1133,23 +1134,6 @@ class RSA
         return pack('Ca*', 0x80 | strlen($temp), $temp);
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * Determines the private key format
      *
@@ -2072,12 +2056,12 @@ class RSA
             return false;
         }
 
-        if ($this->_string_shift($em, 2) != "\0\1") {
+        if (Strings::shift($em, 2) != "\0\1") {
             return false;
         }
 
         $em = ltrim($em, "\xFF");
-        if ($this->_string_shift($em) != "\0") {
+        if (Strings::shift($em) != "\0") {
             return false;
         }
 
diff --git a/phpseclib/Crypt/RSA/MSBLOB.php b/phpseclib/Crypt/RSA/MSBLOB.php
index b99dc2f0..d319a62a 100644
--- a/phpseclib/Crypt/RSA/MSBLOB.php
+++ b/phpseclib/Crypt/RSA/MSBLOB.php
@@ -20,6 +20,7 @@ namespace phpseclib\Crypt\RSA;
 
 use ParagonIE\ConstantTime\Base64;
 use phpseclib\Math\BigInteger;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Microsoft BLOB Formatted RSA Key Handler
@@ -85,7 +86,7 @@ class MSBLOB
 
         // PUBLICKEYSTRUC  publickeystruc
         // https://msdn.microsoft.com/en-us/library/windows/desktop/aa387453(v=vs.85).aspx
-        extract(unpack('atype/aversion/vreserved/Valgo', self::_string_shift($key, 8)));
+        extract(unpack('atype/aversion/vreserved/Valgo', Strings::shift($key, 8)));
         switch (ord($type)) {
             case self::PUBLICKEYBLOB:
             case self::PUBLICKEYBLOBEX:
@@ -112,7 +113,7 @@ class MSBLOB
         // RSAPUBKEY rsapubkey
         // https://msdn.microsoft.com/en-us/library/windows/desktop/aa387685(v=vs.85).aspx
         // could do V for pubexp but that's unsigned 32-bit whereas some PHP installs only do signed 32-bit
-        extract(unpack('Vmagic/Vbitlen/a4pubexp', self::_string_shift($key, 12)));
+        extract(unpack('Vmagic/Vbitlen/a4pubexp', Strings::shift($key, 12)));
         switch ($magic) {
             case self::RSA2:
                 $components['isPublicKey'] = false;
@@ -129,7 +130,7 @@ class MSBLOB
 
         $components[$components['isPublicKey'] ? 'publicExponent' : 'privateExponent'] = new BigInteger(strrev($pubexp), 256);
         // BYTE modulus[rsapubkey.bitlen/8]
-        $components['modulus'] = new BigInteger(strrev(self::_string_shift($key, $bitlen / 8)), 256);
+        $components['modulus'] = new BigInteger(strrev(Strings::shift($key, $bitlen / 8)), 256);
 
         if ($publickey) {
             return $components;
@@ -138,20 +139,20 @@ class MSBLOB
         $components['isPublicKey'] = false;
 
         // BYTE prime1[rsapubkey.bitlen/16]
-        $components['primes'] = array(1 => new BigInteger(strrev(self::_string_shift($key, $bitlen / 16)), 256));
+        $components['primes'] = array(1 => new BigInteger(strrev(Strings::shift($key, $bitlen / 16)), 256));
         // BYTE prime2[rsapubkey.bitlen/16]
-        $components['primes'][] = new BigInteger(strrev(self::_string_shift($key, $bitlen / 16)), 256);
+        $components['primes'][] = new BigInteger(strrev(Strings::shift($key, $bitlen / 16)), 256);
         // BYTE exponent1[rsapubkey.bitlen/16]
-        $components['exponents'] = array(1 => new BigInteger(strrev(self::_string_shift($key, $bitlen / 16)), 256));
+        $components['exponents'] = array(1 => new BigInteger(strrev(Strings::shift($key, $bitlen / 16)), 256));
         // BYTE exponent2[rsapubkey.bitlen/16]
-        $components['exponents'][] = new BigInteger(strrev(self::_string_shift($key, $bitlen / 16)), 256);
+        $components['exponents'][] = new BigInteger(strrev(Strings::shift($key, $bitlen / 16)), 256);
         // BYTE coefficient[rsapubkey.bitlen/16]
-        $components['coefficients'] = array(2 => new BigInteger(strrev(self::_string_shift($key, $bitlen / 16)), 256));
+        $components['coefficients'] = array(2 => new BigInteger(strrev(Strings::shift($key, $bitlen / 16)), 256));
         if (isset($components['privateExponent'])) {
             $components['publicExponent'] = $components['privateExponent'];
         }
         // BYTE privateExponent[rsapubkey.bitlen/8]
-        $components['privateExponent'] = new BigInteger(strrev(self::_string_shift($key, $bitlen / 8)), 256);
+        $components['privateExponent'] = new BigInteger(strrev(Strings::shift($key, $bitlen / 8)), 256);
 
         return $components;
     }
@@ -204,21 +205,4 @@ class MSBLOB
 
         return Base64::encode($key);
     }
-
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    static function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
 }
diff --git a/phpseclib/Crypt/RSA/OpenSSH.php b/phpseclib/Crypt/RSA/OpenSSH.php
index 8cd53282..2f72516a 100644
--- a/phpseclib/Crypt/RSA/OpenSSH.php
+++ b/phpseclib/Crypt/RSA/OpenSSH.php
@@ -18,6 +18,7 @@ namespace phpseclib\Crypt\RSA;
 
 use ParagonIE\ConstantTime\Base64;
 use phpseclib\Math\BigInteger;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * OpenSSH Formatted RSA Key Handler
@@ -73,23 +74,23 @@ class OpenSSH
         if (substr($key, 0, 11) != "\0\0\0\7ssh-rsa") {
             return false;
         }
-        self::_string_shift($key, 11);
+        Strings::shift($key, 11);
         if (strlen($key) <= 4) {
             return false;
         }
-        extract(unpack('Nlength', self::_string_shift($key, 4)));
+        extract(unpack('Nlength', Strings::shift($key, 4)));
         if (strlen($key) <= $length) {
             return false;
         }
-        $publicExponent = new BigInteger(self::_string_shift($key, $length), -256);
+        $publicExponent = new BigInteger(Strings::shift($key, $length), -256);
         if (strlen($key) <= 4) {
             return false;
         }
-        extract(unpack('Nlength', self::_string_shift($key, 4)));
+        extract(unpack('Nlength', Strings::shift($key, 4)));
         if (strlen($key) != $length) {
             return false;
         }
-        $modulus = new BigInteger(self::_string_shift($key, $length), -256);
+        $modulus = new BigInteger(Strings::shift($key, $length), -256);
 
         return array(
             'isPublicKey' => true,
@@ -121,21 +122,4 @@ class OpenSSH
 
         return $RSAPublicKey;
     }
-
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    static function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
 }
diff --git a/phpseclib/Crypt/RSA/PKCS.php b/phpseclib/Crypt/RSA/PKCS.php
index b0ff2559..e8af9a53 100644
--- a/phpseclib/Crypt/RSA/PKCS.php
+++ b/phpseclib/Crypt/RSA/PKCS.php
@@ -16,11 +16,13 @@ namespace phpseclib\Crypt\RSA;
 
 use ParagonIE\ConstantTime\Base64;
 use ParagonIE\ConstantTime\Hex;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\AES;
 use phpseclib\Crypt\Base;
 use phpseclib\Crypt\DES;
 use phpseclib\Crypt\TripleDES;
 use phpseclib\Math\BigInteger;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * PKCS Formatted RSA Key Handler
@@ -94,15 +96,15 @@ abstract class PKCS
     {
         switch ($mode) {
             case 'CBC':
-                return Base::MODE_CBC;
+                return BlockCipher::MODE_CBC;
             case 'ECB':
-                return Base::MODE_ECB;
+                return BlockCipher::MODE_ECB;
             case 'CFB':
-                return Base::MODE_CFB;
+                return BlockCipher::MODE_CFB;
             case 'OFB':
-                return Base::MODE_OFB;
+                return BlockCipher::MODE_OFB;
             case 'CTR':
-                return Base::MODE_CTR;
+                return BlockCipher::MODE_CTR;
         }
         throw new \UnexpectedValueException('Unsupported block cipher mode of operation');
     }
@@ -208,14 +210,14 @@ abstract class PKCS
             }
         }
 
-        if (ord(self::_string_shift($key)) != self::ASN1_SEQUENCE) {
+        if (ord(Strings::shift($key)) != self::ASN1_SEQUENCE) {
             return false;
         }
         if (self::_decodeLength($key) != strlen($key)) {
             return false;
         }
 
-        $tag = ord(self::_string_shift($key));
+        $tag = ord(Strings::shift($key));
         /* intended for keys for which OpenSSL's asn1parse returns the following:
 
             0:d=0  hl=4 l= 631 cons: SEQUENCE
@@ -228,17 +230,17 @@ abstract class PKCS
            ie. PKCS8 keys */
 
         if ($tag == self::ASN1_INTEGER && substr($key, 0, 3) == "\x01\x00\x30") {
-            self::_string_shift($key, 3);
+            Strings::shift($key, 3);
             $tag = self::ASN1_SEQUENCE;
         }
 
         if ($tag == self::ASN1_SEQUENCE) {
-            $temp = self::_string_shift($key, self::_decodeLength($key));
-            if (ord(self::_string_shift($temp)) != self::ASN1_OBJECT) {
+            $temp = Strings::shift($key, self::_decodeLength($key));
+            if (ord(Strings::shift($temp)) != self::ASN1_OBJECT) {
                 return false;
             }
             $length = self::_decodeLength($temp);
-            switch (self::_string_shift($temp, $length)) {
+            switch (Strings::shift($temp, $length)) {
                 case "\x2a\x86\x48\x86\xf7\x0d\x01\x01\x01": // rsaEncryption
                     break;
                 case "\x2a\x86\x48\x86\xf7\x0d\x01\x05\x03": // pbeWithMD5AndDES-CBC
@@ -247,20 +249,20 @@ abstract class PKCS
                            salt OCTET STRING (SIZE(8)),
                            iterationCount INTEGER }
                     */
-                    if (ord(self::_string_shift($temp)) != self::ASN1_SEQUENCE) {
+                    if (ord(Strings::shift($temp)) != self::ASN1_SEQUENCE) {
                         return false;
                     }
                     if (self::_decodeLength($temp) != strlen($temp)) {
                         return false;
                     }
-                    self::_string_shift($temp); // assume it's an octet string
-                    $salt = self::_string_shift($temp, self::_decodeLength($temp));
-                    if (ord(self::_string_shift($temp)) != self::ASN1_INTEGER) {
+                    Strings::shift($temp); // assume it's an octet string
+                    $salt = Strings::shift($temp, self::_decodeLength($temp));
+                    if (ord(Strings::shift($temp)) != self::ASN1_INTEGER) {
                         return false;
                     }
                     self::_decodeLength($temp);
                     list(, $iterationCount) = unpack('N', str_pad($temp, 4, chr(0), STR_PAD_LEFT));
-                    self::_string_shift($key); // assume it's an octet string
+                    Strings::shift($key); // assume it's an octet string
                     $length = self::_decodeLength($key);
                     if (strlen($key) != $length) {
                         return false;
@@ -283,82 +285,82 @@ abstract class PKCS
                 6:d=2  hl=2 l=   9 prim:   OBJECT            :rsaEncryption
                17:d=2  hl=2 l=   0 prim:   NULL
                19:d=1  hl=4 l= 271 prim:  BIT STRING */
-            $tag = ord(self::_string_shift($key)); // skip over the BIT STRING / OCTET STRING tag
+            $tag = ord(Strings::shift($key)); // skip over the BIT STRING / OCTET STRING tag
             self::_decodeLength($key); // skip over the BIT STRING / OCTET STRING length
             // "The initial octet shall encode, as an unsigned binary integer wtih bit 1 as the least significant bit, the number of
             //  unused bits in the final subsequent octet. The number shall be in the range zero to seven."
             //  -- http://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf (section 8.6.2.2)
             if ($tag == self::ASN1_BITSTRING) {
-                self::_string_shift($key);
+                Strings::shift($key);
             }
-            if (ord(self::_string_shift($key)) != self::ASN1_SEQUENCE) {
+            if (ord(Strings::shift($key)) != self::ASN1_SEQUENCE) {
                 return false;
             }
             if (self::_decodeLength($key) != strlen($key)) {
                 return false;
             }
-            $tag = ord(self::_string_shift($key));
+            $tag = ord(Strings::shift($key));
         }
         if ($tag != self::ASN1_INTEGER) {
             return false;
         }
 
         $length = self::_decodeLength($key);
-        $temp = self::_string_shift($key, $length);
+        $temp = Strings::shift($key, $length);
         if (strlen($temp) != 1 || ord($temp) > 2) {
             $components['modulus'] = new BigInteger($temp, 256);
-            self::_string_shift($key); // skip over self::ASN1_INTEGER
+            Strings::shift($key); // skip over self::ASN1_INTEGER
             $length = self::_decodeLength($key);
-            $components[$components['isPublicKey'] ? 'publicExponent' : 'privateExponent'] = new BigInteger(self::_string_shift($key, $length), 256);
+            $components[$components['isPublicKey'] ? 'publicExponent' : 'privateExponent'] = new BigInteger(Strings::shift($key, $length), 256);
 
             return $components;
         }
-        if (ord(self::_string_shift($key)) != self::ASN1_INTEGER) {
+        if (ord(Strings::shift($key)) != self::ASN1_INTEGER) {
             return false;
         }
         $length = self::_decodeLength($key);
-        $components['modulus'] = new BigInteger(self::_string_shift($key, $length), 256);
-        self::_string_shift($key);
+        $components['modulus'] = new BigInteger(Strings::shift($key, $length), 256);
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['publicExponent'] = new BigInteger(self::_string_shift($key, $length), 256);
-        self::_string_shift($key);
+        $components['publicExponent'] = new BigInteger(Strings::shift($key, $length), 256);
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['privateExponent'] = new BigInteger(self::_string_shift($key, $length), 256);
-        self::_string_shift($key);
+        $components['privateExponent'] = new BigInteger(Strings::shift($key, $length), 256);
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['primes'] = array(1 => new BigInteger(self::_string_shift($key, $length), 256));
-        self::_string_shift($key);
+        $components['primes'] = array(1 => new BigInteger(Strings::shift($key, $length), 256));
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['primes'][] = new BigInteger(self::_string_shift($key, $length), 256);
-        self::_string_shift($key);
+        $components['primes'][] = new BigInteger(Strings::shift($key, $length), 256);
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['exponents'] = array(1 => new BigInteger(self::_string_shift($key, $length), 256));
-        self::_string_shift($key);
+        $components['exponents'] = array(1 => new BigInteger(Strings::shift($key, $length), 256));
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['exponents'][] = new BigInteger(self::_string_shift($key, $length), 256);
-        self::_string_shift($key);
+        $components['exponents'][] = new BigInteger(Strings::shift($key, $length), 256);
+        Strings::shift($key);
         $length = self::_decodeLength($key);
-        $components['coefficients'] = array(2 => new BigInteger(self::_string_shift($key, $length), 256));
+        $components['coefficients'] = array(2 => new BigInteger(Strings::shift($key, $length), 256));
 
         if (!empty($key)) {
-            if (ord(self::_string_shift($key)) != self::ASN1_SEQUENCE) {
+            if (ord(Strings::shift($key)) != self::ASN1_SEQUENCE) {
                 return false;
             }
             self::_decodeLength($key);
             while (!empty($key)) {
-                if (ord(self::_string_shift($key)) != self::ASN1_SEQUENCE) {
+                if (ord(Strings::shift($key)) != self::ASN1_SEQUENCE) {
                     return false;
                 }
                 self::_decodeLength($key);
                 $key = substr($key, 1);
                 $length = self::_decodeLength($key);
-                $components['primes'][] = new BigInteger(self::_string_shift($key, $length), 256);
-                self::_string_shift($key);
+                $components['primes'][] = new BigInteger(Strings::shift($key, $length), 256);
+                Strings::shift($key);
                 $length = self::_decodeLength($key);
-                $components['exponents'][] = new BigInteger(self::_string_shift($key, $length), 256);
-                self::_string_shift($key);
+                $components['exponents'][] = new BigInteger(Strings::shift($key, $length), 256);
+                Strings::shift($key);
                 $length = self::_decodeLength($key);
-                $components['coefficients'][] = new BigInteger(self::_string_shift($key, $length), 256);
+                $components['coefficients'][] = new BigInteger(Strings::shift($key, $length), 256);
             }
         }
 
@@ -412,10 +414,10 @@ abstract class PKCS
      */
     static function _decodeLength(&$string)
     {
-        $length = ord(self::_string_shift($string));
+        $length = ord(Strings::shift($string));
         if ($length & 0x80) { // definite length, long form
             $length&= 0x7F;
-            $temp = self::_string_shift($string, $length);
+            $temp = Strings::shift($string, $length);
             list(, $length) = unpack('N', substr(str_pad($temp, 4, chr(0), STR_PAD_LEFT), -4));
         }
         return $length;
@@ -441,23 +443,6 @@ abstract class PKCS
         return pack('Ca*', 0x80 | strlen($temp), $temp);
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    static function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * Extract raw BER from Base64 encoding
      *
diff --git a/phpseclib/Crypt/RSA/PuTTY.php b/phpseclib/Crypt/RSA/PuTTY.php
index 04c4ae20..14e8bd6f 100644
--- a/phpseclib/Crypt/RSA/PuTTY.php
+++ b/phpseclib/Crypt/RSA/PuTTY.php
@@ -19,6 +19,7 @@ use ParagonIE\ConstantTime\Hex;
 use phpseclib\Crypt\AES;
 use phpseclib\Crypt\Hash;
 use phpseclib\Math\BigInteger;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * PuTTY Formatted RSA Key Handler
@@ -117,10 +118,10 @@ class PuTTY
         $publicLength = trim(preg_replace('#Public-Lines: (\d+)#', '$1', $key[3]));
         $public = Base64::decode(implode('', array_map('trim', array_slice($key, 4, $publicLength))));
         $public = substr($public, 11);
-        extract(unpack('Nlength', self::_string_shift($public, 4)));
-        $components['publicExponent'] = new BigInteger(self::_string_shift($public, $length), -256);
-        extract(unpack('Nlength', self::_string_shift($public, 4)));
-        $components['modulus'] = new BigInteger(self::_string_shift($public, $length), -256);
+        extract(unpack('Nlength', Strings::shift($public, 4)));
+        $components['publicExponent'] = new BigInteger(Strings::shift($public, $length), -256);
+        extract(unpack('Nlength', Strings::shift($public, 4)));
+        $components['modulus'] = new BigInteger(Strings::shift($public, $length), -256);
 
         $privateLength = trim(preg_replace('#Private-Lines: (\d+)#', '$1', $key[$publicLength + 4]));
         $private = Base64::decode(implode('', array_map('trim', array_slice($key, $publicLength + 5, $privateLength))));
@@ -141,53 +142,36 @@ class PuTTY
             }
         }
 
-        extract(unpack('Nlength', self::_string_shift($private, 4)));
+        extract(unpack('Nlength', Strings::shift($private, 4)));
         if (strlen($private) < $length) {
             return false;
         }
-        $components['privateExponent'] = new BigInteger(self::_string_shift($private, $length), -256);
-        extract(unpack('Nlength', self::_string_shift($private, 4)));
+        $components['privateExponent'] = new BigInteger(Strings::shift($private, $length), -256);
+        extract(unpack('Nlength', Strings::shift($private, 4)));
         if (strlen($private) < $length) {
             return false;
         }
-        $components['primes'] = array(1 => new BigInteger(self::_string_shift($private, $length), -256));
-        extract(unpack('Nlength', self::_string_shift($private, 4)));
+        $components['primes'] = array(1 => new BigInteger(Strings::shift($private, $length), -256));
+        extract(unpack('Nlength', Strings::shift($private, 4)));
         if (strlen($private) < $length) {
             return false;
         }
-        $components['primes'][] = new BigInteger(self::_string_shift($private, $length), -256);
+        $components['primes'][] = new BigInteger(Strings::shift($private, $length), -256);
 
         $temp = $components['primes'][1]->subtract($one);
         $components['exponents'] = array(1 => $components['publicExponent']->modInverse($temp));
         $temp = $components['primes'][2]->subtract($one);
         $components['exponents'][] = $components['publicExponent']->modInverse($temp);
 
-        extract(unpack('Nlength', self::_string_shift($private, 4)));
+        extract(unpack('Nlength', Strings::shift($private, 4)));
         if (strlen($private) < $length) {
             return false;
         }
-        $components['coefficients'] = array(2 => new BigInteger(self::_string_shift($private, $length), -256));
+        $components['coefficients'] = array(2 => new BigInteger(Strings::shift($private, $length), -256));
 
         return $components;
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    static function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * Convert a private key to the appropriate format.
      *
diff --git a/phpseclib/Crypt/Random.php b/phpseclib/Crypt/Random.php
index 6bf61468..c102e5e0 100644
--- a/phpseclib/Crypt/Random.php
+++ b/phpseclib/Crypt/Random.php
@@ -24,6 +24,8 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\BlockCipher;
+
 /**
  * Pure-PHP Random Number Generator
  *
@@ -139,19 +141,19 @@ class Random
             // http://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator#Designs_based_on_cryptographic_primitives
             switch (true) {
                 case class_exists('\phpseclib\Crypt\AES'):
-                    $crypto = new AES(Base::MODE_CTR);
+                    $crypto = new AES(BlockCipher::MODE_CTR);
                     break;
                 case class_exists('\phpseclib\Crypt\Twofish'):
-                    $crypto = new Twofish(Base::MODE_CTR);
+                    $crypto = new Twofish(BlockCipher::MODE_CTR);
                     break;
                 case class_exists('\phpseclib\Crypt\Blowfish'):
-                    $crypto = new Blowfish(Base::MODE_CTR);
+                    $crypto = new Blowfish(BlockCipher::MODE_CTR);
                     break;
                 case class_exists('\phpseclib\Crypt\TripleDES'):
-                    $crypto = new TripleDES(Base::MODE_CTR);
+                    $crypto = new TripleDES(BlockCipher::MODE_CTR);
                     break;
                 case class_exists('\phpseclib\Crypt\DES'):
-                    $crypto = new DES(Base::MODE_CTR);
+                    $crypto = new DES(BlockCipher::MODE_CTR);
                     break;
                 case class_exists('\phpseclib\Crypt\RC4'):
                     $crypto = new RC4();
diff --git a/phpseclib/Crypt/Rijndael.php b/phpseclib/Crypt/Rijndael.php
index c98f02e2..a5010a80 100644
--- a/phpseclib/Crypt/Rijndael.php
+++ b/phpseclib/Crypt/Rijndael.php
@@ -54,6 +54,8 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\BlockCipher;
+
 /**
  * Pure-PHP implementation of Rijndael.
  *
@@ -61,7 +63,7 @@ namespace phpseclib\Crypt;
  * @author  Jim Wigginton <terrafrost@php.net>
  * @access  public
  */
-class Rijndael extends Base
+class Rijndael extends BlockCipher
 {
     /**
      * The mcrypt specific name of the cipher
@@ -71,8 +73,8 @@ class Rijndael extends Base
      * or not for the current $block_size/$key_length.
      * In case of, $cipher_name_mcrypt will be set dynamically at run time accordingly.
      *
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
-     * @see \phpseclib\Crypt\Base::engine
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::engine
      * @see self::isValidEngine()
      * @var string
      * @access private
@@ -82,8 +84,8 @@ class Rijndael extends Base
     /**
      * The default salt used by setPassword()
      *
-     * @see \phpseclib\Crypt\Base::password_default_salt
-     * @see \phpseclib\Crypt\Base::setPassword()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::password_default_salt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setPassword()
      * @var string
      * @access private
      */
@@ -277,9 +279,9 @@ class Rijndael extends Base
     /**
      * Test for engine validity
      *
-     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Base::isValidEngine()
+     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      *
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      * @param int $engine
      * @access public
      * @return bool
@@ -499,7 +501,7 @@ class Rijndael extends Base
     /**
      * Setup the key (expansion)
      *
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
@@ -804,7 +806,7 @@ class Rijndael extends Base
     /**
      * Setup the performance-optimized function for de/encrypt()
      *
-     * @see \phpseclib\Crypt\Base::_setupInlineCrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupInlineCrypt()
      * @access private
      */
     function _setupInlineCrypt()
diff --git a/phpseclib/Crypt/TripleDES.php b/phpseclib/Crypt/TripleDES.php
index 29c6eb9d..11cf976d 100644
--- a/phpseclib/Crypt/TripleDES.php
+++ b/phpseclib/Crypt/TripleDES.php
@@ -55,9 +55,9 @@ class TripleDES extends DES
     /**
      * Encrypt / decrypt using outer chaining
      *
-     * Outer chaining is used by SSH-2 and when the mode is set to \phpseclib\Crypt\Base::MODE_CBC.
+     * Outer chaining is used by SSH-2 and when the mode is set to \phpseclib\Crypt\Common\BlockCipher::MODE_CBC.
      */
-    const MODE_CBC3 = Base::MODE_CBC;
+    const MODE_CBC3 = self::MODE_CBC;
 
     /**
      * Key Length (in bytes)
@@ -71,8 +71,8 @@ class TripleDES extends DES
     /**
      * The default salt used by setPassword()
      *
-     * @see \phpseclib\Crypt\Base::password_default_salt
-     * @see \phpseclib\Crypt\Base::setPassword()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::password_default_salt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setPassword()
      * @var string
      * @access private
      */
@@ -82,7 +82,7 @@ class TripleDES extends DES
      * The mcrypt specific name of the cipher
      *
      * @see \phpseclib\Crypt\DES::cipher_name_mcrypt
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
      * @var string
      * @access private
      */
@@ -91,7 +91,7 @@ class TripleDES extends DES
     /**
      * Optimizing value while CFB-encrypting
      *
-     * @see \phpseclib\Crypt\Base::cfb_init_len
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cfb_init_len
      * @var int
      * @access private
      */
@@ -132,20 +132,20 @@ class TripleDES extends DES
      *
      * $mode could be:
      *
-     * - \phpseclib\Crypt\Base::MODE_ECB
+     * - \phpseclib\Crypt\Common\BlockCipher::MODE_ECB
      *
-     * - \phpseclib\Crypt\Base::MODE_CBC
+     * - \phpseclib\Crypt\Common\BlockCipher::MODE_CBC
      *
-     * - \phpseclib\Crypt\Base::MODE_CTR
+     * - \phpseclib\Crypt\Common\BlockCipher::MODE_CTR
      *
-     * - \phpseclib\Crypt\Base::MODE_CFB
+     * - \phpseclib\Crypt\Common\BlockCipher::MODE_CFB
      *
-     * - \phpseclib\Crypt\Base::MODE_OFB
+     * - \phpseclib\Crypt\Common\BlockCipher::MODE_OFB
      *
      * - \phpseclib\Crypt\TripleDES::MODE_3CB
      *
      * @see \phpseclib\Crypt\DES::__construct()
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      * @param int $mode
      * @access public
      */
@@ -155,14 +155,14 @@ class TripleDES extends DES
             // In case of self::MODE_3CBC, we init as CRYPT_DES_MODE_CBC
             // and additional flag us internally as 3CBC
             case self::MODE_3CBC:
-                parent::__construct(Base::MODE_CBC);
+                parent::__construct(self::MODE_CBC);
                 $this->mode_3cbc = true;
 
                 // This three $des'es will do the 3CBC work (if $key > 64bits)
                 $this->des = array(
-                    new DES(Base::MODE_CBC),
-                    new DES(Base::MODE_CBC),
-                    new DES(Base::MODE_CBC),
+                    new DES(self::MODE_CBC),
+                    new DES(self::MODE_CBC),
+                    new DES(self::MODE_CBC),
                 );
 
                 // we're going to be doing the padding, ourselves, so disable it in the \phpseclib\Crypt\DES objects
@@ -179,9 +179,9 @@ class TripleDES extends DES
     /**
      * Test for engine validity
      *
-     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Base::isValidEngine()
+     * This is mainly just a wrapper to set things up for \phpseclib\Crypt\Common\SymmetricKey::isValidEngine()
      *
-     * @see \phpseclib\Crypt\Base::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
      * @param int $engine
      * @access public
      * @return bool
@@ -200,9 +200,9 @@ class TripleDES extends DES
     /**
      * Sets the initialization vector.
      *
-     * SetIV is not required when \phpseclib\Crypt\Base::MODE_ECB is being used.
+     * SetIV is not required when \phpseclib\Crypt\Common\SymmetricKey::MODE_ECB is being used.
      *
-     * @see \phpseclib\Crypt\Base::setIV()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setIV()
      * @access public
      * @param string $iv
      */
@@ -223,7 +223,7 @@ class TripleDES extends DES
      *
      * If you want to use a 64-bit key use DES.php
      *
-     * @see \phpseclib\Crypt\Base:setKeyLength()
+     * @see \phpseclib\Crypt\Common\SymmetricKey:setKeyLength()
      * @access public
      * @throws \LengthException if the key length is invalid
      * @param int $length
@@ -250,7 +250,7 @@ class TripleDES extends DES
      *
      * @access public
      * @see \phpseclib\Crypt\DES::setKey()
-     * @see \phpseclib\Crypt\Base::setKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setKey()
      * @throws \LengthException if the key length is invalid
      * @param string $key
      */
@@ -269,7 +269,7 @@ class TripleDES extends DES
                 throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16 or 24 are supported');
         }
 
-        // copied from Base::setKey()
+        // copied from self::setKey()
         $this->key = $key;
         $this->key_length = strlen($key);
         $this->changed = true;
@@ -285,7 +285,7 @@ class TripleDES extends DES
     /**
      * Encrypts a message.
      *
-     * @see \phpseclib\Crypt\Base::encrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::encrypt()
      * @access public
      * @param string $plaintext
      * @return string $cipertext
@@ -312,7 +312,7 @@ class TripleDES extends DES
     /**
      * Decrypts a message.
      *
-     * @see \phpseclib\Crypt\Base::decrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::decrypt()
      * @access public
      * @param string $ciphertext
      * @return string $plaintext
@@ -368,7 +368,7 @@ class TripleDES extends DES
      * continuous buffers not be used.  They do offer better security and are, in fact, sometimes required (SSH uses them),
      * however, they are also less intuitive and more likely to cause you problems.
      *
-     * @see \phpseclib\Crypt\Base::enableContinuousBuffer()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::enableContinuousBuffer()
      * @see self::disableContinuousBuffer()
      * @access public
      */
@@ -387,7 +387,7 @@ class TripleDES extends DES
      *
      * The default behavior.
      *
-     * @see \phpseclib\Crypt\Base::disableContinuousBuffer()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::disableContinuousBuffer()
      * @see self::enableContinuousBuffer()
      * @access public
      */
@@ -405,7 +405,7 @@ class TripleDES extends DES
      * Creates the key schedule
      *
      * @see \phpseclib\Crypt\DES::_setupKey()
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
@@ -439,8 +439,8 @@ class TripleDES extends DES
     /**
      * Sets the internal crypt engine
      *
-     * @see \phpseclib\Crypt\Base::__construct()
-     * @see \phpseclib\Crypt\Base::setPreferredEngine()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::__construct()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::setPreferredEngine()
      * @param int $engine
      * @access public
      * @return int
diff --git a/phpseclib/Crypt/Twofish.php b/phpseclib/Crypt/Twofish.php
index e4d910db..e72f91f7 100644
--- a/phpseclib/Crypt/Twofish.php
+++ b/phpseclib/Crypt/Twofish.php
@@ -37,6 +37,8 @@
 
 namespace phpseclib\Crypt;
 
+use phpseclib\Crypt\Common\BlockCipher;
+
 /**
  * Pure-PHP implementation of Twofish.
  *
@@ -45,12 +47,12 @@ namespace phpseclib\Crypt;
  * @author  Hans-Juergen Petrich <petrich@tronic-media.com>
  * @access  public
  */
-class Twofish extends Base
+class Twofish extends BlockCipher
 {
     /**
      * The mcrypt specific name of the cipher
      *
-     * @see \phpseclib\Crypt\Base::cipher_name_mcrypt
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cipher_name_mcrypt
      * @var string
      * @access private
      */
@@ -59,7 +61,7 @@ class Twofish extends Base
     /**
      * Optimizing value while CFB-encrypting
      *
-     * @see \phpseclib\Crypt\Base::cfb_init_len
+     * @see \phpseclib\Crypt\Common\SymmetricKey::cfb_init_len
      * @var int
      * @access private
      */
@@ -433,7 +435,7 @@ class Twofish extends Base
     /**
      * Setup the key (expansion)
      *
-     * @see \phpseclib\Crypt\Base::_setupKey()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupKey()
      * @access private
      */
     function _setupKey()
@@ -700,7 +702,7 @@ class Twofish extends Base
     /**
      * Setup the performance-optimized function for de/encrypt()
      *
-     * @see \phpseclib\Crypt\Base::_setupInlineCrypt()
+     * @see \phpseclib\Crypt\Common\SymmetricKey::_setupInlineCrypt()
      * @access private
      */
     function _setupInlineCrypt()
diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
index 34430c3e..42f0e882 100644
--- a/phpseclib/File/ASN1.php
+++ b/phpseclib/File/ASN1.php
@@ -1207,23 +1207,6 @@ class ASN1
         $this->filters = $filters;
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * String type conversion
      *
diff --git a/phpseclib/Net/SCP.php b/phpseclib/Net/SCP.php
index 4c28d8b0..288f8231 100644
--- a/phpseclib/Net/SCP.php
+++ b/phpseclib/Net/SCP.php
@@ -33,6 +33,7 @@
 namespace phpseclib\Net;
 
 use phpseclib\Exception\FileNotFoundException;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Pure-PHP implementations of SCP.
@@ -305,7 +306,7 @@ class SCP
                     switch ($response[SSH1::RESPONSE_TYPE]) {
                         case NET_SSH1_SMSG_STDOUT_DATA:
                             extract(unpack('Nlength', $response[SSH1::RESPONSE_DATA]));
-                            return $this->ssh->_string_shift($response[SSH1::RESPONSE_DATA], $length);
+                            return Strings::shift($response[SSH1::RESPONSE_DATA], $length);
                         case NET_SSH1_SMSG_STDERR_DATA:
                             break;
                         case NET_SSH1_SMSG_EXITSTATUS:
diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index 0f8bb58e..7f01b119 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -39,6 +39,7 @@ namespace phpseclib\Net;
 
 use ParagonIE\ConstantTime\Hex;
 use phpseclib\Exception\FileNotFoundException;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Pure-PHP implementations of SFTP.
@@ -475,13 +476,13 @@ class SFTP extends SSH2
             throw new \UnexpectedValueException('Expected SSH_FXP_VERSION');
         }
 
-        extract(unpack('Nversion', $this->_string_shift($response, 4)));
+        extract(unpack('Nversion', Strings::shift($response, 4)));
         $this->version = $version;
         while (!empty($response)) {
-            extract(unpack('Nlength', $this->_string_shift($response, 4)));
-            $key = $this->_string_shift($response, $length);
-            extract(unpack('Nlength', $this->_string_shift($response, 4)));
-            $value = $this->_string_shift($response, $length);
+            extract(unpack('Nlength', Strings::shift($response, 4)));
+            $key = Strings::shift($response, $length);
+            extract(unpack('Nlength', Strings::shift($response, 4)));
+            $value = Strings::shift($response, $length);
             $this->extensions[$key] = $value;
         }
 
@@ -590,14 +591,14 @@ class SFTP extends SSH2
     function _logError($response, $status = -1)
     {
         if ($status == -1) {
-            extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+            extract(unpack('Nstatus', Strings::shift($response, 4)));
         }
 
         $error = $this->status_codes[$status];
 
         if ($this->version > 2) {
-            extract(unpack('Nlength', $this->_string_shift($response, 4)));
-            $this->sftp_errors[] = $error . ': ' . $this->_string_shift($response, $length);
+            extract(unpack('Nlength', Strings::shift($response, 4)));
+            $this->sftp_errors[] = $error . ': ' . Strings::shift($response, $length);
         } else {
             $this->sftp_errors[] = $error;
         }
@@ -644,9 +645,9 @@ class SFTP extends SSH2
                     // although SSH_FXP_NAME is implemented differently in SFTPv3 than it is in SFTPv4+, the following
                     // should work on all SFTP versions since the only part of the SSH_FXP_NAME packet the following looks
                     // at is the first part and that part is defined the same in SFTP versions 3 through 6.
-                    $this->_string_shift($response, 4); // skip over the count - it should be 1, anyway
-                    extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                    return $this->_string_shift($response, $length);
+                    Strings::shift($response, 4); // skip over the count - it should be 1, anyway
+                    extract(unpack('Nlength', Strings::shift($response, 4)));
+                    return Strings::shift($response, $length);
                 case NET_SFTP_STATUS:
                     $this->_logError($response);
                     return false;
@@ -878,12 +879,12 @@ class SFTP extends SSH2
             $response = $this->_get_sftp_packet();
             switch ($this->packet_type) {
                 case NET_SFTP_NAME:
-                    extract(unpack('Ncount', $this->_string_shift($response, 4)));
+                    extract(unpack('Ncount', Strings::shift($response, 4)));
                     for ($i = 0; $i < $count; $i++) {
-                        extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                        $shortname = $this->_string_shift($response, $length);
-                        extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                        $longname = $this->_string_shift($response, $length);
+                        extract(unpack('Nlength', Strings::shift($response, 4)));
+                        $shortname = Strings::shift($response, $length);
+                        extract(unpack('Nlength', Strings::shift($response, 4)));
+                        $longname = Strings::shift($response, $length);
                         $attributes = $this->_parseAttributes($response);
                         if (!isset($attributes['type'])) {
                             $fileType = $this->_parseLongname($longname);
@@ -908,7 +909,7 @@ class SFTP extends SSH2
                     }
                     break;
                 case NET_SFTP_STATUS:
-                    extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+                    extract(unpack('Nstatus', Strings::shift($response, 4)));
                     if ($status != NET_SFTP_STATUS_EOF) {
                         $this->_logError($response, $status);
                         return false;
@@ -1501,7 +1502,7 @@ class SFTP extends SSH2
             throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             $this->_logError($response, $status);
             return false;
@@ -1613,14 +1614,14 @@ class SFTP extends SSH2
                 throw new \UnexpectedValueException('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
         }
 
-        extract(unpack('Ncount', $this->_string_shift($response, 4)));
+        extract(unpack('Ncount', Strings::shift($response, 4)));
         // the file isn't a symlink
         if (!$count) {
             return false;
         }
 
-        extract(unpack('Nlength', $this->_string_shift($response, 4)));
-        return $this->_string_shift($response, $length);
+        extract(unpack('Nlength', Strings::shift($response, 4)));
+        return Strings::shift($response, $length);
     }
 
     /**
@@ -1653,7 +1654,7 @@ class SFTP extends SSH2
             throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             $this->_logError($response, $status);
             return false;
@@ -1716,7 +1717,7 @@ class SFTP extends SSH2
             throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             $this->_logError($response, $status);
             return false;
@@ -1753,7 +1754,7 @@ class SFTP extends SSH2
             throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             // presumably SSH_FX_NO_SUCH_FILE or SSH_FX_PERMISSION_DENIED?
             $this->_logError($response, $status);
@@ -1979,7 +1980,7 @@ class SFTP extends SSH2
                 throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
             }
 
-            extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+            extract(unpack('Nstatus', Strings::shift($response, 4)));
             if ($status != NET_SFTP_STATUS_OK) {
                 $this->_logError($response, $status);
                 break;
@@ -2010,7 +2011,7 @@ class SFTP extends SSH2
             throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             $this->_logError($response, $status);
             return false;
@@ -2200,7 +2201,7 @@ class SFTP extends SSH2
         }
 
         // if $status isn't SSH_FX_OK it's probably SSH_FX_NO_SUCH_FILE or SSH_FX_PERMISSION_DENIED
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             $this->_logError($response, $status);
             if (!$recursive) {
@@ -2625,7 +2626,7 @@ class SFTP extends SSH2
         }
 
         // if $status isn't SSH_FX_OK it's probably SSH_FX_NO_SUCH_FILE or SSH_FX_PERMISSION_DENIED
-        extract(unpack('Nstatus', $this->_string_shift($response, 4)));
+        extract(unpack('Nstatus', Strings::shift($response, 4)));
         if ($status != NET_SFTP_STATUS_OK) {
             $this->_logError($response, $status);
             return false;
@@ -2652,7 +2653,7 @@ class SFTP extends SSH2
     function _parseAttributes(&$response)
     {
         $attr = array();
-        extract(unpack('Nflags', $this->_string_shift($response, 4)));
+        extract(unpack('Nflags', Strings::shift($response, 4)));
         // SFTPv4+ have a type field (a byte) that follows the above flag field
         foreach ($this->attributes as $key => $value) {
             switch ($flags & $key) {
@@ -2663,13 +2664,13 @@ class SFTP extends SSH2
                     // IEEE 754 binary64 "double precision" on such platforms and
                     // as such can represent integers of at least 2^50 without loss
                     // of precision. Interpreted in filesize, 2^50 bytes = 1024 TiB.
-                    $attr['size'] = hexdec(Hex::encode($this->_string_shift($response, 8)));
+                    $attr['size'] = hexdec(Hex::encode(Strings::shift($response, 8)));
                     break;
                 case NET_SFTP_ATTR_UIDGID: // 0x00000002 (SFTPv3 only)
-                    $attr+= unpack('Nuid/Ngid', $this->_string_shift($response, 8));
+                    $attr+= unpack('Nuid/Ngid', Strings::shift($response, 8));
                     break;
                 case NET_SFTP_ATTR_PERMISSIONS: // 0x00000004
-                    $attr+= unpack('Npermissions', $this->_string_shift($response, 4));
+                    $attr+= unpack('Npermissions', Strings::shift($response, 4));
                     // mode == permissions; permissions was the original array key and is retained for bc purposes.
                     // mode was added because that's the more industry standard terminology
                     $attr+= array('mode' => $attr['permissions']);
@@ -2679,15 +2680,15 @@ class SFTP extends SSH2
                     }
                     break;
                 case NET_SFTP_ATTR_ACCESSTIME: // 0x00000008
-                    $attr+= unpack('Natime/Nmtime', $this->_string_shift($response, 8));
+                    $attr+= unpack('Natime/Nmtime', Strings::shift($response, 8));
                     break;
                 case NET_SFTP_ATTR_EXTENDED: // 0x80000000
-                    extract(unpack('Ncount', $this->_string_shift($response, 4)));
+                    extract(unpack('Ncount', Strings::shift($response, 4)));
                     for ($i = 0; $i < $count; $i++) {
-                        extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                        $key = $this->_string_shift($response, $length);
-                        extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                        $attr[$key] = $this->_string_shift($response, $length);
+                        extract(unpack('Nlength', Strings::shift($response, 4)));
+                        $key = Strings::shift($response, $length);
+                        extract(unpack('Nlength', Strings::shift($response, 4)));
+                        $attr[$key] = Strings::shift($response, $length);
                     }
             }
         }
@@ -2839,7 +2840,7 @@ class SFTP extends SSH2
             }
             $this->packet_buffer.= $temp;
         }
-        extract(unpack('Nlength', $this->_string_shift($this->packet_buffer, 4)));
+        extract(unpack('Nlength', Strings::shift($this->packet_buffer, 4)));
         $tempLength = $length;
         $tempLength-= strlen($this->packet_buffer);
 
@@ -2857,16 +2858,16 @@ class SFTP extends SSH2
 
         $stop = strtok(microtime(), ' ') + strtok('');
 
-        $this->packet_type = ord($this->_string_shift($this->packet_buffer));
+        $this->packet_type = ord(Strings::shift($this->packet_buffer));
 
         if ($this->request_id !== false) {
-            $this->_string_shift($this->packet_buffer, 4); // remove the request id
+            Strings::shift($this->packet_buffer, 4); // remove the request id
             $length-= 5; // account for the request id and the packet type
         } else {
             $length-= 1; // account for the packet type
         }
 
-        $packet = $this->_string_shift($this->packet_buffer, $length);
+        $packet = Strings::shift($this->packet_buffer, $length);
 
         if (defined('NET_SFTP_LOGGING')) {
             $packet_type = '<- ' . $this->packet_types[$this->packet_type] .
diff --git a/phpseclib/Net/SSH1.php b/phpseclib/Net/SSH1.php
index 2ed4a002..ea42d052 100644
--- a/phpseclib/Net/SSH1.php
+++ b/phpseclib/Net/SSH1.php
@@ -53,6 +53,7 @@ use phpseclib\Crypt\DES;
 use phpseclib\Crypt\Random;
 use phpseclib\Crypt\TripleDES;
 use phpseclib\Math\BigInteger;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Pure-PHP implementation of SSHv1.
@@ -570,32 +571,32 @@ class SSH1
             throw new \UnexpectedValueException('Expected SSH_SMSG_PUBLIC_KEY');
         }
 
-        $anti_spoofing_cookie = $this->_string_shift($response[self::RESPONSE_DATA], 8);
+        $anti_spoofing_cookie = Strings::shift($response[self::RESPONSE_DATA], 8);
 
-        $this->_string_shift($response[self::RESPONSE_DATA], 4);
+        Strings::shift($response[self::RESPONSE_DATA], 4);
 
-        $temp = unpack('nlen', $this->_string_shift($response[self::RESPONSE_DATA], 2));
-        $server_key_public_exponent = new BigInteger($this->_string_shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
+        $temp = unpack('nlen', Strings::shift($response[self::RESPONSE_DATA], 2));
+        $server_key_public_exponent = new BigInteger(Strings::shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
         $this->server_key_public_exponent = $server_key_public_exponent;
 
-        $temp = unpack('nlen', $this->_string_shift($response[self::RESPONSE_DATA], 2));
-        $server_key_public_modulus = new BigInteger($this->_string_shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
+        $temp = unpack('nlen', Strings::shift($response[self::RESPONSE_DATA], 2));
+        $server_key_public_modulus = new BigInteger(Strings::shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
         $this->server_key_public_modulus = $server_key_public_modulus;
 
-        $this->_string_shift($response[self::RESPONSE_DATA], 4);
+        Strings::shift($response[self::RESPONSE_DATA], 4);
 
-        $temp = unpack('nlen', $this->_string_shift($response[self::RESPONSE_DATA], 2));
-        $host_key_public_exponent = new BigInteger($this->_string_shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
+        $temp = unpack('nlen', Strings::shift($response[self::RESPONSE_DATA], 2));
+        $host_key_public_exponent = new BigInteger(Strings::shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
         $this->host_key_public_exponent = $host_key_public_exponent;
 
-        $temp = unpack('nlen', $this->_string_shift($response[self::RESPONSE_DATA], 2));
-        $host_key_public_modulus = new BigInteger($this->_string_shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
+        $temp = unpack('nlen', Strings::shift($response[self::RESPONSE_DATA], 2));
+        $host_key_public_modulus = new BigInteger(Strings::shift($response[self::RESPONSE_DATA], ceil($temp['len'] / 8)), 256);
         $this->host_key_public_modulus = $host_key_public_modulus;
 
-        $this->_string_shift($response[self::RESPONSE_DATA], 4);
+        Strings::shift($response[self::RESPONSE_DATA], 4);
 
         // get a list of the supported ciphers
-        extract(unpack('Nsupported_ciphers_mask', $this->_string_shift($response[self::RESPONSE_DATA], 4)));
+        extract(unpack('Nsupported_ciphers_mask', Strings::shift($response[self::RESPONSE_DATA], 4)));
         foreach ($this->supported_ciphers as $mask => $name) {
             if (($supported_ciphers_mask & (1 << $mask)) == 0) {
                 unset($this->supported_ciphers[$mask]);
@@ -603,7 +604,7 @@ class SSH1
         }
 
         // get a list of the supported authentications
-        extract(unpack('Nsupported_authentications_mask', $this->_string_shift($response[self::RESPONSE_DATA], 4)));
+        extract(unpack('Nsupported_authentications_mask', Strings::shift($response[self::RESPONSE_DATA], 4)));
         foreach ($this->supported_authentications as $mask => $name) {
             if (($supported_authentications_mask & (1 << $mask)) == 0) {
                 unset($this->supported_authentications[$mask]);
@@ -920,12 +921,12 @@ class SSH1
             }
             $pos = strlen($match) ? strpos($this->interactiveBuffer, $match) : false;
             if ($pos !== false) {
-                return $this->_string_shift($this->interactiveBuffer, $pos + strlen($match));
+                return Strings::shift($this->interactiveBuffer, $pos + strlen($match));
             }
             $response = $this->_get_binary_packet();
 
             if ($response === true) {
-                return $this->_string_shift($this->interactiveBuffer, strlen($this->interactiveBuffer));
+                return Strings::shift($this->interactiveBuffer, strlen($this->interactiveBuffer));
             }
             $this->interactiveBuffer.= substr($response[self::RESPONSE_DATA], 4);
         }
@@ -1272,23 +1273,6 @@ class SSH1
         return $crc;
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * RSA Encrypt
      *
@@ -1409,7 +1393,7 @@ class SSH1
                 if (strlen($current_log)) {
                     $output.= str_pad(dechex($j), 7, '0', STR_PAD_LEFT) . '0  ';
                 }
-                $fragment = $this->_string_shift($current_log, $this->log_short_width);
+                $fragment = Strings::shift($current_log, $this->log_short_width);
                 $hex = substr(preg_replace_callback('#.#s', array($this, '_format_log_helper'), $fragment), strlen($this->log_boundary));
                 // replace non ASCII printable characters with dots
                 // http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
@@ -1559,7 +1543,7 @@ class SSH1
             // the most useful log for SSH1
             case self::LOG_COMPLEX:
                 $this->protocol_flags_log[] = $protocol_flags;
-                $this->_string_shift($message);
+                Strings::shift($message);
                 $this->log_size+= strlen($message);
                 $this->message_log[] = $message;
                 while ($this->log_size > self::LOG_MAX_SIZE) {
diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index b8993075..e9e9ac46 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -50,7 +50,7 @@
 namespace phpseclib\Net;
 
 use ParagonIE\ConstantTime\Base64;
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\Blowfish;
 use phpseclib\Crypt\Hash;
 use phpseclib\Crypt\Random;
@@ -62,6 +62,7 @@ use phpseclib\Crypt\Twofish;
 use phpseclib\Math\BigInteger; // Used to do Diffie-Hellman key exchange and DSA/RSA signature verification.
 use phpseclib\System\SSH\Agent;
 use phpseclib\Exception\NoSupportedAlgorithmsException;
+use phpseclib\Common\Functions\Strings;
 
 /**
  * Pure-PHP implementation of SSHv2.
@@ -1303,40 +1304,40 @@ class SSH2
         $client_cookie = Random::string(16);
 
         $response = $kexinit_payload_server;
-        $this->_string_shift($response, 1); // skip past the message number (it should be SSH_MSG_KEXINIT)
-        $server_cookie = $this->_string_shift($response, 16);
+        Strings::shift($response, 1); // skip past the message number (it should be SSH_MSG_KEXINIT)
+        $server_cookie = Strings::shift($response, 16);
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->kex_algorithms = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->kex_algorithms = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->server_host_key_algorithms = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->server_host_key_algorithms = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->encryption_algorithms_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->encryption_algorithms_client_to_server = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->encryption_algorithms_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->encryption_algorithms_server_to_client = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->mac_algorithms_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->mac_algorithms_client_to_server = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->mac_algorithms_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->mac_algorithms_server_to_client = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->compression_algorithms_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->compression_algorithms_client_to_server = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->compression_algorithms_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->compression_algorithms_server_to_client = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->languages_client_to_server = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->languages_client_to_server = explode(',', Strings::shift($response, $temp['length']));
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->languages_server_to_client = explode(',', $this->_string_shift($response, $temp['length']));
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->languages_server_to_client = explode(',', Strings::shift($response, $temp['length']));
 
-        extract(unpack('Cfirst_kex_packet_follows', $this->_string_shift($response, 1)));
+        extract(unpack('Cfirst_kex_packet_follows', Strings::shift($response, 1)));
         $first_kex_packet_follows = $first_kex_packet_follows != 0;
 
         // the sending of SSH2_MSG_KEXINIT could go in one of two places.  this is the second place.
@@ -1429,18 +1430,18 @@ class SSH2
                     user_error('Connection closed by server');
                     return false;
                 }
-                extract(unpack('Ctype', $this->_string_shift($response, 1)));
+                extract(unpack('Ctype', Strings::shift($response, 1)));
                 if ($type != NET_SSH2_MSG_KEXDH_GEX_GROUP) {
                     user_error('Expected SSH_MSG_KEX_DH_GEX_GROUP');
                     return false;
                 }
 
-                extract(unpack('NprimeLength', $this->_string_shift($response, 4)));
-                $primeBytes = $this->_string_shift($response, $primeLength);
+                extract(unpack('NprimeLength', Strings::shift($response, 4)));
+                $primeBytes = Strings::shift($response, $primeLength);
                 $prime = new BigInteger($primeBytes, -256);
 
-                extract(unpack('NgLength', $this->_string_shift($response, 4)));
-                $gBytes = $this->_string_shift($response, $gLength);
+                extract(unpack('NgLength', Strings::shift($response, 4)));
+                $gBytes = Strings::shift($response, $gLength);
                 $g = new BigInteger($gBytes, -256);
 
                 $exchange_hash_rfc4419 = pack(
@@ -1519,26 +1520,26 @@ class SSH2
         if ($response === false) {
             throw new \RuntimeException('Connection closed by server');
         }
-        extract(unpack('Ctype', $this->_string_shift($response, 1)));
+        extract(unpack('Ctype', Strings::shift($response, 1)));
 
         if ($type != $serverKexReplyMessage) {
             throw new \UnexpectedValueException('Expected SSH_MSG_KEXDH_REPLY');
         }
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->server_public_host_key = $server_public_host_key = $this->_string_shift($response, $temp['length']);
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->server_public_host_key = $server_public_host_key = Strings::shift($response, $temp['length']);
 
-        $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-        $public_key_format = $this->_string_shift($server_public_host_key, $temp['length']);
+        $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+        $public_key_format = Strings::shift($server_public_host_key, $temp['length']);
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $fBytes = $this->_string_shift($response, $temp['length']);
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $fBytes = Strings::shift($response, $temp['length']);
 
-        $temp = unpack('Nlength', $this->_string_shift($response, 4));
-        $this->signature = $this->_string_shift($response, $temp['length']);
+        $temp = unpack('Nlength', Strings::shift($response, 4));
+        $this->signature = Strings::shift($response, $temp['length']);
 
-        $temp = unpack('Nlength', $this->_string_shift($this->signature, 4));
-        $this->signature_format = $this->_string_shift($this->signature, $temp['length']);
+        $temp = unpack('Nlength', Strings::shift($this->signature, 4));
+        $this->signature_format = Strings::shift($this->signature, $temp['length']);
 
         if ($kex_algorithm === 'curve25519-sha256@libssh.org') {
             if (strlen($fBytes) !== 32) {
@@ -1606,7 +1607,7 @@ class SSH2
             throw new \RuntimeException('Connection closed by server');
         }
 
-        extract(unpack('Ctype', $this->_string_shift($response, 1)));
+        extract(unpack('Ctype', Strings::shift($response, 1)));
 
         if ($type != NET_SSH2_MSG_NEWKEYS) {
             throw new \UnexpectedValueException('Expected SSH_MSG_NEWKEYS');
@@ -1824,30 +1825,30 @@ class SSH2
     {
         switch ($algorithm) {
             case '3des-cbc':
-                return new TripleDES(Base::MODE_CBC);
+                return new TripleDES(BlockCipher::MODE_CBC);
             case '3des-ctr':
-                return new TripleDES(Base::MODE_CTR);
+                return new TripleDES(BlockCipher::MODE_CTR);
             case 'aes256-cbc':
             case 'aes192-cbc':
             case 'aes128-cbc':
-                return new Rijndael(Base::MODE_CBC);
+                return new Rijndael(BlockCipher::MODE_CBC);
             case 'aes256-ctr':
             case 'aes192-ctr':
             case 'aes128-ctr':
-                return new Rijndael(Base::MODE_CTR);
+                return new Rijndael(BlockCipher::MODE_CTR);
             case 'blowfish-cbc':
-                return new Blowfish(Base::MODE_CBC);
+                return new Blowfish(BlockCipher::MODE_CBC);
             case 'blowfish-ctr':
-                return new Blowfish(Base::MODE_CTR);
+                return new Blowfish(BlockCipher::MODE_CTR);
             case 'twofish128-cbc':
             case 'twofish192-cbc':
             case 'twofish256-cbc':
             case 'twofish-cbc':
-                return new Twofish(Base::MODE_CBC);
+                return new Twofish(BlockCipher::MODE_CBC);
             case 'twofish128-ctr':
             case 'twofish192-ctr':
             case 'twofish256-ctr':
-                return new Twofish(Base::MODE_CTR);
+                return new Twofish(BlockCipher::MODE_CTR);
             case 'arcfour':
             case 'arcfour128':
             case 'arcfour256':
@@ -1940,7 +1941,7 @@ class SSH2
                 throw new \RuntimeException('Connection closed by server');
             }
 
-            extract(unpack('Ctype', $this->_string_shift($response, 1)));
+            extract(unpack('Ctype', Strings::shift($response, 1)));
 
             if ($type != NET_SSH2_MSG_SERVICE_ACCEPT) {
                 throw new \UnexpectedValueException('Expected SSH_MSG_SERVICE_ACCEPT');
@@ -1987,7 +1988,7 @@ class SSH2
                 throw new \RuntimeException('Connection closed by server');
             }
 
-            extract(unpack('Ctype', $this->_string_shift($response, 1)));
+            extract(unpack('Ctype', Strings::shift($response, 1)));
 
             switch ($type) {
                 case NET_SSH2_MSG_USERAUTH_SUCCESS:
@@ -2041,22 +2042,22 @@ class SSH2
             throw new \RuntimeException('Connection closed by server');
         }
 
-        extract(unpack('Ctype', $this->_string_shift($response, 1)));
+        extract(unpack('Ctype', Strings::shift($response, 1)));
 
         switch ($type) {
             case NET_SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ: // in theory, the password can be changed
                 if (defined('NET_SSH2_LOGGING')) {
                     $this->message_number_log[count($this->message_number_log) - 1] = 'NET_SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ';
                 }
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $this->errors[] = 'SSH_MSG_USERAUTH_PASSWD_CHANGEREQ: ' . utf8_decode($this->_string_shift($response, $length));
+                extract(unpack('Nlength', Strings::shift($response, 4)));
+                $this->errors[] = 'SSH_MSG_USERAUTH_PASSWD_CHANGEREQ: ' . utf8_decode(Strings::shift($response, $length));
                 return $this->_disconnect(NET_SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER);
             case NET_SSH2_MSG_USERAUTH_FAILURE:
                 // can we use keyboard-interactive authentication?  if not then either the login is bad or the server employees
                 // multi-factor authentication
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $auth_methods = explode(',', $this->_string_shift($response, $length));
-                extract(unpack('Cpartial_success', $this->_string_shift($response, 1)));
+                extract(unpack('Nlength', Strings::shift($response, 4)));
+                $auth_methods = explode(',', Strings::shift($response, $length));
+                extract(unpack('Cpartial_success', Strings::shift($response, 1)));
                 $partial_success = $partial_success != 0;
 
                 if (!$partial_success && in_array('keyboard-interactive', $auth_methods)) {
@@ -2130,17 +2131,17 @@ class SSH2
             }
         }
 
-        extract(unpack('Ctype', $this->_string_shift($response, 1)));
+        extract(unpack('Ctype', Strings::shift($response, 1)));
 
         switch ($type) {
             case NET_SSH2_MSG_USERAUTH_INFO_REQUEST:
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $this->_string_shift($response, $length); // name; may be empty
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $this->_string_shift($response, $length); // instruction; may be empty
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $this->_string_shift($response, $length); // language tag; may be empty
-                extract(unpack('Nnum_prompts', $this->_string_shift($response, 4)));
+                extract(unpack('Nlength', Strings::shift($response, 4)));
+                Strings::shift($response, $length); // name; may be empty
+                extract(unpack('Nlength', Strings::shift($response, 4)));
+                Strings::shift($response, $length); // instruction; may be empty
+                extract(unpack('Nlength', Strings::shift($response, 4)));
+                Strings::shift($response, $length); // language tag; may be empty
+                extract(unpack('Nnum_prompts', Strings::shift($response, 4)));
 
                 for ($i = 0; $i < count($responses); $i++) {
                     if (is_array($responses[$i])) {
@@ -2154,10 +2155,10 @@ class SSH2
 
                 if (isset($this->keyboard_requests_responses)) {
                     for ($i = 0; $i < $num_prompts; $i++) {
-                        extract(unpack('Nlength', $this->_string_shift($response, 4)));
+                        extract(unpack('Nlength', Strings::shift($response, 4)));
                         // prompt - ie. "Password: "; must not be empty
-                        $prompt = $this->_string_shift($response, $length);
-                        //$echo = $this->_string_shift($response) != chr(0);
+                        $prompt = Strings::shift($response, $length);
+                        //$echo = Strings::shift($response) != chr(0);
                         foreach ($this->keyboard_requests_responses as $key => $value) {
                             if (substr($prompt, 0, strlen($key)) == $key) {
                                 $responses[] = $value;
@@ -2299,12 +2300,12 @@ class SSH2
             throw new \RuntimeException('Connection closed by server');
         }
 
-        extract(unpack('Ctype', $this->_string_shift($response, 1)));
+        extract(unpack('Ctype', Strings::shift($response, 1)));
 
         switch ($type) {
             case NET_SSH2_MSG_USERAUTH_FAILURE:
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                $this->errors[] = 'SSH_MSG_USERAUTH_FAILURE: ' . $this->_string_shift($response, $length);
+                extract(unpack('Nlength', Strings::shift($response, 4)));
+                $this->errors[] = 'SSH_MSG_USERAUTH_FAILURE: ' . Strings::shift($response, $length);
                 return false;
             case NET_SSH2_MSG_USERAUTH_PK_OK:
                 // we'll just take it on faith that the public key blob and the public key algorithm name are as
@@ -2333,7 +2334,7 @@ class SSH2
             throw new \RuntimeException('Connection closed by server');
         }
 
-        extract(unpack('Ctype', $this->_string_shift($response, 1)));
+        extract(unpack('Ctype', Strings::shift($response, 1)));
 
         switch ($type) {
             case NET_SSH2_MSG_USERAUTH_FAILURE:
@@ -2451,7 +2452,7 @@ class SSH2
                 throw new \RuntimeException('Connection closed by server');
             }
 
-            list(, $type) = unpack('C', $this->_string_shift($response, 1));
+            list(, $type) = unpack('C', Strings::shift($response, 1));
 
             switch ($type) {
                 case NET_SSH2_MSG_CHANNEL_SUCCESS:
@@ -2588,7 +2589,7 @@ class SSH2
             throw new \RuntimeException('Connection closed by server');
         }
 
-        list(, $type) = unpack('C', $this->_string_shift($response, 1));
+        list(, $type) = unpack('C', Strings::shift($response, 1));
 
         switch ($type) {
             case NET_SSH2_MSG_CHANNEL_SUCCESS:
@@ -2700,12 +2701,12 @@ class SSH2
             }
             $pos = strlen($match) ? strpos($this->interactiveBuffer, $match) : false;
             if ($pos !== false) {
-                return $this->_string_shift($this->interactiveBuffer, $pos + strlen($match));
+                return Strings::shift($this->interactiveBuffer, $pos + strlen($match));
             }
             $response = $this->_get_channel_packet($channel);
             if (is_bool($response)) {
                 $this->in_request_pty_exec = false;
-                return $response ? $this->_string_shift($this->interactiveBuffer, strlen($this->interactiveBuffer)) : false;
+                return $response ? Strings::shift($this->interactiveBuffer, strlen($this->interactiveBuffer)) : false;
             }
 
             $this->interactiveBuffer.= $response;
@@ -2921,7 +2922,7 @@ class SSH2
             throw new \RuntimeException('Unable to decrypt content');
         }
 
-        extract(unpack('Npacket_length/Cpadding_length', $this->_string_shift($raw, 5)));
+        extract(unpack('Npacket_length/Cpadding_length', Strings::shift($raw, 5)));
 
         $remaining_length = $packet_length + 4 - $this->decrypt_block_size;
 
@@ -2947,8 +2948,8 @@ class SSH2
             $raw.= $this->decrypt !== false ? $this->decrypt->decrypt($buffer) : $buffer;
         }
 
-        $payload = $this->_string_shift($raw, $packet_length - $padding_length - 1);
-        $padding = $this->_string_shift($raw, $padding_length); // should leave $raw empty
+        $payload = Strings::shift($raw, $packet_length - $padding_length - 1);
+        $padding = Strings::shift($raw, $padding_length); // should leave $raw empty
 
         if ($this->hmac_check !== false) {
             $hmac = stream_get_contents($this->fsock, $this->hmac_size);
@@ -2991,18 +2992,18 @@ class SSH2
     {
         switch (ord($payload[0])) {
             case NET_SSH2_MSG_DISCONNECT:
-                $this->_string_shift($payload, 1);
-                extract(unpack('Nreason_code/Nlength', $this->_string_shift($payload, 8)));
-                $this->errors[] = 'SSH_MSG_DISCONNECT: ' . $this->disconnect_reasons[$reason_code] . "\r\n" . utf8_decode($this->_string_shift($payload, $length));
+                Strings::shift($payload, 1);
+                extract(unpack('Nreason_code/Nlength', Strings::shift($payload, 8)));
+                $this->errors[] = 'SSH_MSG_DISCONNECT: ' . $this->disconnect_reasons[$reason_code] . "\r\n" . utf8_decode(Strings::shift($payload, $length));
                 $this->bitmap = 0;
                 return false;
             case NET_SSH2_MSG_IGNORE:
                 $payload = $this->_get_binary_packet();
                 break;
             case NET_SSH2_MSG_DEBUG:
-                $this->_string_shift($payload, 2);
-                extract(unpack('Nlength', $this->_string_shift($payload, 4)));
-                $this->errors[] = 'SSH_MSG_DEBUG: ' . utf8_decode($this->_string_shift($payload, $length));
+                Strings::shift($payload, 2);
+                extract(unpack('Nlength', Strings::shift($payload, 4)));
+                $this->errors[] = 'SSH_MSG_DEBUG: ' . utf8_decode(Strings::shift($payload, $length));
                 $payload = $this->_get_binary_packet();
                 break;
             case NET_SSH2_MSG_UNIMPLEMENTED:
@@ -3019,9 +3020,9 @@ class SSH2
 
         // see http://tools.ietf.org/html/rfc4252#section-5.4; only called when the encryption has been activated and when we haven't already logged in
         if (($this->bitmap & self::MASK_CONNECTED) && !($this->bitmap & self::MASK_LOGIN) && ord($payload[0]) == NET_SSH2_MSG_USERAUTH_BANNER) {
-            $this->_string_shift($payload, 1);
-            extract(unpack('Nlength', $this->_string_shift($payload, 4)));
-            $this->banner_message = utf8_decode($this->_string_shift($payload, $length));
+            Strings::shift($payload, 1);
+            extract(unpack('Nlength', Strings::shift($payload, 4)));
+            $this->banner_message = utf8_decode(Strings::shift($payload, $length));
             $payload = $this->_get_binary_packet();
         }
 
@@ -3029,8 +3030,8 @@ class SSH2
         if (($this->bitmap & self::MASK_CONNECTED) && ($this->bitmap & self::MASK_LOGIN)) {
             switch (ord($payload[0])) {
                 case NET_SSH2_MSG_GLOBAL_REQUEST: // see http://tools.ietf.org/html/rfc4254#section-4
-                    extract(unpack('Nlength', $this->_string_shift($payload, 4)));
-                    $this->errors[] = 'SSH_MSG_GLOBAL_REQUEST: ' . $this->_string_shift($payload, $length);
+                    extract(unpack('Nlength', Strings::shift($payload, 4)));
+                    $this->errors[] = 'SSH_MSG_GLOBAL_REQUEST: ' . Strings::shift($payload, $length);
 
                     if (!$this->_send_binary_packet(pack('C', NET_SSH2_MSG_REQUEST_FAILURE))) {
                         return $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
@@ -3039,18 +3040,18 @@ class SSH2
                     $payload = $this->_get_binary_packet();
                     break;
                 case NET_SSH2_MSG_CHANNEL_OPEN: // see http://tools.ietf.org/html/rfc4254#section-5.1
-                    $this->_string_shift($payload, 1);
-                    extract(unpack('Nlength', $this->_string_shift($payload, 4)));
-                    $data = $this->_string_shift($payload, $length);
-                    extract(unpack('Nserver_channel', $this->_string_shift($payload, 4)));
+                    Strings::shift($payload, 1);
+                    extract(unpack('Nlength', Strings::shift($payload, 4)));
+                    $data = Strings::shift($payload, $length);
+                    extract(unpack('Nserver_channel', Strings::shift($payload, 4)));
                     switch ($data) {
                         case 'auth-agent':
                         case 'auth-agent@openssh.com':
                             if (isset($this->agent)) {
                                 $new_channel = self::CHANNEL_AGENT_FORWARD;
 
-                                extract(unpack('Nremote_window_size', $this->_string_shift($payload, 4)));
-                                extract(unpack('Nremote_maximum_packet_size', $this->_string_shift($payload, 4)));
+                                extract(unpack('Nremote_window_size', Strings::shift($payload, 4)));
+                                extract(unpack('Nremote_maximum_packet_size', Strings::shift($payload, 4)));
 
                                 $this->packet_size_client_to_server[$new_channel] = $remote_window_size;
                                 $this->window_size_server_to_client[$new_channel] = $remote_maximum_packet_size;
@@ -3093,9 +3094,9 @@ class SSH2
                     $payload = $this->_get_binary_packet();
                     break;
                 case NET_SSH2_MSG_CHANNEL_WINDOW_ADJUST:
-                    $this->_string_shift($payload, 1);
-                    extract(unpack('Nchannel', $this->_string_shift($payload, 4)));
-                    extract(unpack('Nwindow_size', $this->_string_shift($payload, 4)));
+                    Strings::shift($payload, 1);
+                    extract(unpack('Nchannel', Strings::shift($payload, 4)));
+                    extract(unpack('Nwindow_size', Strings::shift($payload, 4)));
                     $this->window_size_client_to_server[$channel]+= $window_size;
 
                     $payload = ($this->bitmap & self::MASK_WINDOW_ADJUST) ? true : $this->_get_binary_packet();
@@ -3224,12 +3225,12 @@ class SSH2
                 return '';
             }
 
-            extract(unpack('Ctype', $this->_string_shift($response, 1)));
+            extract(unpack('Ctype', Strings::shift($response, 1)));
 
             if ($type == NET_SSH2_MSG_CHANNEL_OPEN) {
-                extract(unpack('Nlength', $this->_string_shift($response, 4)));
+                extract(unpack('Nlength', Strings::shift($response, 4)));
             } else {
-                extract(unpack('Nchannel', $this->_string_shift($response, 4)));
+                extract(unpack('Nchannel', Strings::shift($response, 4)));
             }
 
             // will not be setup yet on incoming channel open request
@@ -3249,15 +3250,15 @@ class SSH2
                     case NET_SSH2_MSG_CHANNEL_OPEN:
                         switch ($type) {
                             case NET_SSH2_MSG_CHANNEL_OPEN_CONFIRMATION:
-                                extract(unpack('Nserver_channel', $this->_string_shift($response, 4)));
+                                extract(unpack('Nserver_channel', Strings::shift($response, 4)));
                                 $this->server_channels[$channel] = $server_channel;
-                                extract(unpack('Nwindow_size', $this->_string_shift($response, 4)));
+                                extract(unpack('Nwindow_size', Strings::shift($response, 4)));
                                 if ($window_size < 0) {
                                     $window_size&= 0x7FFFFFFF;
                                     $window_size+= 0x80000000;
                                 }
                                 $this->window_size_client_to_server[$channel] = $window_size;
-                                $temp = unpack('Npacket_size_client_to_server', $this->_string_shift($response, 4));
+                                $temp = unpack('Npacket_size_client_to_server', Strings::shift($response, 4));
                                 $this->packet_size_client_to_server[$channel] = $temp['packet_size_client_to_server'];
                                 $result = $client_channel == $channel ? true : $this->_get_channel_packet($client_channel, $skip_extended);
                                 $this->_on_channel_open();
@@ -3296,8 +3297,8 @@ class SSH2
                         $this->_send_channel_packet($channel, chr(0));
                     }
                     */
-                    extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                    $data = $this->_string_shift($response, $length);
+                    extract(unpack('Nlength', Strings::shift($response, 4)));
+                    $data = Strings::shift($response, $length);
 
                     if ($channel == self::CHANNEL_AGENT_FORWARD) {
                         $agent_response = $this->agent->_forward_data($data);
@@ -3322,8 +3323,8 @@ class SSH2
                     }
                     */
                     // currently, there's only one possible value for $data_type_code: NET_SSH2_EXTENDED_DATA_STDERR
-                    extract(unpack('Ndata_type_code/Nlength', $this->_string_shift($response, 8)));
-                    $data = $this->_string_shift($response, $length);
+                    extract(unpack('Ndata_type_code/Nlength', Strings::shift($response, 8)));
+                    $data = Strings::shift($response, $length);
                     $this->stdErrorLog.= $data;
                     if ($skip_extended || $this->quiet_mode) {
                         break;
@@ -3337,17 +3338,17 @@ class SSH2
                     $this->channel_buffers[$channel][] = $data;
                     break;
                 case NET_SSH2_MSG_CHANNEL_REQUEST:
-                    extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                    $value = $this->_string_shift($response, $length);
+                    extract(unpack('Nlength', Strings::shift($response, 4)));
+                    $value = Strings::shift($response, $length);
                     switch ($value) {
                         case 'exit-signal':
-                            $this->_string_shift($response, 1);
-                            extract(unpack('Nlength', $this->_string_shift($response, 4)));
-                            $this->errors[] = 'SSH_MSG_CHANNEL_REQUEST (exit-signal): ' . $this->_string_shift($response, $length);
-                            $this->_string_shift($response, 1);
-                            extract(unpack('Nlength', $this->_string_shift($response, 4)));
+                            Strings::shift($response, 1);
+                            extract(unpack('Nlength', Strings::shift($response, 4)));
+                            $this->errors[] = 'SSH_MSG_CHANNEL_REQUEST (exit-signal): ' . Strings::shift($response, $length);
+                            Strings::shift($response, 1);
+                            extract(unpack('Nlength', Strings::shift($response, 4)));
                             if ($length) {
-                                $this->errors[count($this->errors)].= "\r\n" . $this->_string_shift($response, $length);
+                                $this->errors[count($this->errors)].= "\r\n" . Strings::shift($response, $length);
                             }
 
                             $this->_send_binary_packet(pack('CN', NET_SSH2_MSG_CHANNEL_EOF, $this->server_channels[$client_channel]));
@@ -3357,7 +3358,7 @@ class SSH2
 
                             break;
                         case 'exit-status':
-                            extract(unpack('Cfalse/Nexit_status', $this->_string_shift($response, 5)));
+                            extract(unpack('Cfalse/Nexit_status', Strings::shift($response, 5)));
                             $this->exit_status = $exit_status;
 
                             // "The client MAY ignore these messages."
@@ -3465,7 +3466,7 @@ class SSH2
     {
         // remove the byte identifying the message type from all but the first two messages (ie. the identification strings)
         if (strlen($message_number) > 2) {
-            $this->_string_shift($message);
+            Strings::shift($message);
         }
 
         switch (NET_SSH2_LOGGING) {
@@ -3558,7 +3559,7 @@ class SSH2
                 $this->window_size_client_to_server[$client_channel]
             );
 
-            $temp = $this->_string_shift($data, $max_size);
+            $temp = Strings::shift($data, $max_size);
             $packet = pack(
                 'CN2a*',
                 NET_SSH2_MSG_CHANNEL_DATA,
@@ -3631,23 +3632,6 @@ class SSH2
         }
     }
 
-    /**
-     * String Shift
-     *
-     * Inspired by array_shift
-     *
-     * @param string $string
-     * @param int $index
-     * @return string
-     * @access private
-     */
-    function _string_shift(&$string, $index = 1)
-    {
-        $substr = substr($string, 0, $index);
-        $string = substr($string, $index);
-        return $substr;
-    }
-
     /**
      * Define Array
      *
@@ -3717,7 +3701,7 @@ class SSH2
                 if (strlen($current_log)) {
                     $output.= str_pad(dechex($j), 7, '0', STR_PAD_LEFT) . '0  ';
                 }
-                $fragment = $this->_string_shift($current_log, $this->log_short_width);
+                $fragment = Strings::shift($current_log, $this->log_short_width);
                 $hex = substr(preg_replace_callback('#.#s', array($this, '_format_log_helper'), $fragment), strlen($this->log_boundary));
                 // replace non ASCII printable characters with dots
                 // http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
@@ -3986,8 +3970,8 @@ class SSH2
         $signature = $this->signature;
         $server_public_host_key = $this->server_public_host_key;
 
-        extract(unpack('Nlength', $this->_string_shift($server_public_host_key, 4)));
-        $this->_string_shift($server_public_host_key, $length);
+        extract(unpack('Nlength', Strings::shift($server_public_host_key, 4)));
+        Strings::shift($server_public_host_key, $length);
 
         if ($this->signature_validated) {
             return $this->bitmap ?
@@ -4001,29 +3985,29 @@ class SSH2
             case 'ssh-dss':
                 $zero = new BigInteger();
 
-                $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-                $p = new BigInteger($this->_string_shift($server_public_host_key, $temp['length']), -256);
+                $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+                $p = new BigInteger(Strings::shift($server_public_host_key, $temp['length']), -256);
 
-                $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-                $q = new BigInteger($this->_string_shift($server_public_host_key, $temp['length']), -256);
+                $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+                $q = new BigInteger(Strings::shift($server_public_host_key, $temp['length']), -256);
 
-                $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-                $g = new BigInteger($this->_string_shift($server_public_host_key, $temp['length']), -256);
+                $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+                $g = new BigInteger(Strings::shift($server_public_host_key, $temp['length']), -256);
 
-                $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-                $y = new BigInteger($this->_string_shift($server_public_host_key, $temp['length']), -256);
+                $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+                $y = new BigInteger(Strings::shift($server_public_host_key, $temp['length']), -256);
 
                 /* The value for 'dss_signature_blob' is encoded as a string containing
                    r, followed by s (which are 160-bit integers, without lengths or
                    padding, unsigned, and in network byte order). */
-                $temp = unpack('Nlength', $this->_string_shift($signature, 4));
+                $temp = unpack('Nlength', Strings::shift($signature, 4));
                 if ($temp['length'] != 40) {
                     $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
                     throw new \RuntimeException('Invalid signature');
                 }
 
-                $r = new BigInteger($this->_string_shift($signature, 20), 256);
-                $s = new BigInteger($this->_string_shift($signature, 20), 256);
+                $r = new BigInteger(Strings::shift($signature, 20), 256);
+                $s = new BigInteger(Strings::shift($signature, 20), 256);
 
                 switch (true) {
                     case $r->equals($zero):
@@ -4056,17 +4040,17 @@ class SSH2
 
                 break;
             case 'ssh-rsa':
-                $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-                $e = new BigInteger($this->_string_shift($server_public_host_key, $temp['length']), -256);
+                $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+                $e = new BigInteger(Strings::shift($server_public_host_key, $temp['length']), -256);
 
-                $temp = unpack('Nlength', $this->_string_shift($server_public_host_key, 4));
-                $rawN = $this->_string_shift($server_public_host_key, $temp['length']);
+                $temp = unpack('Nlength', Strings::shift($server_public_host_key, 4));
+                $rawN = Strings::shift($server_public_host_key, $temp['length']);
                 $n = new BigInteger($rawN, -256);
                 $nLength = strlen(ltrim($rawN, "\0"));
 
                 /*
-                $temp = unpack('Nlength', $this->_string_shift($signature, 4));
-                $signature = $this->_string_shift($signature, $temp['length']);
+                $temp = unpack('Nlength', Strings::shift($signature, 4));
+                $signature = Strings::shift($signature, $temp['length']);
 
                 $rsa = new RSA();
                 $rsa->load(array('e' => $e, 'n' => $n), 'raw');
@@ -4077,8 +4061,8 @@ class SSH2
                 }
                 */
 
-                $temp = unpack('Nlength', $this->_string_shift($signature, 4));
-                $s = new BigInteger($this->_string_shift($signature, $temp['length']), 256);
+                $temp = unpack('Nlength', Strings::shift($signature, 4));
+                $s = new BigInteger(Strings::shift($signature, $temp['length']), 256);
 
                 // validate an RSA signature per "8.2 RSASSA-PKCS1-v1_5", "5.2.2 RSAVP1", and "9.1 EMSA-PSS" in the
                 // following URL:
diff --git a/phpseclib/System/SSH/Agent/Identity.php b/phpseclib/System/SSH/Agent/Identity.php
index 612c414e..636acde4 100644
--- a/phpseclib/System/SSH/Agent/Identity.php
+++ b/phpseclib/System/SSH/Agent/Identity.php
@@ -1,4 +1,5 @@
 <?php
+
 /**
  * Pure-PHP ssh-agent client.
  *
diff --git a/tests/Unit/Crypt/AES/InternalTest.php b/tests/Unit/Crypt/AES/InternalTest.php
index b0433e84..97c3e9d0 100644
--- a/tests/Unit/Crypt/AES/InternalTest.php
+++ b/tests/Unit/Crypt/AES/InternalTest.php
@@ -5,12 +5,12 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 
 class Unit_Crypt_AES_InternalTest extends Unit_Crypt_AES_TestCase
 {
     protected function setUp()
     {
-        $this->engine = Base::ENGINE_INTERNAL;
+        $this->engine = BlockCipher::ENGINE_INTERNAL;
     }
 }
diff --git a/tests/Unit/Crypt/AES/McryptTest.php b/tests/Unit/Crypt/AES/McryptTest.php
index ecd203c6..e4e6ac4d 100644
--- a/tests/Unit/Crypt/AES/McryptTest.php
+++ b/tests/Unit/Crypt/AES/McryptTest.php
@@ -5,12 +5,12 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 
 class Unit_Crypt_AES_McryptTest extends Unit_Crypt_AES_TestCase
 {
     protected function setUp()
     {
-        $this->engine = Base::ENGINE_MCRYPT;
+        $this->engine = BlockCipher::ENGINE_MCRYPT;
     }
 }
diff --git a/tests/Unit/Crypt/AES/OpenSSLTest.php b/tests/Unit/Crypt/AES/OpenSSLTest.php
index 211a0ea6..cb8b3a4a 100644
--- a/tests/Unit/Crypt/AES/OpenSSLTest.php
+++ b/tests/Unit/Crypt/AES/OpenSSLTest.php
@@ -5,12 +5,12 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 
 class Unit_Crypt_AES_OpenSSLTest extends Unit_Crypt_AES_TestCase
 {
     protected function setUp()
     {
-        $this->engine = Base::ENGINE_OPENSSL;
+        $this->engine = BlockCipher::ENGINE_OPENSSL;
     }
 }
diff --git a/tests/Unit/Crypt/AES/TestCase.php b/tests/Unit/Crypt/AES/TestCase.php
index d89516ea..35ce7c65 100644
--- a/tests/Unit/Crypt/AES/TestCase.php
+++ b/tests/Unit/Crypt/AES/TestCase.php
@@ -6,7 +6,7 @@
  */
 
 use phpseclib\Crypt\AES;
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\Rijndael;
 
 abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
@@ -18,10 +18,10 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
         if ($aes->getEngine() != $this->engine) {
             $engine = 'internal';
             switch ($this->engine) {
-                case Base::ENGINE_OPENSSL:
+                case BlockCipher::ENGINE_OPENSSL:
                     $engine = 'OpenSSL';
                     break;
-                case Base::ENGINE_MCRYPT:
+                case BlockCipher::ENGINE_MCRYPT:
                     $engine = 'mcrypt';
             }
             self::markTestSkipped('Unable to initialize ' . $engine . ' engine');
@@ -36,9 +36,9 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
     public function continuousBufferCombos()
     {
         $modes = array(
-            Base::MODE_CTR,
-            Base::MODE_OFB,
-            Base::MODE_CFB,
+            BlockCipher::MODE_CTR,
+            BlockCipher::MODE_OFB,
+            BlockCipher::MODE_CFB,
         );
         $plaintexts = array(
             '',
@@ -100,7 +100,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
         // this test case is from the following URL:
         // https://web.archive.org/web/20070209120224/http://fp.gladman.plus.com/cryptography_technology/rijndael/aesdvec.zip
 
-        $aes = new Rijndael(Base::MODE_CBC);
+        $aes = new Rijndael(BlockCipher::MODE_CBC);
         $aes->setPreferredEngine($this->engine);
         $aes->disablePadding();
         $aes->setKey(pack('H*', '2b7e151628aed2a6abf7158809cf4f3c762e7160')); // 160-bit key. Valid in Rijndael.
@@ -118,7 +118,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
     {
         // same as the above - just with a different ciphertext
 
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
         $aes->setPreferredEngine($this->engine);
         $aes->disablePadding();
         $aes->setKey(pack('H*', '2b7e151628aed2a6abf7158809cf4f3c762e7160')); // 160-bit key. supported by Rijndael - not AES
@@ -136,9 +136,9 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
     public function continuousBufferBatteryCombos()
     {
         $modes = array(
-            Base::MODE_CTR,
-            Base::MODE_OFB,
-            Base::MODE_CFB,
+            BlockCipher::MODE_CTR,
+            BlockCipher::MODE_OFB,
+            BlockCipher::MODE_CFB,
         );
 
         $combos = array(
@@ -267,7 +267,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
     // from http://csrc.nist.gov/groups/STM/cavp/documents/aes/AESAVS.pdf#page=16
     public function testGFSBox128()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
 
         $aes->setKey(pack('H*', '00000000000000000000000000000000'));
         $aes->setIV(pack('H*', '00000000000000000000000000000000'));
@@ -294,7 +294,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     public function testGFSBox192()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
 
         $aes->setKey(pack('H*', '000000000000000000000000000000000000000000000000'));
         $aes->setIV(pack('H*', '00000000000000000000000000000000'));
@@ -319,7 +319,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     public function testGFSBox256()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
 
         $aes->setKey(pack('H*', '00000000000000000000000000000000' . '00000000000000000000000000000000'));
         $aes->setIV(pack('H*', '00000000000000000000000000000000'));
@@ -342,13 +342,13 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     public function testGetKeyLengthDefault()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
         $this->assertSame($aes->getKeyLength(), 128);
     }
 
     public function testGetKeyLengthWith192BitKey()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
         $aes->setKey(str_repeat('a', 24));
         $this->assertSame($aes->getKeyLength(), 192);
     }
@@ -358,7 +358,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
      */
     public function testSetKeyLengthWithLargerKey()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
         $aes->setKeyLength(128);
         $aes->setKey(str_repeat('a', 24));
         $aes->setIV(str_repeat("\0", 16));
@@ -373,7 +373,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
      */
     public function testSetKeyLengthWithSmallerKey()
     {
-        $aes = new AES(Base::MODE_CBC);
+        $aes = new AES(BlockCipher::MODE_CBC);
         $aes->setKeyLength(256);
         $aes->setKey(str_repeat('a', 16));
         $aes->setIV(str_repeat("\0", 16));
diff --git a/tests/Unit/Crypt/BlowfishTest.php b/tests/Unit/Crypt/BlowfishTest.php
index 4d095664..a2800a72 100644
--- a/tests/Unit/Crypt/BlowfishTest.php
+++ b/tests/Unit/Crypt/BlowfishTest.php
@@ -5,7 +5,7 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\Blowfish;
 
 class Unit_Crypt_BlowfishTest extends PhpseclibTestCase
@@ -13,9 +13,9 @@ class Unit_Crypt_BlowfishTest extends PhpseclibTestCase
     public function engineVectors()
     {
         $engines = array(
-            Base::ENGINE_INTERNAL => 'internal',
-            Base::ENGINE_MCRYPT => 'mcrypt',
-            Base::ENGINE_OPENSSL => 'OpenSSL',
+            BlockCipher::ENGINE_INTERNAL => 'internal',
+            BlockCipher::ENGINE_MCRYPT => 'mcrypt',
+            BlockCipher::ENGINE_OPENSSL => 'OpenSSL',
         );
 
         // tests from https://www.schneier.com/code/vectors.txt
diff --git a/tests/Unit/Crypt/RC2Test.php b/tests/Unit/Crypt/RC2Test.php
index 93dbf458..c15a4208 100644
--- a/tests/Unit/Crypt/RC2Test.php
+++ b/tests/Unit/Crypt/RC2Test.php
@@ -5,15 +5,15 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\RC2;
 
 class Unit_Crypt_RC2Test extends PhpseclibTestCase
 {
     var $engines = array(
-        Base::ENGINE_INTERNAL => 'internal',
-        Base::ENGINE_MCRYPT => 'mcrypt',
-        Base::ENGINE_OPENSSL => 'OpenSSL',
+        BlockCipher::ENGINE_INTERNAL => 'internal',
+        BlockCipher::ENGINE_MCRYPT => 'mcrypt',
+        BlockCipher::ENGINE_OPENSSL => 'OpenSSL',
     );
 
     public function engineVectors()
@@ -45,7 +45,7 @@ class Unit_Crypt_RC2Test extends PhpseclibTestCase
     // this test is just confirming RC2's key expansion
     public function testEncryptPadding()
     {
-        $rc2 = new RC2(Base::MODE_ECB);
+        $rc2 = new RC2(BlockCipher::MODE_ECB);
 
         // unlike Crypt_AES / Crypt_Rijndael, when you tell Crypt_RC2 that the key length is 128-bits the key isn't null padded to that length.
         // instead, RC2 key expansion is used to extend it out to that length. this isn't done for AES / Rijndael since that doesn't define any
@@ -82,22 +82,22 @@ class Unit_Crypt_RC2Test extends PhpseclibTestCase
 
         $rc2->setKey(str_repeat('d', 16), 128);
 
-        $rc2->setPreferredEngine(Base::ENGINE_INTERNAL);
+        $rc2->setPreferredEngine(BlockCipher::ENGINE_INTERNAL);
         $internal = $rc2->encrypt('d');
 
         $result = pack('H*', 'e3b36057f4821346');
         $this->assertEquals($result, $internal, 'Failed asserting that the internal engine produced the correct result');
 
-        $rc2->setPreferredEngine(Base::ENGINE_MCRYPT);
-        if ($rc2->getEngine() == Base::ENGINE_MCRYPT) {
+        $rc2->setPreferredEngine(BlockCipher::ENGINE_MCRYPT);
+        if ($rc2->getEngine() == BlockCipher::ENGINE_MCRYPT) {
             $mcrypt = $rc2->encrypt('d');
             $this->assertEquals($result, $mcrypt, 'Failed asserting that the mcrypt engine produced the correct result');
         } else {
             self::markTestSkipped('Unable to initialize mcrypt engine');
         }
 
-        $rc2->setPreferredEngine(Base::ENGINE_OPENSSL);
-        if ($rc2->getEngine() == Base::ENGINE_OPENSSL) {
+        $rc2->setPreferredEngine(BlockCipher::ENGINE_OPENSSL);
+        if ($rc2->getEngine() == BlockCipher::ENGINE_OPENSSL) {
             $openssl = $rc2->encrypt('d');
             $this->assertEquals($result, $openssl,  'Failed asserting that the OpenSSL engine produced the correct result');
         } else {
diff --git a/tests/Unit/Crypt/RC4Test.php b/tests/Unit/Crypt/RC4Test.php
index 1a020ff8..a97b7d0a 100644
--- a/tests/Unit/Crypt/RC4Test.php
+++ b/tests/Unit/Crypt/RC4Test.php
@@ -5,7 +5,7 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\StreamCipher;
 use phpseclib\Crypt\RC4;
 
 class Unit_Crypt_RC4Test extends PhpseclibTestCase
@@ -13,9 +13,9 @@ class Unit_Crypt_RC4Test extends PhpseclibTestCase
     public function engineVectors()
     {
         $engines = array(
-            Base::ENGINE_INTERNAL => 'internal',
-            Base::ENGINE_MCRYPT => 'mcrypt',
-            Base::ENGINE_OPENSSL => 'OpenSSL',
+            StreamCipher::ENGINE_INTERNAL => 'internal',
+            StreamCipher::ENGINE_MCRYPT => 'mcrypt',
+            StreamCipher::ENGINE_OPENSSL => 'OpenSSL',
         );
         // tests from https://tools.ietf.org/html/rfc6229
         $tests = array(
diff --git a/tests/Unit/Crypt/TripleDESTest.php b/tests/Unit/Crypt/TripleDESTest.php
index 2ed8f321..99b2363b 100644
--- a/tests/Unit/Crypt/TripleDESTest.php
+++ b/tests/Unit/Crypt/TripleDESTest.php
@@ -5,15 +5,15 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\TripleDES;
 
 class Unit_Crypt_TripleDESTest extends PhpseclibTestCase
 {
     var $engines = array(
-        Base::ENGINE_INTERNAL => 'internal',
-        Base::ENGINE_MCRYPT => 'mcrypt',
-        Base::ENGINE_OPENSSL => 'OpenSSL',
+        BlockCipher::ENGINE_INTERNAL => 'internal',
+        BlockCipher::ENGINE_MCRYPT => 'mcrypt',
+        BlockCipher::ENGINE_OPENSSL => 'OpenSSL',
     );
 
     public function engineVectors()
@@ -120,9 +120,9 @@ class Unit_Crypt_TripleDESTest extends PhpseclibTestCase
     public function engineIVVectors()
     {
         $engines = array(
-            Base::ENGINE_INTERNAL => 'internal',
-            Base::ENGINE_MCRYPT => 'mcrypt',
-            Base::ENGINE_OPENSSL => 'OpenSSL',
+            BlockCipher::ENGINE_INTERNAL => 'internal',
+            BlockCipher::ENGINE_MCRYPT => 'mcrypt',
+            BlockCipher::ENGINE_OPENSSL => 'OpenSSL',
         );
 
         // tests from http://csrc.nist.gov/groups/STM/cavp/documents/des/DESMMT.pdf
diff --git a/tests/Unit/Crypt/TwofishTest.php b/tests/Unit/Crypt/TwofishTest.php
index d678c9e1..db3dbce4 100644
--- a/tests/Unit/Crypt/TwofishTest.php
+++ b/tests/Unit/Crypt/TwofishTest.php
@@ -5,7 +5,7 @@
  * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
  */
 
-use phpseclib\Crypt\Base;
+use phpseclib\Crypt\Common\BlockCipher;
 use phpseclib\Crypt\Twofish;
 
 class Unit_Crypt_TwofishTest extends PhpseclibTestCase
@@ -13,9 +13,9 @@ class Unit_Crypt_TwofishTest extends PhpseclibTestCase
     public function testVectors()
     {
         $engines = array(
-            Base::ENGINE_INTERNAL => 'internal',
-            Base::ENGINE_MCRYPT => 'mcrypt',
-            Base::ENGINE_OPENSSL => 'OpenSSL',
+            BlockCipher::ENGINE_INTERNAL => 'internal',
+            BlockCipher::ENGINE_MCRYPT => 'mcrypt',
+            BlockCipher::ENGINE_OPENSSL => 'OpenSSL',
         );
 
         foreach ($engines as $engine => $name) {