diff --git a/phpseclib/Crypt/AES.php b/phpseclib/Crypt/AES.php
index 7d8cb8b0..40e78ede 100644
--- a/phpseclib/Crypt/AES.php
+++ b/phpseclib/Crypt/AES.php
@@ -65,31 +65,32 @@ class AES extends Rijndael
      *
      * @see \phpseclib\Crypt\Rijndael::setBlockLength()
      * @access public
-     * @param int $length
+     * @throws \BadMethodCallException anytime it's called
      */
     function setBlockLength($length)
     {
-        return;
+        throw new \BadMethodCallException('The block length cannot be set for AES.');
     }
 
     /**
      * Sets the key length
      *
-     * Valid key lengths are 128, 192, and 256.  If the length is less than 128, it will be rounded up to
-     * 128.  If the length is greater than 128 and invalid, it will be rounded down to the closest valid amount.
+     * Valid key lengths are 128, 192, and 256.  Set the link to bool(false) to disable a fixed key length
      *
      * @see \phpseclib\Crypt\Rijndael:setKeyLength()
      * @access public
      * @param int $length
+     * @throws \LengthException if the key length isn't supported
      */
     function setKeyLength($length)
     {
         switch ($length) {
-            case 160:
-                $length = 192;
+            case 128:
+            case 192:
+            case 256:
                 break;
-            case 224:
-                $length = 256;
+            default:
+                throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported');
         }
         parent::setKeyLength($length);
     }
@@ -103,24 +104,19 @@ class AES extends Rijndael
      * @see setKeyLength()
      * @access public
      * @param string $key
+     * @throws \LengthException if the key length isn't supported
      */
     function setKey($key)
     {
-        parent::setKey($key);
-
-        if (!$this->explicit_key_length) {
-            $length = strlen($key);
-            switch (true) {
-                case $length <= 16:
-                    $this->key_length = 16;
-                    break;
-                case $length <= 24:
-                    $this->key_length = 24;
-                    break;
-                default:
-                    $this->key_length = 32;
-            }
-            $this->_setEngine();
+        switch (strlen($key)) {
+            case 16:
+            case 24:
+            case 32:
+                break;
+            default:
+                throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported');
         }
+
+        parent::setKey($key);
     }
 }
diff --git a/phpseclib/Crypt/Base.php b/phpseclib/Crypt/Base.php
index 7f1b37de..9ef68546 100644
--- a/phpseclib/Crypt/Base.php
+++ b/phpseclib/Crypt/Base.php
@@ -139,7 +139,7 @@ abstract class Base
      * @var string
      * @access private
      */
-    var $key = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
+    var $key = false;
 
     /**
      * The Initialization Vector
@@ -429,15 +429,6 @@ abstract class Base
      */
     var $openssl_options;
 
-    /**
-     * Has the key length explicitly been set or should it be derived from the key, itself?
-     *
-     * @see self::setKeyLength()
-     * @var bool
-     * @access private
-     */
-    var $explicit_key_length = false;
-
     /**
      * Don't truncate / null pad key
      *
@@ -448,9 +439,16 @@ abstract class Base
     var $skip_key_adjustment = false;
 
     /**
-     * Default Constructor.
+     * Has the key length explicitly been set or should it be derived from the key, itself?
      *
-     * Determines whether or not the mcrypt extension should be used.
+     * @see self::setKeyLength()
+     * @var bool
+     * @access private
+     */
+    var $explicit_key_length = false;
+
+    /**
+     * Default Constructor.
      *
      * $mode could be:
      *
@@ -464,32 +462,29 @@ abstract class Base
      *
      * - self::MODE_OFB
      *
-     * If not explicitly set, self::MODE_CBC will be used.
-     *
      * @param int $mode
      * @access public
+     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
      */
-    function __construct($mode = self::MODE_CBC)
+    function __construct($mode)
     {
         // $mode dependent settings
         switch ($mode) {
             case self::MODE_ECB:
+            case self::MODE_CBC:
                 $this->paddable = true;
-                $this->mode = self::MODE_ECB;
                 break;
             case self::MODE_CTR:
             case self::MODE_CFB:
             case self::MODE_OFB:
             case self::MODE_STREAM:
-                $this->mode = $mode;
+                $this->paddable = false;
                 break;
-            case self::MODE_CBC:
             default:
-                $this->paddable = true;
-                $this->mode = self::MODE_CBC;
+                throw new \InvalidArgumentException('No valid mode has been specified');
         }
 
-        $this->_setEngine();
+        $this->mode = $mode;
 
         // Determining whether inline crypting can be used by the cipher
         if ($this->use_inline_crypt !== false && function_exists('create_function')) {
@@ -504,14 +499,22 @@ abstract class Base
      *
      * @access public
      * @param string $iv
+     * @throws \LengthException if the IV length isn't equal to the block size
+     * @throws \InvalidArgumentException if an IV is provided when one shouldn't be
      * @internal Can be overwritten by a sub class, but does not have to be
      */
     function setIV($iv)
     {
-        switch ($this->mode) {
-            case self::MODE_ECB:
-            case self::MODE_STREAM:
-                return;
+        if ($this->mode == self::MODE_ECB) {
+            throw new \InvalidArgumentException('This mode does not require an IV.');
+        }
+
+        if ($this->mode == self::MODE_STREAM && $this->usesIV()) {
+            throw new \InvalidArgumentException('This algorithm does not use an IV.');
+        }
+
+        if (strlen($iv) != $this->block_size) {
+            throw new \LengthException('Received initialization vector of size ' . strlen($iv) . ', but size ' . $this->block_size . ' is required');
         }
 
         $this->iv = $iv;
@@ -519,18 +522,14 @@ abstract class Base
     }
 
     /**
-     * Sets the key length.
-     *
-     * Keys with explicitly set lengths need to be treated accordingly
+     * Returns whether or not the algorithm uses an IV
      *
      * @access public
-     * @param int $length
+     * @return bool
      */
-    function setKeyLength($length)
+    function usesIV()
     {
-        $this->explicit_key_length = true;
-        $this->changed = true;
-        $this->_setEngine();
+        return true;
     }
 
     /**
@@ -555,6 +554,24 @@ abstract class Base
         return $this->block_size << 3;
     }
 
+    /**
+     * Sets the key length.
+     *
+     * Keys with explicitly set lengths need to be treated accordingly
+     *
+     * @access public
+     * @param int $length
+     */
+    function setKeyLength($length)
+    {
+        $this->explicit_key_length = $length >> 3;
+
+        if (is_string($this->key) && strlen($this->key) != $this->explicit_key_length) {
+            $this->key = false;
+            throw new \LengthException('Key has already been set and is not ' .$this->explicit_key_length . ' bytes long');
+        }
+    }
+
     /**
      * Sets the key.
      *
@@ -571,12 +588,12 @@ abstract class Base
      */
     function setKey($key)
     {
-        if (!$this->explicit_key_length) {
-            $this->setKeyLength(strlen($key) << 3);
-            $this->explicit_key_length = false;
+        if ($this->explicit_key_length !== false && strlen($key) != $this->explicit_key_length) {
+            throw new \LengthException('Key length has already been set to ' . $this->explicit_key_length . ' bytes and this key is ' . strlen($key) . ' bytes');
         }
 
         $this->key = $key;
+        $this->key_length = strlen($key);
         $this->changed = true;
         $this->_setEngine();
     }
@@ -620,7 +637,8 @@ abstract class Base
                 if (isset($func_args[5])) {
                     $dkLen = $func_args[5];
                 } else {
-                    $dkLen = $method == 'pbkdf1' ? 2 * $this->key_length : $this->key_length;
+                    $key_length = $this->explicit_key_length !== false ? $this->explicit_key_length : $this->key_length;
+                    $dkLen = $method == 'pbkdf1' ? 2 * $key_length : $key_length;
                 }
 
                 switch (true) {
@@ -987,14 +1005,13 @@ abstract class Base
      * @access public
      * @param string $ciphertext
      * @return string $plaintext
+     * @throws \LengthException if we're inside a block cipher and the ciphertext length is not a multiple of the block size
      * @internal Could, but not must, extend by the child Crypt_* class
      */
     function decrypt($ciphertext)
     {
         if ($this->paddable) {
-            // we pad with chr(0) since that's what mcrypt_generic does.  to quote from {@link http://www.php.net/function.mcrypt-generic}:
-            // "The data is padded with "\0" to make sure the length of the data is n * blocksize."
-            $ciphertext = str_pad($ciphertext, strlen($ciphertext) + ($this->block_size - strlen($ciphertext) % $this->block_size) % $this->block_size, chr(0));
+            throw new \LengthException('The ciphertext length (' . strlen($ciphertext) . ') needs to be a multiple of the block size (' . $this->block_length . ')');
         }
 
         if ($this->engine === self::ENGINE_OPENSSL) {
@@ -1888,13 +1905,7 @@ abstract class Base
             throw new \UnexpectedValueException('No IV has been defined');
         }
 
-        // mcrypt's handling of invalid's $iv:
-        // $this->encryptIV = $this->decryptIV = strlen($this->iv) == $this->block_size ? $this->iv : str_repeat("\0", $this->block_size);
-        $this->encryptIV = $this->decryptIV = str_pad(substr($this->iv, 0, $this->block_size), $this->block_size, "\0");
-
-        if (!$this->skip_key_adjustment) {
-            $this->key = str_pad(substr($this->key, 0, $this->key_length), $this->key_length, "\0");
-        }
+        $this->encryptIV = $this->decryptIV = $this->iv;
     }
 
     /**
diff --git a/phpseclib/Crypt/Blowfish.php b/phpseclib/Crypt/Blowfish.php
index 3949e812..3500df59 100644
--- a/phpseclib/Crypt/Blowfish.php
+++ b/phpseclib/Crypt/Blowfish.php
@@ -283,6 +283,22 @@ class Blowfish extends Base
      */
     var $key_length = 16;
 
+    /**
+     * Default Constructor.
+     *
+     * @param int $mode
+     * @access public
+     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
+     */
+    function __construct($mode)
+    {
+        if ($mode == self::MODE_STREAM) {
+            throw new \InvalidArgumentException('Block ciphers cannot be ran in stream mode');
+        }
+
+        parent::__construct($mode);
+    }
+
     /**
      * Sets the key length.
      *
@@ -293,14 +309,12 @@ class Blowfish extends Base
      */
     function setKeyLength($length)
     {
-        if ($length < 32) {
-            $this->key_length = 7;
-        } elseif ($length > 448) {
-            $this->key_length = 56;
-        } else {
-            $this->key_length = $length >> 3;
+        if ($length < 32 || $length > 448) {
+                throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys of sizes between 32 and 448 bits are supported');
         }
 
+        $this->key_length = $length >> 3;
+
         parent::setKeyLength($length);
     }
 
diff --git a/phpseclib/Crypt/DES.php b/phpseclib/Crypt/DES.php
index ccd51102..14273d28 100644
--- a/phpseclib/Crypt/DES.php
+++ b/phpseclib/Crypt/DES.php
@@ -578,6 +578,22 @@ class DES extends Base
         0x00000820, 0x00020020, 0x08000000, 0x08020800
     );
 
+    /**
+     * Default Constructor.
+     *
+     * @param int $mode
+     * @access public
+     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
+     */
+    function __construct($mode)
+    {
+        if ($mode == self::MODE_STREAM) {
+            throw new \InvalidArgumentException('Block ciphers cannot be ran in stream mode');
+        }
+
+        parent::__construct($mode);
+    }
+
     /**
      * Test for engine validity
      *
@@ -603,24 +619,18 @@ class DES extends Base
     /**
      * Sets the key.
      *
-     * Keys can be of any length.  DES, itself, uses 64-bit keys (eg. strlen($key) == 8), however, we
-     * only use the first eight, if $key has more then eight characters in it, and pad $key with the
-     * null byte if it is less then eight characters long.
+     * Keys must be 64-bits long or 8 bytes long.
      *
      * DES also requires that every eighth bit be a parity bit, however, we'll ignore that.
      *
-     * If the key is not explicitly set, it'll be assumed to be all zero's.
-     *
      * @see \phpseclib\Crypt\Base::setKey()
      * @access public
      * @param string $key
      */
     function setKey($key)
     {
-        // We check/cut here only up to max length of the key.
-        // Key padding to the proper length will be done in _setupKey()
-        if (strlen($key) > $this->key_length_max) {
-            $key = substr($key, 0, $this->key_length_max);
+        if (!($this instanceof TripleDES) && strlen($key) != 8) {
+            throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of size 8 are supported');
         }
 
         // Sets the key
diff --git a/phpseclib/Crypt/RC2.php b/phpseclib/Crypt/RC2.php
index 82dcd335..72522923 100644
--- a/phpseclib/Crypt/RC2.php
+++ b/phpseclib/Crypt/RC2.php
@@ -259,6 +259,22 @@ class RC2 extends Base
         0x70, 0x02, 0xC2, 0x1E, 0xB8, 0x0A, 0xFC, 0xE6
     );
 
+    /**
+     * Default Constructor.
+     *
+     * @param int $mode
+     * @access public
+     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
+     */
+    function __construct($mode)
+    {
+        if ($mode == self::MODE_STREAM) {
+            throw new \InvalidArgumentException('Block ciphers cannot be ran in stream mode');
+        }
+
+        parent::__construct($mode);
+    }
+
     /**
      * Test for engine validity
      *
@@ -292,12 +308,15 @@ class RC2 extends Base
      *
      * @access public
      * @param int $length in bits
+     * @throws \LengthException if the key length isn't supported
      */
     function setKeyLength($length)
     {
-        if ($length >= 1 && $length <= 1024) {
-            $this->default_key_length = $length;
+        if ($length < 1 || $length > 1024) {
+            throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys between 1 and 1024 bits, inclusive, are supported');
         }
+
+        $this->default_key_length = $length;
     }
 
     /**
@@ -326,16 +345,20 @@ class RC2 extends Base
      * @access public
      * @param string $key
      * @param int $t1 optional Effective key length in bits.
+     * @throws \LengthException if the key length isn't supported
      */
-    function setKey($key, $t1 = 0)
+    function setKey($key, $t1 = false)
     {
         $this->orig_key = $key;
 
-        if ($t1 <= 0) {
+        if ($t1 === false) {
             $t1 = $this->default_key_length;
-        } elseif ($t1 > 1024) {
-            $t1 = 1024;
         }
+
+        if ($t1 < 1 || $t1 > 1024) {
+            throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys between 1 and 1024 bits, inclusive, are supported');
+        }
+
         $this->current_key_length = $t1;
         // Key byte count should be 1..128.
         $key = strlen($key) ? substr($key, 0, 128) : "\x00";
diff --git a/phpseclib/Crypt/RC4.php b/phpseclib/Crypt/RC4.php
index 05fff58e..a2cb80ab 100644
--- a/phpseclib/Crypt/RC4.php
+++ b/phpseclib/Crypt/RC4.php
@@ -121,8 +121,6 @@ class RC4 extends Base
     /**
      * Default Constructor.
      *
-     * Determines whether or not the mcrypt extension should be used.
-     *
      * @see \phpseclib\Crypt\Base::__construct()
      * @return \phpseclib\Crypt\RC4
      * @access public
@@ -165,26 +163,14 @@ class RC4 extends Base
     }
 
     /**
-     * Dummy function.
+     * RC4 does not use an IV
      *
-     * Some protocols, such as WEP, prepend an "initialization vector" to the key, effectively creating a new key [1].
-     * If you need to use an initialization vector in this manner, feel free to prepend it to the key, yourself, before
-     * calling setKey().
-     *
-     * [1] WEP's initialization vectors (IV's) are used in a somewhat insecure way.  Since, in that protocol,
-     * the IV's are relatively easy to predict, an attack described by
-     * {@link http://www.drizzle.com/~aboba/IEEE/rc4_ksaproc.pdf Scott Fluhrer, Itsik Mantin, and Adi Shamir}
-     * can be used to quickly guess at the rest of the key.  The following links elaborate:
-     *
-     * {@link http://www.rsa.com/rsalabs/node.asp?id=2009 http://www.rsa.com/rsalabs/node.asp?id=2009}
-     * {@link http://en.wikipedia.org/wiki/Related_key_attack http://en.wikipedia.org/wiki/Related_key_attack}
-     *
-     * @param string $iv
-     * @see self::setKey()
      * @access public
+     * @return bool
      */
-    function setIV($iv)
+    function usesIV()
     {
+        return false;
     }
 
     /**
@@ -194,20 +180,38 @@ class RC4 extends Base
      *
      * @access public
      * @param int $length
+     * @throws \LengthException if the key length is invalid
      */
     function setKeyLength($length)
     {
-        if ($length < 8) {
-            $this->key_length = 1;
-        } elseif ($length > 2048) {
-            $this->key_length = 248;
-        } else {
-            $this->key_length = $length >> 3;
+        if ($length < 8 || $length > 2048) {
+            throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys between 1 and 256 bytes are supported');
         }
 
+        $this->key_length = $length >> 3;
+
         parent::setKeyLength($length);
     }
 
+    /**
+     * Sets the key length
+     *
+     * Keys can be between 1 and 256 bytes long.
+     *
+     * @access public
+     * @param int $length
+     * @throws \LengthException if the key length is invalid
+     */
+    function setKey($key)
+    {
+        $length = strlen($key);
+        if ($length < 1 || $length > 256) {
+            throw new \LengthException('Key size of ' . $length . ' bytes is not supported by RC4. Keys must be between 1 and 256 bytes long');
+        }
+
+        parent::setKey($length);
+    }
+
     /**
      * Encrypts a message.
      *
diff --git a/phpseclib/Crypt/RSA/PKCS1.php b/phpseclib/Crypt/RSA/PKCS1.php
index 26291612..ae208d15 100644
--- a/phpseclib/Crypt/RSA/PKCS1.php
+++ b/phpseclib/Crypt/RSA/PKCS1.php
@@ -114,7 +114,7 @@ class PKCS1 extends PKCS
         if (!empty($password) || is_string($password)) {
             $cipher = self::getEncryptionObject(self::$defaultEncryptionAlgorithm);
             $iv = Random::string($cipher->getBlockLength() >> 3);
-            $cipher->setKey(self::generateSymmetricKey($password, $iv, $cipher->getKeyLength()));
+            $cipher->setKey(self::generateSymmetricKey($password, $iv, $cipher->getKeyLength() >> 3));
             $cipher->setIV($iv);
             $iv = strtoupper(bin2hex($iv));
             $RSAPrivateKey = "-----BEGIN RSA PRIVATE KEY-----\r\n" .
diff --git a/phpseclib/Crypt/Rijndael.php b/phpseclib/Crypt/Rijndael.php
index 3648a197..c98f02e2 100644
--- a/phpseclib/Crypt/Rijndael.php
+++ b/phpseclib/Crypt/Rijndael.php
@@ -168,11 +168,26 @@ class Rijndael extends Base
      */
     var $kl;
 
+    /**
+     * Default Constructor.
+     *
+     * @param int $mode
+     * @access public
+     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
+     */
+    function __construct($mode)
+    {
+        if ($mode == self::MODE_STREAM) {
+            throw new \InvalidArgumentException('Block ciphers cannot be ran in stream mode');
+        }
+
+        parent::__construct($mode);
+    }
+
     /**
      * Sets the key length.
      *
-     * Valid key lengths are 128, 160, 192, 224, and 256.  If the length is less than 128, it will be rounded up to
-     * 128.  If the length is greater than 128 and invalid, it will be rounded down to the closest valid amount.
+     * Valid key lengths are 128, 160, 192, 224, and 256.
      *
      * Note: phpseclib extends Rijndael (and AES) for using 160- and 224-bit keys but they are officially not defined
      *       and the most (if not all) implementations are not able using 160/224-bit keys but round/pad them up to
@@ -186,49 +201,75 @@ class Rijndael extends Base
      *             This results then in slower encryption.
      *
      * @access public
+     * @throws \LengthException if the key length is invalid
      * @param int $length
      */
     function setKeyLength($length)
     {
-        switch (true) {
-            case $length <= 128:
-                $this->key_length = 16;
-                break;
-            case $length <= 160:
-                $this->key_length = 20;
-                break;
-            case $length <= 192:
-                $this->key_length = 24;
-                break;
-            case $length <= 224:
-                $this->key_length = 28;
+        switch ($length) {
+            case 128:
+            case 160:
+            case 192:
+            case 224:
+            case 256:
+                $this->key_length = $length >> 3;
                 break;
             default:
-                $this->key_length = 32;
+                throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys of sizes 128, 160, 192, 224 or 256 bits are supported');
         }
 
         parent::setKeyLength($length);
     }
 
+    /**
+     * Sets the key.
+     *
+     * Rijndael supports five different key lengths
+     *
+     * @see setKeyLength()
+     * @access public
+     * @param string $key
+     * @throws \LengthException if the key length isn't supported
+     */
+    function setKey($key)
+    {
+        switch (strlen($key)) {
+            case 16:
+            case 20:
+            case 24:
+            case 28:
+            case 32:
+                break;
+            default:
+                throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16, 20, 24, 28 or 32 are supported');
+        }
+
+        parent::setKey($key);
+    }
+
     /**
      * Sets the block length
      *
-     * Valid block lengths are 128, 160, 192, 224, and 256.  If the length is less than 128, it will be rounded up to
-     * 128.  If the length is greater than 128 and invalid, it will be rounded down to the closest valid amount.
+     * Valid block lengths are 128, 160, 192, 224, and 256.
      *
      * @access public
      * @param int $length
      */
     function setBlockLength($length)
     {
-        $length >>= 5;
-        if ($length > 8) {
-            $length = 8;
-        } elseif ($length < 4) {
-            $length = 4;
+        switch ($length) {
+            case 128:
+            case 160:
+            case 192:
+            case 224:
+            case 256:
+                break;
+            default:
+                throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys of sizes 128, 160, 192, 224 or 256 bits are supported');
         }
-        $this->Nb = $length;
-        $this->block_size = $length << 2;
+
+        $this->Nb = $length >> 5;
+        $this->block_size = $length >> 3;
         $this->changed = true;
         $this->_setEngine();
     }
diff --git a/phpseclib/Crypt/TripleDES.php b/phpseclib/Crypt/TripleDES.php
index a2c41668..3772cf3d 100644
--- a/phpseclib/Crypt/TripleDES.php
+++ b/phpseclib/Crypt/TripleDES.php
@@ -128,7 +128,7 @@ class TripleDES extends DES
     /**
      * Default Constructor.
      *
-     * Determines whether or not the mcrypt extension should be used.
+     * Determines whether or not the mcrypt or OpenSSL extensions should be used.
      *
      * $mode could be:
      *
@@ -142,16 +142,14 @@ class TripleDES extends DES
      *
      * - \phpseclib\Crypt\Base::MODE_OFB
      *
-     * - \phpseclib\Crypt\TripleDES::MODE_3CBC
-     *
-     * If not explicitly set, \phpseclib\Crypt\Base::MODE_CBC will be used.
+     * - \phpseclib\Crypt\TripleDES::MODE_3CB
      *
      * @see \phpseclib\Crypt\DES::__construct()
      * @see \phpseclib\Crypt\Base::__construct()
      * @param int $mode
      * @access public
      */
-    function __construct($mode = Base::MODE_CBC)
+    function __construct($mode)
     {
         switch ($mode) {
             // In case of self::MODE_3CBC, we init as CRYPT_DES_MODE_CBC
@@ -200,10 +198,9 @@ class TripleDES extends DES
     }
 
     /**
-     * Sets the initialization vector. (optional)
+     * Sets the initialization vector.
      *
-     * SetIV is not required when \phpseclib\Crypt\Base::MODE_ECB is being used.  If not explicitly set, it'll be assumed
-     * to be all zero's.
+     * SetIV is not required when \phpseclib\Crypt\Base::MODE_ECB is being used.
      *
      * @see \phpseclib\Crypt\Base::setIV()
      * @access public
@@ -222,24 +219,23 @@ class TripleDES extends DES
     /**
      * Sets the key length.
      *
-     * Valid key lengths are 64, 128 and 192
+     * Valid key lengths are 128 and 192 bits.
+     *
+     * If you want to use a 64-bit key use DES.php
      *
      * @see \phpseclib\Crypt\Base:setKeyLength()
      * @access public
+     * @throws \LengthException if the key length is invalid
      * @param int $length
      */
     function setKeyLength($length)
     {
-        $length >>= 3;
-        switch (true) {
-            case $length <= 8:
-                $this->key_length = 8;
-                break;
-            case $length <= 16:
-                $this->key_length = 16;
+        switch ($length) {
+            case 128:
+            case 192:
                 break;
             default:
-                $this->key_length = 24;
+                throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys of sizes 128 or 192 bits are supported');
         }
 
         parent::setKeyLength($length);
@@ -248,35 +244,37 @@ class TripleDES extends DES
     /**
      * Sets the key.
      *
-     * Keys can be of any length.  Triple DES, itself, can use 128-bit (eg. strlen($key) == 16) or
-     * 192-bit (eg. strlen($key) == 24) keys.  This function pads and truncates $key as appropriate.
+     * Triple DES can use 128-bit (eg. strlen($key) == 16) or 192-bit (eg. strlen($key) == 24) keys.
      *
      * DES also requires that every eighth bit be a parity bit, however, we'll ignore that.
      *
-     * If the key is not explicitly set, it'll be assumed to be all null bytes.
-     *
      * @access public
      * @see \phpseclib\Crypt\DES::setKey()
      * @see \phpseclib\Crypt\Base::setKey()
+     * @throws \LengthException if the key length is invalid
      * @param string $key
      */
     function setKey($key)
     {
-        $length = $this->explicit_key_length ? $this->key_length : strlen($key);
-        if ($length > 8) {
-            $key = str_pad(substr($key, 0, 24), 24, chr(0));
-            // if $key is between 64 and 128-bits, use the first 64-bits as the last, per this:
-            // http://php.net/function.mcrypt-encrypt#47973
-            $key = $length <= 16 ? substr_replace($key, substr($key, 0, 8), 16) : substr($key, 0, 24);
-        } else {
-            $key = str_pad($key, 8, chr(0));
+        if ($this->explicit_key_length !== false && strlen($key) != $this->explicit_key_length) {
+            throw new \LengthException('Key length has already been set to ' . $this->explicit_key_length . ' bytes and this key is ' . strlen($key) . ' bytes');
         }
-        parent::setKey($key);
 
-        // And in case of self::MODE_3CBC:
-        // if key <= 64bits we not need the 3 $des to work,
-        // because we will then act as regular DES-CBC with just a <= 64bit key.
-        // So only if the key > 64bits (> 8 bytes) we will call setKey() for the 3 $des.
+        switch (strlen($key)) {
+            case 16:
+                $key.= substr($key, 0, 8);
+            case 24:
+                break;
+            default:
+                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()
+        $this->key = $key;
+        $this->key_length = strlen($key);
+        $this->changed = true;
+        $this->_setEngine();
+
         if ($this->mode_3cbc && $length > 8) {
             $this->des[0]->setKey(substr($key,  0, 8));
             $this->des[1]->setKey(substr($key,  8, 8));
diff --git a/phpseclib/Crypt/Twofish.php b/phpseclib/Crypt/Twofish.php
index ef71a54c..e4d910db 100644
--- a/phpseclib/Crypt/Twofish.php
+++ b/phpseclib/Crypt/Twofish.php
@@ -368,6 +368,22 @@ class Twofish extends Base
      */
     var $key_length = 16;
 
+    /**
+     * Default Constructor.
+     *
+     * @param int $mode
+     * @access public
+     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
+     */
+    function __construct($mode)
+    {
+        if ($mode == self::MODE_STREAM) {
+            throw new \InvalidArgumentException('Block ciphers cannot be ran in stream mode');
+        }
+
+        parent::__construct($mode);
+    }
+
     /**
      * Sets the key length.
      *
@@ -378,20 +394,42 @@ class Twofish extends Base
      */
     function setKeyLength($length)
     {
-        switch (true) {
-            case $length <= 128:
-                $this->key_length = 16;
-                break;
-            case $length <= 192:
-                $this->key_length = 24;
+        switch ($length) {
+            case 128:
+            case 192:
+            case 256:
                 break;
             default:
-                $this->key_length = 32;
+                throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported');
         }
 
         parent::setKeyLength($length);
     }
 
+    /**
+     * Sets the key.
+     *
+     * Rijndael supports five different key lengths
+     *
+     * @see setKeyLength()
+     * @access public
+     * @param string $key
+     * @throws \LengthException if the key length isn't supported
+     */
+    function setKey($key)
+    {
+        switch (strlen($key)) {
+            case 16:
+            case 24:
+            case 32:
+                break;
+            default:
+                throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes 16, 24 or 32 supported');
+        }
+
+        parent::setKey($key);
+    }
+
     /**
      * Setup the key (expansion)
      *
diff --git a/phpseclib/Net/SSH1.php b/phpseclib/Net/SSH1.php
index 44cbe803..5379baaf 100644
--- a/phpseclib/Net/SSH1.php
+++ b/phpseclib/Net/SSH1.php
@@ -658,16 +658,18 @@ class SSH1
             //    $this->crypto = new \phpseclib\Crypt\Null();
             //    break;
             case self::CIPHER_DES:
-                $this->crypto = new DES();
+                $this->crypto = new DES(DES::MODE_CBC);
                 $this->crypto->disablePadding();
                 $this->crypto->enableContinuousBuffer();
                 $this->crypto->setKey(substr($session_key, 0,  8));
+                $this->crypto->setIV(str_repeat("\0", 8));
                 break;
             case self::CIPHER_3DES:
                 $this->crypto = new TripleDES(TripleDES::MODE_3CBC);
                 $this->crypto->disablePadding();
                 $this->crypto->enableContinuousBuffer();
                 $this->crypto->setKey(substr($session_key, 0, 24));
+                $this->crypto->setIV(str_repeat("\0", 8));
                 break;
             //case self::CIPHER_RC4:
             //    $this->crypto = new RC4();
diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index 55ede0a1..fe9d15b5 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -1616,11 +1616,13 @@ class SSH2
             $this->encrypt->enableContinuousBuffer();
             $this->encrypt->disablePadding();
 
-            $iv = $kexHash->hash($keyBytes . $this->exchange_hash . 'A' . $this->session_id);
-            while ($this->encrypt_block_size > strlen($iv)) {
-                $iv.= $kexHash->hash($keyBytes . $this->exchange_hash . $iv);
+            if ($this->encrypt->usesIV()) {
+                $iv = $kexHash->hash($keyBytes . $this->exchange_hash . 'A' . $this->session_id);
+                while ($this->encrypt_block_size > strlen($iv)) {
+                    $iv.= $kexHash->hash($keyBytes . $this->exchange_hash . $iv);
+                }
+                $this->encrypt->setIV(substr($iv, 0, $this->encrypt_block_size));
             }
-            $this->encrypt->setIV(substr($iv, 0, $this->encrypt_block_size));
 
             $key = $kexHash->hash($keyBytes . $this->exchange_hash . 'C' . $this->session_id);
             while ($encryptKeyLength > strlen($key)) {
@@ -1640,11 +1642,13 @@ class SSH2
             $this->decrypt->enableContinuousBuffer();
             $this->decrypt->disablePadding();
 
-            $iv = $kexHash->hash($keyBytes . $this->exchange_hash . 'B' . $this->session_id);
-            while ($this->decrypt_block_size > strlen($iv)) {
-                $iv.= $kexHash->hash($keyBytes . $this->exchange_hash . $iv);
+            if ($this->decrypt->usesIV()) {
+                $iv = $kexHash->hash($keyBytes . $this->exchange_hash . 'B' . $this->session_id);
+                while ($this->decrypt_block_size > strlen($iv)) {
+                    $iv.= $kexHash->hash($keyBytes . $this->exchange_hash . $iv);
+                }
+                $this->decrypt->setIV(substr($iv, 0, $this->decrypt_block_size));
             }
-            $this->decrypt->setIV(substr($iv, 0, $this->decrypt_block_size));
 
             $key = $kexHash->hash($keyBytes . $this->exchange_hash . 'D' . $this->session_id);
             while ($decryptKeyLength > strlen($key)) {
diff --git a/tests/Unit/Crypt/AES/TestCase.php b/tests/Unit/Crypt/AES/TestCase.php
index 4feb6f0e..0550b4e2 100644
--- a/tests/Unit/Crypt/AES/TestCase.php
+++ b/tests/Unit/Crypt/AES/TestCase.php
@@ -47,13 +47,13 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
             ':-):-):-):-):-):-)', // https://github.com/phpseclib/phpseclib/pull/43
         );
         $ivs = array(
-            '',
-            'test123',
+            str_repeat("\0", 16),
+            str_pad('test123', 16, "\0"),
         );
         $keys = array(
-            '',
-            ':-8', // https://github.com/phpseclib/phpseclib/pull/43
-            'FOOBARZ',
+            str_repeat("\0", 16),
+            str_pad(':-8', 16, "\0"), // https://github.com/phpseclib/phpseclib/pull/43
+            str_pad('FOOBARZ', 16, "\0"),
         );
 
         $result = 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();
+        $aes = new Rijndael(Base::MODE_CBC);
         $aes->setPreferredEngine($this->engine);
         $aes->disablePadding();
         $aes->setKey(pack('H*', '2b7e151628aed2a6abf7158809cf4f3c762e7160')); // 160-bit key. Valid in Rijndael.
@@ -112,15 +112,16 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     /**
      * @group github451
+     * @expectedException \LengthException
      */
     public function testKeyPaddingAES()
     {
         // same as the above - just with a different ciphertext
 
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
         $aes->setPreferredEngine($this->engine);
         $aes->disablePadding();
-        $aes->setKey(pack('H*', '2b7e151628aed2a6abf7158809cf4f3c762e7160')); // 160-bit key. AES should null pad to 192-bits
+        $aes->setKey(pack('H*', '2b7e151628aed2a6abf7158809cf4f3c762e7160')); // 160-bit key. supported by Rijndael - not AES
         $aes->setIV(str_repeat("\0", 16));
         $this->_checkEngine($aes);
         $ciphertext = $aes->encrypt(pack('H*', '3243f6a8885a308d313198a2e0370734'));
@@ -266,7 +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();
+        $aes = new AES(Base::MODE_CBC);
 
         $aes->setKey(pack('H*', '00000000000000000000000000000000'));
         $aes->setIV(pack('H*', '00000000000000000000000000000000'));
@@ -293,7 +294,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     public function testGFSBox192()
     {
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
 
         $aes->setKey(pack('H*', '000000000000000000000000000000000000000000000000'));
         $aes->setIV(pack('H*', '00000000000000000000000000000000'));
@@ -318,7 +319,7 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     public function testGFSBox256()
     {
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
 
         $aes->setKey(pack('H*', '00000000000000000000000000000000' . '00000000000000000000000000000000'));
         $aes->setIV(pack('H*', '00000000000000000000000000000000'));
@@ -341,20 +342,23 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
 
     public function testGetKeyLengthDefault()
     {
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
         $this->assertSame($aes->getKeyLength(), 128);
     }
 
     public function testGetKeyLengthWith192BitKey()
     {
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
         $aes->setKey(str_repeat('a', 24));
         $this->assertSame($aes->getKeyLength(), 192);
     }
 
+    /**
+     * @expectedException \LengthException
+     */
     public function testSetKeyLengthWithLargerKey()
     {
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
         $aes->setKeyLength(128);
         $aes->setKey(str_repeat('a', 24));
         $aes->setIV(str_repeat("\0", 16));
@@ -364,9 +368,12 @@ abstract class Unit_Crypt_AES_TestCase extends PhpseclibTestCase
         $this->assertSame($aes->getKeyLength(), 128);
     }
 
+    /**
+     * @expectedException \LengthException
+     */
     public function testSetKeyLengthWithSmallerKey()
     {
-        $aes = new AES();
+        $aes = new AES(Base::MODE_CBC);
         $aes->setKeyLength(256);
         $aes->setKey(str_repeat('a', 16));
         $aes->setIV(str_repeat("\0", 16));
diff --git a/tests/Unit/Crypt/BlowfishTest.php b/tests/Unit/Crypt/BlowfishTest.php
index f5b45a42..4d095664 100644
--- a/tests/Unit/Crypt/BlowfishTest.php
+++ b/tests/Unit/Crypt/BlowfishTest.php
@@ -73,7 +73,7 @@ class Unit_Crypt_BlowfishTest extends PhpseclibTestCase
      */
     public function testVectors($engine, $engineName, $key, $plaintext, $expected)
     {
-        $bf = new Blowfish();
+        $bf = new Blowfish(Blowfish::MODE_CBC);
         $bf->setKey($key);
         $bf->setIV(str_repeat("\0", $bf->getBlockLength() >> 3));
         if (!$bf->isValidEngine($engine)) {
diff --git a/tests/Unit/Crypt/DESTest.php b/tests/Unit/Crypt/DESTest.php
deleted file mode 100644
index 1f0eda9f..00000000
--- a/tests/Unit/Crypt/DESTest.php
+++ /dev/null
@@ -1,78 +0,0 @@
-<?php
-/**
- * @author    Andreas Fischer <bantu@phpbb.com>
- * @copyright MMXIII Andreas Fischer
- * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
- */
-
-use phpseclib\Crypt\Base;
-use phpseclib\Crypt\DES;
-
-// the AES tests establish the correctness of the modes of operation. this test is inteded to establish the consistency of
-// key and iv padding between the multiple engines
-class Unit_Crypt_DESTest extends PhpseclibTestCase
-{
-    public function testEncryptPadding()
-    {
-        $des = new DES(Base::MODE_CBC);
-        $des->setKey('d');
-        $des->setIV('d');
-
-        $des->setPreferredEngine(Base::ENGINE_INTERNAL);
-
-        $result = pack('H*', '3e7613642049af1e');
-
-        $internal = $des->encrypt('d');
-        $this->assertEquals($result, $internal, 'Failed asserting that the internal engine produced the correct result');
-
-        $des->setPreferredEngine(Base::ENGINE_MCRYPT);
-        if ($des->getEngine() == Base::ENGINE_MCRYPT) {
-            $mcrypt = $des->encrypt('d');
-            $this->assertEquals($result, $mcrypt, 'Failed asserting that the mcrypt engine produced the correct result');
-        } else {
-            self::markTestSkipped('Unable to initialize mcrypt engine');
-        }
-
-        $des->setPreferredEngine(Base::ENGINE_OPENSSL);
-        if ($des->getEngine() == Base::ENGINE_OPENSSL) {
-            $openssl = $des->encrypt('d');
-            $this->assertEquals($result, $openssl,  'Failed asserting that the OpenSSL engine produced the correct result');
-        } else {
-            self::markTestSkipped('Unable to initialize OpenSSL engine');
-        }
-    }
-
-    // phpseclib null pads ciphertext's if they're not long enough and you're in ecb / cbc mode. this silent failure mode is consistent
-    // with mcrypt's behavior. maybe throwing an exception would be better but whatever. this test is more intended to establish consistent
-    // behavior between the various engine's
-    public function testDecryptPadding()
-    {
-        $des = new DES(Base::MODE_CBC);
-        $des->disablePadding();
-        // when the key and iv are not specified they should be null padded
-        //$des->setKey();
-        $des->setIV('');
-
-        $des->setPreferredEngine(Base::ENGINE_INTERNAL);
-        $internal = $des->decrypt('d');
-
-        $result = pack('H*', '79b305d1ce555221');
-        $this->assertEquals($result, $internal, 'Failed asserting that the internal engine produced the correct result');
-
-        $des->setPreferredEngine(Base::ENGINE_MCRYPT);
-        if ($des->getEngine() == Base::ENGINE_MCRYPT) {
-            $mcrypt = $des->decrypt('d');
-            $this->assertEquals($result, $mcrypt, 'Failed asserting that the mcrypt engine produced the correct result');
-        } else {
-            self::markTestSkipped('Unable to initialize mcrypt engine');
-        }
-
-        $des->setPreferredEngine(Base::ENGINE_OPENSSL);
-        if ($des->getEngine() == Base::ENGINE_OPENSSL) {
-            $openssl = $des->decrypt('d');
-            $this->assertEquals($result, $openssl,  'Failed asserting that the OpenSSL engine produced the correct result');
-        } else {
-            self::markTestSkipped('Unable to initialize OpenSSL engine');
-        }
-    }
-}
diff --git a/tests/Unit/Crypt/RC2Test.php b/tests/Unit/Crypt/RC2Test.php
index b6c3e463..93dbf458 100644
--- a/tests/Unit/Crypt/RC2Test.php
+++ b/tests/Unit/Crypt/RC2Test.php
@@ -110,7 +110,7 @@ class Unit_Crypt_RC2Test extends PhpseclibTestCase
      */
     public function testVectors($engine, $engineName, $key, $keyLen, $plaintext, $ciphertext)
     {
-        $rc2 = new RC2();
+        $rc2 = new RC2(RC2::MODE_CBC);
         $rc2->disablePadding();
         $rc2->setKeyLength($keyLen);
         $rc2->setKey(pack('H*', $key)); // could also do $rc2->setKey(pack('H*', $key), $keyLen)
diff --git a/tests/Unit/Crypt/TripleDESTest.php b/tests/Unit/Crypt/TripleDESTest.php
index e2de3f2f..2ed8f321 100644
--- a/tests/Unit/Crypt/TripleDESTest.php
+++ b/tests/Unit/Crypt/TripleDESTest.php
@@ -104,7 +104,7 @@ class Unit_Crypt_TripleDESTest extends PhpseclibTestCase
      */
     public function testVectors($engine, $engineName, $key, $plaintext, $expected)
     {
-        $des = new TripleDES();
+        $des = new TripleDES(TripleDES::MODE_CBC);
         if (!$des->isValidEngine($engine)) {
             self::markTestSkipped('Unable to initialize ' . $engineName . ' engine');
         }
@@ -156,7 +156,7 @@ class Unit_Crypt_TripleDESTest extends PhpseclibTestCase
      */
     public function testVectorsWithIV($engine, $engineName, $key, $iv, $plaintext, $expected)
     {
-        $des = new TripleDES();
+        $des = new TripleDES(TripleDES::MODE_CBC);
         if (!$des->isValidEngine($engine)) {
             self::markTestSkipped('Unable to initialize ' . $engineName . ' engine');
         }
diff --git a/tests/Unit/Crypt/TwofishTest.php b/tests/Unit/Crypt/TwofishTest.php
index 6ebd84b1..d678c9e1 100644
--- a/tests/Unit/Crypt/TwofishTest.php
+++ b/tests/Unit/Crypt/TwofishTest.php
@@ -19,7 +19,7 @@ class Unit_Crypt_TwofishTest extends PhpseclibTestCase
         );
 
         foreach ($engines as $engine => $name) {
-            $tf = new Twofish();
+            $tf = new Twofish(Twofish::MODE_CBC);
             $tf->setIV(str_repeat("\0", $tf->getBlockLength() >> 3));
             $tf->disablePadding();