diff --git a/phpseclib/Crypt/Base.php b/phpseclib/Crypt/Base.php
index 715ab2a5..7096b662 100644
--- a/phpseclib/Crypt/Base.php
+++ b/phpseclib/Crypt/Base.php
@@ -545,6 +545,7 @@ abstract class Base
      * @see Crypt/Hash.php
      * @param String $password
      * @param optional String $method
+     * @throws \LengthException if pbkdf1 is being used and the derived key length exceeds the hash length
      * @return Boolean
      * @access public
      * @internal Could, but not must, extend by the child Crypt_* class
@@ -579,8 +580,7 @@ abstract class Base
                         $hashObj = new Hash();
                         $hashObj->setHash($hash);
                         if ($dkLen > $hashObj->getLength()) {
-                            user_error('Derived key too long');
-                            return false;
+                            throw new \LengthException('Derived key length cannot be longer than the hash length');
                         }
                         $t = $password . $salt;
                         for ($i = 0; $i < $count; ++$i) {
@@ -1768,6 +1768,7 @@ abstract class Base
      *
      * @see \phpseclib\Crypt\Base::_unpad()
      * @param String $text
+     * @throws \LengthException if padding is disabled and the plaintext's length is not a multiple of the block size
      * @access private
      * @return String
      */
@@ -1779,8 +1780,7 @@ abstract class Base
             if ($length % $this->block_size == 0) {
                 return $text;
             } else {
-                user_error("The plaintext's length ($length) is not a multiple of the block size ({$this->block_size})");
-                $this->padding = true;
+                throw new \LengthException("The plaintext's length ($length) is not a multiple of the block size ({$this->block_size}). Try enabling padding.");
             }
         }
 
@@ -1797,6 +1797,7 @@ abstract class Base
      *
      * @see \phpseclib\Crypt\Base::_pad()
      * @param String $text
+     * @throws \LengthException if the ciphertext's length is not a multiple of the block size
      * @access private
      * @return String
      */
@@ -1809,7 +1810,7 @@ abstract class Base
         $length = ord($text[strlen($text) - 1]);
 
         if (!$length || $length > $this->block_size) {
-            return false;
+            throw new \LengthException("The ciphertext has an invalid padding length ($length) compared to the block size ({$this->block_size})");
         }
 
         return substr($text, 0, -$length);
diff --git a/phpseclib/Crypt/RSA.php b/phpseclib/Crypt/RSA.php
index 78837ddf..9edb9f61 100644
--- a/phpseclib/Crypt/RSA.php
+++ b/phpseclib/Crypt/RSA.php
@@ -2057,14 +2057,14 @@ class RSA
      * @access private
      * @param \phpseclib\Math\BigInteger $x
      * @param Integer $xLen
+     * @throws \OutOfBoundsException if strlen($x) > $xLen
      * @return String
      */
     function _i2osp($x, $xLen)
     {
         $x = $x->toBytes();
         if (strlen($x) > $xLen) {
-            user_error('Integer too large');
-            return false;
+            throw new \OutOfBoundsException('Integer too large');
         }
         return str_pad($x, $xLen, chr(0), STR_PAD_LEFT);
     }
@@ -2219,13 +2219,13 @@ class RSA
      *
      * @access private
      * @param \phpseclib\Math\BigInteger $m
+     * @throws \OutOfRangeException if $m < 0 or $m > $this->modulus
      * @return \phpseclib\Math\BigInteger
      */
     function _rsaep($m)
     {
         if ($m->compare($this->zero) < 0 || $m->compare($this->modulus) > 0) {
-            user_error('Message representative out of range');
-            return false;
+            throw new \OutOfRangeException('Message representative out of range');
         }
         return $this->_exponentiate($m);
     }
@@ -2237,13 +2237,13 @@ class RSA
      *
      * @access private
      * @param \phpseclib\Math\BigInteger $c
+     * @throws \OutOfRangeException if $c < 0 or $c > $this->modulus
      * @return \phpseclib\Math\BigInteger
      */
     function _rsadp($c)
     {
         if ($c->compare($this->zero) < 0 || $c->compare($this->modulus) > 0) {
-            user_error('Ciphertext representative out of range');
-            return false;
+            throw new \OutOfRangeException('Ciphertext representative out of range');
         }
         return $this->_exponentiate($c);
     }
@@ -2255,13 +2255,13 @@ class RSA
      *
      * @access private
      * @param \phpseclib\Math\BigInteger $m
+     * @throws \OutOfRangeException if $m < 0 or $m > $this->modulus
      * @return \phpseclib\Math\BigInteger
      */
     function _rsasp1($m)
     {
         if ($m->compare($this->zero) < 0 || $m->compare($this->modulus) > 0) {
-            user_error('Message representative out of range');
-            return false;
+            throw new \OutOfRangeException('Message representative out of range');
         }
         return $this->_exponentiate($m);
     }
@@ -2273,13 +2273,13 @@ class RSA
      *
      * @access private
      * @param \phpseclib\Math\BigInteger $s
+     * @throws \OutOfRangeException if $s < 0 or $s > $this->modulus
      * @return \phpseclib\Math\BigInteger
      */
     function _rsavp1($s)
     {
         if ($s->compare($this->zero) < 0 || $s->compare($this->modulus) > 0) {
-            user_error('Signature representative out of range');
-            return false;
+            throw new \OutOfRangeException('Signature representative out of range');
         }
         return $this->_exponentiate($s);
     }
@@ -2317,6 +2317,7 @@ class RSA
      * @access private
      * @param String $m
      * @param String $l
+     * @throws \OutOfBoundsException if strlen($m) > $this->k - 2 * $this->hLen - 2
      * @return String
      */
     function _rsaes_oaep_encrypt($m, $l = '')
@@ -2329,8 +2330,7 @@ class RSA
         // be output.
 
         if ($mLen > $this->k - 2 * $this->hLen - 2) {
-            user_error('Message too long');
-            return false;
+            throw new \OutOfBoundsException('Message too long');
         }
 
         // EME-OAEP encoding
@@ -2380,6 +2380,7 @@ class RSA
      * @access private
      * @param String $c
      * @param String $l
+     * @throws \RuntimeException on decryption error
      * @return String
      */
     function _rsaes_oaep_decrypt($c, $l = '')
@@ -2390,8 +2391,7 @@ class RSA
         // be output.
 
         if (strlen($c) != $this->k || $this->k < 2 * $this->hLen + 2) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
 
         // RSA decryption
@@ -2399,8 +2399,7 @@ class RSA
         $c = $this->_os2ip($c);
         $m = $this->_rsadp($c);
         if ($m === false) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
         $em = $this->_i2osp($m, $this->k);
 
@@ -2417,13 +2416,11 @@ class RSA
         $lHash2 = substr($db, 0, $this->hLen);
         $m = substr($db, $this->hLen);
         if ($lHash != $lHash2) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
         $m = ltrim($m, chr(0));
         if (ord($m[0]) != 1) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
 
         // Output the message M
@@ -2454,6 +2451,7 @@ class RSA
      *
      * @access private
      * @param String $m
+     * @throws \OutOfBoundsException if strlen($m) > $this->k - 11
      * @return String
      */
     function _rsaes_pkcs1_v1_5_encrypt($m)
@@ -2463,8 +2461,7 @@ class RSA
         // Length checking
 
         if ($mLen > $this->k - 11) {
-            user_error('Message too long');
-            return false;
+            throw new \OutOfBoundsException('Message too long');
         }
 
         // EME-PKCS1-v1_5 encoding
@@ -2513,6 +2510,7 @@ class RSA
      *
      * @access private
      * @param String $c
+     * @throws \RuntimeException on decryption error
      * @return String
      */
     function _rsaes_pkcs1_v1_5_decrypt($c)
@@ -2520,8 +2518,7 @@ class RSA
         // Length checking
 
         if (strlen($c) != $this->k) { // or if k < 11
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
 
         // RSA decryption
@@ -2530,24 +2527,21 @@ class RSA
         $m = $this->_rsadp($c);
 
         if ($m === false) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
         $em = $this->_i2osp($m, $this->k);
 
         // EME-PKCS1-v1_5 decoding
 
         if (ord($em[0]) != 0 || ord($em[1]) > 2) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
 
         $ps = substr($em, 2, strpos($em, chr(0), 2) - 2);
         $m = substr($em, strlen($ps) + 3);
 
         if (strlen($ps) < 8) {
-            user_error('Decryption error');
-            return false;
+            throw new \RuntimeException('Decryption error');
         }
 
         // Output M
@@ -2562,6 +2556,7 @@ class RSA
      *
      * @access private
      * @param String $m
+     * @throws \RuntimeException on encoding error
      * @param Integer $emBits
      */
     function _emsa_pss_encode($m, $emBits)
@@ -2574,8 +2569,7 @@ class RSA
 
         $mHash = $this->hash->hash($m);
         if ($emLen < $this->hLen + $sLen + 2) {
-            user_error('Encoding error');
-            return false;
+            throw new \RuntimeException('Encoding error');
         }
 
         $salt = Random::string($sLen);
@@ -2672,6 +2666,7 @@ class RSA
      * @access private
      * @param String $m
      * @param String $s
+     * @throws \RuntimeException on invalid signature
      * @return String
      */
     function _rsassa_pss_verify($m, $s)
@@ -2679,8 +2674,7 @@ class RSA
         // Length checking
 
         if (strlen($s) != $this->k) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
 
         // RSA verification
@@ -2690,13 +2684,11 @@ class RSA
         $s2 = $this->_os2ip($s);
         $m2 = $this->_rsavp1($s2);
         if ($m2 === false) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
         $em = $this->_i2osp($m2, $modBits >> 3);
         if ($em === false) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
 
         // EMSA-PSS verification
@@ -2712,6 +2704,7 @@ class RSA
      * @access private
      * @param String $m
      * @param Integer $emLen
+     * @throws \LengthException if the intended encoded message length is too short
      * @return String
      */
     function _emsa_pkcs1_v1_5_encode($m, $emLen)
@@ -2745,8 +2738,7 @@ class RSA
         $tLen = strlen($t);
 
         if ($emLen < $tLen + 11) {
-            user_error('Intended encoded message length too short');
-            return false;
+            throw new \LengthException('Intended encoded message length too short');
         }
 
         $ps = str_repeat(chr(0xFF), $emLen - $tLen - 3);
@@ -2763,6 +2755,7 @@ class RSA
      *
      * @access private
      * @param String $m
+     * @throws \LengthException if the RSA modulus is too short
      * @return String
      */
     function _rsassa_pkcs1_v1_5_sign($m)
@@ -2771,8 +2764,7 @@ class RSA
 
         $em = $this->_emsa_pkcs1_v1_5_encode($m, $this->k);
         if ($em === false) {
-            user_error('RSA modulus too short');
-            return false;
+            throw new \LengthException('RSA modulus too short');
         }
 
         // RSA signature
@@ -2793,6 +2785,8 @@ class RSA
      *
      * @access private
      * @param String $m
+     * @throws \RuntimeException if the signature is invalid
+     * @throws \LengthException if the RSA modulus is too short
      * @return String
      */
     function _rsassa_pkcs1_v1_5_verify($m, $s)
@@ -2800,8 +2794,7 @@ class RSA
         // Length checking
 
         if (strlen($s) != $this->k) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
 
         // RSA verification
@@ -2809,21 +2802,18 @@ class RSA
         $s = $this->_os2ip($s);
         $m2 = $this->_rsavp1($s);
         if ($m2 === false) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
         $em = $this->_i2osp($m2, $this->k);
         if ($em === false) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
 
         // EMSA-PKCS1-v1_5 encoding
 
         $em2 = $this->_emsa_pkcs1_v1_5_encode($m, $this->k);
         if ($em2 === false) {
-            user_error('RSA modulus too short');
-            return false;
+            throw new \LengthException('RSA modulus too short');
         }
 
         // Compare
diff --git a/phpseclib/Crypt/Random.php b/phpseclib/Crypt/Random.php
index 9fb1d15b..e6269035 100644
--- a/phpseclib/Crypt/Random.php
+++ b/phpseclib/Crypt/Random.php
@@ -49,6 +49,7 @@ class Random
      * eg. for RSA key generation.
      *
      * @param Integer $length
+     * @throws \RuntimeException if a symmetric cipher is needed but not loaded
      * @return String
      */
     public static function string($length)
@@ -199,8 +200,7 @@ class Random
                     $crypto = new RC4();
                     break;
                 default:
-                    user_error(__CLASS__ . ' requires at least one symmetric cipher be loaded');
-                    return false;
+                    throw new \RuntimeException(__CLASS__ . ' requires at least one symmetric cipher be loaded');
             }
 
             $crypto->setKey($key);
diff --git a/phpseclib/Exception/BadConfigurationException.php b/phpseclib/Exception/BadConfigurationException.php
new file mode 100644
index 00000000..096148a0
--- /dev/null
+++ b/phpseclib/Exception/BadConfigurationException.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * BadConfigurationException
+ *
+ * PHP version 5
+ *
+ * @category  Exception
+ * @package   BadConfigurationException
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @copyright 2015 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Exception;
+
+/**
+ * BadConfigurationException
+ *
+ * @package BadConfigurationException
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+class BadConfigurationException extends \RuntimeException
+{
+}
diff --git a/phpseclib/Exception/FileNotFoundException.php b/phpseclib/Exception/FileNotFoundException.php
new file mode 100644
index 00000000..984edfcc
--- /dev/null
+++ b/phpseclib/Exception/FileNotFoundException.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * FileNotFoundException
+ *
+ * PHP version 5
+ *
+ * @category  Exception
+ * @package   FileNotFoundException
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @copyright 2015 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Exception;
+
+/**
+ * FileNotFoundException
+ *
+ * @package FileNotFoundException
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+class FileNotFoundException extends \RuntimeException
+{
+}
diff --git a/phpseclib/Exception/NoSupportedAlgorithmsException.php b/phpseclib/Exception/NoSupportedAlgorithmsException.php
new file mode 100644
index 00000000..bca9a753
--- /dev/null
+++ b/phpseclib/Exception/NoSupportedAlgorithmsException.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * NoSupportedAlgorithmsException
+ *
+ * PHP version 5
+ *
+ * @category  Exception
+ * @package   NoSupportedAlgorithmsException
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @copyright 2015 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Exception;
+
+/**
+ * NoSupportedAlgorithmsException
+ *
+ * @package NoSupportedAlgorithmsException
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+class NoSupportedAlgorithmsException extends \RuntimeException
+{
+}
diff --git a/phpseclib/Exception/UnsupportedAlgorithmException.php b/phpseclib/Exception/UnsupportedAlgorithmException.php
new file mode 100644
index 00000000..47cc41d4
--- /dev/null
+++ b/phpseclib/Exception/UnsupportedAlgorithmException.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * UnsupportedAlgorithmException
+ *
+ * PHP version 5
+ *
+ * @category  Exception
+ * @package   UnsupportedAlgorithmException
+ * @author    Jim Wigginton <terrafrost@php.net>
+ * @copyright 2015 Jim Wigginton
+ * @license   http://www.opensource.org/licenses/mit-license.html  MIT License
+ * @link      http://phpseclib.sourceforge.net
+ */
+
+namespace phpseclib\Exception;
+
+/**
+ * UnsupportedAlgorithmException
+ *
+ * @package UnsupportedAlgorithmException
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+class UnsupportedAlgorithmException extends \RuntimeException
+{
+}
diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
index 717f4f8d..fa58ec7f 100644
--- a/phpseclib/File/ASN1.php
+++ b/phpseclib/File/ASN1.php
@@ -793,6 +793,7 @@ class ASN1
      * @param String $mapping
      * @param Integer $idx
      * @return String
+     * @throws \RuntimeException if the input has an error in it
      * @access private
      */
     function _encode_der($source, $mapping, $idx = null, $special = array())
@@ -985,7 +986,7 @@ class ASN1
             case self::TYPE_OBJECT_IDENTIFIER:
                 $oid = preg_match('#(?:\d+\.)+#', $source) ? $source : array_search($source, $this->oids);
                 if ($oid === false) {
-                    user_error('Invalid OID');
+                    throw new \RuntimeException('Invalid OID');
                     return false;
                 }
                 $value = '';
@@ -1038,7 +1039,7 @@ class ASN1
                     $filters = $filters[$part];
                 }
                 if ($filters === false) {
-                    user_error('No filters defined for ' . implode('/', $loc));
+                    throw new \RuntimeException('No filters defined for ' . implode('/', $loc));
                     return false;
                 }
                 return $this->_encode_der($source, $filters + $mapping, null, $special);
@@ -1062,7 +1063,7 @@ class ASN1
                 $value = $source ? "\xFF" : "\x00";
                 break;
             default:
-                user_error('Mapping provides no type definition for ' . implode('/', $this->location));
+                throw new \RuntimeException('Mapping provides no type definition for ' . implode('/', $this->location));
                 return false;
         }
 
diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index cfdfbe2e..cbe16bae 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -32,6 +32,7 @@ use phpseclib\Crypt\Random;
 use phpseclib\File\ASN1;
 use phpseclib\File\ASN1\Element;
 use phpseclib\Math\BigInteger;
+use phpseclib\Exception\UnsupportedAlgorithmException;
 
 /**
  * Pure-PHP X.509 Parser
@@ -1641,7 +1642,7 @@ class X509
                 $map = $this->_getMapping($id);
                 if (is_bool($map)) {
                     if (!$map) {
-                        user_error($id . ' is not a currently supported extension');
+                        //user_error($id . ' is not a currently supported extension');
                         unset($extensions[$i]);
                     }
                 } else {
@@ -1714,7 +1715,7 @@ class X509
                 $id = $attributes[$i]['type'];
                 $map = $this->_getMapping($id);
                 if ($map === false) {
-                    user_error($id . ' is not a currently supported attribute', E_USER_NOTICE);
+                    //user_error($id . ' is not a currently supported attribute', E_USER_NOTICE);
                     unset($attributes[$i]);
                 } elseif (is_array($attributes[$i]['value'])) {
                     $values = &$attributes[$i]['value'];
@@ -2107,7 +2108,8 @@ class X509
     /**
      * Validates a signature
      *
-     * Returns true if the signature is verified, false if it is not correct or null on error
+     * Returns true if the signature is verified and false if it is not correct.
+     * If the algorithms are unsupposed an exception is thrown.
      *
      * @param String $publicKeyAlgorithm
      * @param String $publicKey
@@ -2115,7 +2117,8 @@ class X509
      * @param String $signature
      * @param String $signatureSubject
      * @access private
-     * @return Integer
+     * @throws \phpseclib\Exception\UnsupportedAlgorithmException if the algorithm is unsupported
+     * @return Boolean
      */
     function _validateSignature($publicKeyAlgorithm, $publicKey, $signatureAlgorithm, $signature, $signatureSubject)
     {
@@ -2139,11 +2142,11 @@ class X509
                         }
                         break;
                     default:
-                        return null;
+                        throw new UnsupportedAlgorithmException('Signature algorithm unsupported');
                 }
                 break;
             default:
-                return null;
+                throw new UnsupportedAlgorithmException('Public key algorithm unsupported');
         }
 
         return true;
@@ -3628,6 +3631,7 @@ class X509
      * @param \phpseclib\File\X509 $subject
      * @param String $signatureAlgorithm
      * @access public
+     * @throws \phpseclib\Exception\UnsupportedAlgorithmException if the algorithm is unsupported
      * @return Mixed
      */
     function _sign($key, $signatureAlgorithm)
@@ -3646,10 +3650,12 @@ class X509
 
                     $this->currentCert['signature'] = base64_encode("\0" . $key->sign($this->signatureSubject));
                     return $this->currentCert;
+                default:
+                    throw new UnsupportedAlgorithmException('Signature algorithm unsupported');
             }
         }
 
-        return false;
+        throw new UnsupportedAlgorithmException('Unsupported public key algorithm');
     }
 
     /**
diff --git a/phpseclib/Net/SCP.php b/phpseclib/Net/SCP.php
index 678297e0..ebfa999a 100644
--- a/phpseclib/Net/SCP.php
+++ b/phpseclib/Net/SCP.php
@@ -34,6 +34,7 @@ namespace phpseclib\Net;
 
 use phpseclib\Net\SSH1;
 use phpseclib\Net\SSH2;
+use phpseclib\Exception\FileNotFoundException;
 
 /**
  * Pure-PHP implementations of SCP.
@@ -140,6 +141,7 @@ class SCP
      * @param String $data
      * @param optional Integer $mode
      * @param optional Callable $callback
+     * @throws \phpseclib\Exception\FileNotFoundException if you're uploading via a file and the file doesn't exist
      * @return Boolean
      * @access public
      */
@@ -168,8 +170,7 @@ class SCP
             $size = strlen($data);
         } else {
             if (!is_file($data)) {
-                user_error("$data is not a valid file", E_USER_NOTICE);
-                return false;
+                throw new FileNotFoundException("$data is not a valid file");
             }
 
             $fp = @fopen($data, 'rb');
@@ -289,6 +290,7 @@ class SCP
      * Receives a packet from an SSH server
      *
      * @return String
+     * @throws \UnexpectedValueException on receipt of an unexpected packet
      * @access private
      */
     function _receive()
@@ -314,8 +316,7 @@ class SCP
                             $this->ssh->bitmap = 0;
                             return false;
                         default:
-                            user_error('Unknown packet received', E_USER_NOTICE);
-                            return false;
+                            throw new \UnexpectedValueException('Unknown packet received');
                     }
                 }
         }
diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index 60d8923d..8460a1c9 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -38,6 +38,7 @@
 namespace phpseclib\Net;
 
 use phpseclib\Net\SSH2;
+use phpseclib\Exception\FileNotFoundException;
 
 /**
  * Pure-PHP implementations of SFTP.
@@ -383,6 +384,7 @@ class SFTP extends SSH2
      *
      * @param String $username
      * @param optional String $password
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Boolean
      * @access public
      */
@@ -470,8 +472,7 @@ class SFTP extends SSH2
 
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_VERSION) {
-            user_error('Expected SSH_FXP_VERSION');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_VERSION');
         }
 
         extract(unpack('Nversion', $this->_string_shift($response, 4)));
@@ -610,6 +611,7 @@ class SFTP extends SSH2
      *
      * @see \phpseclib\Net\SFTP::chdir()
      * @param String $path
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Mixed
      * @access private
      */
@@ -634,8 +636,7 @@ class SFTP extends SSH2
                     $this->_logError($response);
                     return false;
                 default:
-                    user_error('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
-                    return false;
+                    throw new \UnexpectedValueException('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
             }
         }
 
@@ -666,6 +667,7 @@ class SFTP extends SSH2
      * Changes the current directory
      *
      * @param String $dir
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Boolean
      * @access public
      */
@@ -710,8 +712,7 @@ class SFTP extends SSH2
                 $this->_logError($response);
                 return false;
             default:
-                user_error('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
         }
 
         if (!$this->_close_handle($handle)) {
@@ -813,6 +814,7 @@ class SFTP extends SSH2
      * @param String $dir
      * @param optional Boolean $raw
      * @return Mixed
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @access private
      */
     function _list($dir, $raw = true)
@@ -844,8 +846,7 @@ class SFTP extends SSH2
                 $this->_logError($response);
                 return false;
             default:
-                user_error('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
         }
 
         $this->_update_stat_cache($dir, array());
@@ -899,8 +900,7 @@ class SFTP extends SSH2
                     }
                     break 2;
                 default:
-                    user_error('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
-                    return false;
+                    throw new \UnexpectedValueException('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
             }
         }
 
@@ -1259,6 +1259,7 @@ class SFTP extends SSH2
      *
      * @param String $filename
      * @param Integer $type
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Mixed
      * @access private
      */
@@ -1279,8 +1280,7 @@ class SFTP extends SSH2
                 return false;
         }
 
-        user_error('Expected SSH_FXP_ATTRS or SSH_FXP_STATUS');
-        return false;
+        throw new \UnexpectedValueException('Expected SSH_FXP_ATTRS or SSH_FXP_STATUS');
     }
 
     /**
@@ -1306,6 +1306,7 @@ class SFTP extends SSH2
      * @param String $filename
      * @param optional Integer $time
      * @param optional Integer $atime
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Boolean
      * @access public
      */
@@ -1342,8 +1343,7 @@ class SFTP extends SSH2
                 $this->_logError($response);
                 break;
             default:
-                user_error('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
         }
 
         return $this->_setstat($filename, $attr, false);
@@ -1396,6 +1396,7 @@ class SFTP extends SSH2
      * @param Integer $mode
      * @param String $filename
      * @param optional Boolean $recursive
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Mixed
      * @access public
      */
@@ -1433,8 +1434,7 @@ class SFTP extends SSH2
                 return false;
         }
 
-        user_error('Expected SSH_FXP_ATTRS or SSH_FXP_STATUS');
-        return false;
+        throw new \UnexpectedValueException('Expected SSH_FXP_ATTRS or SSH_FXP_STATUS');
     }
 
     /**
@@ -1443,6 +1443,7 @@ class SFTP extends SSH2
      * @param String $filename
      * @param String $attr
      * @param Boolean $recursive
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Boolean
      * @access private
      */
@@ -1481,8 +1482,7 @@ class SFTP extends SSH2
         */
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         extract(unpack('Nstatus', $this->_string_shift($response, 4)));
@@ -1570,6 +1570,7 @@ class SFTP extends SSH2
      * Return the target of a symbolic link
      *
      * @param String $link
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Mixed
      * @access public
      */
@@ -1593,8 +1594,7 @@ class SFTP extends SSH2
                 $this->_logError($response);
                 return false;
             default:
-                user_error('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_NAME or SSH_FXP_STATUS');
         }
 
         extract(unpack('Ncount', $this->_string_shift($response, 4)));
@@ -1614,6 +1614,7 @@ class SFTP extends SSH2
      *
      * @param String $target
      * @param String $link
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Boolean
      * @access public
      */
@@ -1633,8 +1634,7 @@ class SFTP extends SSH2
 
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         extract(unpack('Nstatus', $this->_string_shift($response, 4)));
@@ -1686,6 +1686,7 @@ class SFTP extends SSH2
      *
      * @param String $dir
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @access private
      */
     function _mkdir_helper($dir, $attr)
@@ -1696,8 +1697,7 @@ class SFTP extends SSH2
 
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         extract(unpack('Nstatus', $this->_string_shift($response, 4)));
@@ -1713,6 +1713,7 @@ class SFTP extends SSH2
      * Removes a directory.
      *
      * @param String $dir
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Boolean
      * @access public
      */
@@ -1733,8 +1734,7 @@ class SFTP extends SSH2
 
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         extract(unpack('Nstatus', $this->_string_shift($response, 4)));
@@ -1794,6 +1794,9 @@ class SFTP extends SSH2
      * @param optional Integer $start
      * @param optional Integer $local_start
      * @param optional callable|null $progressCallback
+     * @throws \UnexpectedValueException on receipt of unexpected packets
+     * @throws \BadFunctionCallException if you're uploading via a callback and the callback function is invalid
+     * @throws \phpseclib\Exception\FileNotFoundException if you're uploading via a file and the file doesn't exist
      * @return Boolean
      * @access public
      * @internal ASCII mode for SFTPv4/5/6 can be supported by adding a new function - \phpseclib\Net\SFTP::setMode().
@@ -1841,8 +1844,7 @@ class SFTP extends SSH2
                 $this->_logError($response);
                 return false;
             default:
-                user_error('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
         }
 
         // http://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-8.2.3
@@ -1850,7 +1852,7 @@ class SFTP extends SSH2
         switch (true) {
             case $mode & self::SOURCE_CALLBACK:
                 if (!is_callable($data)) {
-                    user_error("\$data should be is_callable() if you specify SOURCE_CALLBACK flag");
+                    throw new \BadFunctionCallException("\$data should be is_callable() if you specify SOURCE_CALLBACK flag");
                 }
                 $dataCallback = $data;
                 // do nothing
@@ -1861,8 +1863,7 @@ class SFTP extends SSH2
                 break;
             case $mode & self::SOURCE_LOCAL_FILE:
                 if (!is_file($data)) {
-                    user_error("$data is not a valid file");
-                    return false;
+                    throw new FileNotFoundException("$data is not a valid file");
                 }
                 $fp = @fopen($data, 'rb');
                 if (!$fp) {
@@ -1950,6 +1951,7 @@ class SFTP extends SSH2
      *
      * @param Integer $i
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @access private
      */
     function _read_put_responses($i)
@@ -1957,8 +1959,7 @@ class SFTP extends SSH2
         while ($i--) {
             $response = $this->_get_sftp_packet();
             if ($this->packet_type != NET_SFTP_STATUS) {
-                user_error('Expected SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
             }
 
             extract(unpack('Nstatus', $this->_string_shift($response, 4)));
@@ -1976,6 +1977,7 @@ class SFTP extends SSH2
      *
      * @param String $handle
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @access private
      */
     function _close_handle($handle)
@@ -1988,8 +1990,7 @@ class SFTP extends SSH2
         //  -- http://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-8.1.3
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         extract(unpack('Nstatus', $this->_string_shift($response, 4)));
@@ -2014,6 +2015,7 @@ class SFTP extends SSH2
      * @param optional String $local_file
      * @param optional Integer $offset
      * @param optional Integer $length
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @return Mixed
      * @access public
      */
@@ -2042,8 +2044,7 @@ class SFTP extends SSH2
                 $this->_logError($response);
                 return false;
             default:
-                user_error('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_FXP_HANDLE or SSH_FXP_STATUS');
         }
 
         if (is_resource($local_file)) {
@@ -2091,11 +2092,10 @@ class SFTP extends SSH2
                     $this->_logError($response);
                     break 2;
                 default:
-                    user_error('Expected SSH_FXP_DATA or SSH_FXP_STATUS');
                     if ($fclose_check) {
                         fclose($fp);
                     }
-                    return false;
+                    throw new \UnexpectedValueException('Expected SSH_FXP_DATA or SSH_FXP_STATUS');
             }
 
             if ($length > 0 && $length <= $offset - $start) {
@@ -2129,6 +2129,7 @@ class SFTP extends SSH2
      * @param String $path
      * @param Boolean $recursive
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @access public
      */
     function delete($path, $recursive = true)
@@ -2149,8 +2150,7 @@ class SFTP extends SSH2
 
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         // if $status isn't SSH_FX_OK it's probably SSH_FX_NO_SUCH_FILE or SSH_FX_PERMISSION_DENIED
@@ -2482,6 +2482,7 @@ class SFTP extends SSH2
      * @param String $oldname
      * @param String $newname
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
      * @access public
      */
     function rename($oldname, $newname)
@@ -2504,8 +2505,7 @@ class SFTP extends SSH2
 
         $response = $this->_get_sftp_packet();
         if ($this->packet_type != NET_SFTP_STATUS) {
-            user_error('Expected SSH_FXP_STATUS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_FXP_STATUS');
         }
 
         // if $status isn't SSH_FX_OK it's probably SSH_FX_NO_SUCH_FILE or SSH_FX_PERMISSION_DENIED
diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index 210af478..0daf81dc 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -60,6 +60,7 @@ use phpseclib\Crypt\TripleDES;
 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;
 
 /**
  * Pure-PHP implementation of SSHv2.
@@ -989,6 +990,8 @@ class SSH2
      * Connect to an SSHv2 server
      *
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
+     * @throws \RuntimeException on other errors
      * @access private
      */
     function _connect()
@@ -1008,8 +1011,7 @@ class SSH2
             $this->fsock = @fsockopen($this->host, $this->port, $errno, $errstr, $this->curTimeout);
             if (!$this->fsock) {
                 $host = $this->host . ':' . $this->port;
-                user_error(rtrim("Cannot connect to $host. Error $errno. $errstr"));
-                return false;
+                throw new \RuntimeException(rtrim("Cannot connect to $host. Error $errno. $errstr"));
             }
             $elapsed = microtime(true) - $start;
 
@@ -1060,8 +1062,7 @@ class SSH2
         }
 
         if (feof($this->fsock)) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         $this->identifier = $this->_generate_identifier();
@@ -1077,21 +1078,18 @@ class SSH2
         }
 
         if ($matches[1] != '1.99' && $matches[1] != '2.0') {
-            user_error("Cannot connect to SSH $matches[1] servers");
-            return false;
+            throw new \RuntimeException("Cannot connect to SSH $matches[1] servers");
         }
 
         fputs($this->fsock, $this->identifier . "\r\n");
 
         $response = $this->_get_binary_packet();
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         if (ord($response[0]) != NET_SSH2_MSG_KEXINIT) {
-            user_error('Expected SSH_MSG_KEXINIT');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_MSG_KEXINIT');
         }
 
         if (!$this->_key_exchange($response)) {
@@ -1143,6 +1141,9 @@ class SSH2
      * Key Exchange
      *
      * @param String $kexinit_payload_server
+     * @throws \UnexpectedValueException on receipt of unexpected packets
+     * @throws \RuntimeException on other errors
+     * @throws \phpseclib\Exception\NoSupportedAlgorithmsException when none of the algorithms phpseclib has loaded are compatible
      * @access private
      */
     function _key_exchange($kexinit_payload_server)
@@ -1354,27 +1355,28 @@ class SSH2
         // here ends the second place.
 
         // we need to decide upon the symmetric encryption algorithms before we do the diffie-hellman key exchange
+
         // we don't initialize any crypto-objects, yet - we do that, later. for now, we need the lengths to make the
         // diffie-hellman key exchange as fast as possible
         $decrypt = $this->_array_intersect_first($encryption_algorithms, $this->encryption_algorithms_server_to_client);
         $decryptKeyLength = $this->_encryption_algorithm_to_key_size($decrypt);
         if ($decryptKeyLength === null) {
-            user_error('No compatible server to client encryption algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible server to client encryption algorithms found');
         }
 
         $encrypt = $this->_array_intersect_first($encryption_algorithms, $this->encryption_algorithms_client_to_server);
         $encryptKeyLength = $this->_encryption_algorithm_to_key_size($encrypt);
         if ($encryptKeyLength === null) {
-            user_error('No compatible client to server encryption algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible client to server encryption algorithms found');
         }
 
         // through diffie-hellman key exchange a symmetric key is obtained
         $kex_algorithm = $this->_array_intersect_first($kex_algorithms, $this->kex_algorithms);
         if ($kex_algorithm === false) {
-            user_error('No compatible key exchange algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible key exchange algorithms found');
         }
 
         // Only relevant in diffie-hellman-group-exchange-sha{1,256}, otherwise empty.
@@ -1491,20 +1493,17 @@ class SSH2
         $data = pack('CNa*', $clientKexInitMessage, strlen($eBytes), $eBytes);
 
         if (!$this->_send_binary_packet($data)) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         $response = $this->_get_binary_packet();
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
         extract(unpack('Ctype', $this->_string_shift($response, 1)));
 
         if ($type != $serverKexReplyMessage) {
-            user_error('Expected SSH_MSG_KEXDH_REPLY');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_MSG_KEXDH_REPLY');
         }
 
         $temp = unpack('Nlength', $this->_string_shift($response, 4));
@@ -1564,13 +1563,13 @@ class SSH2
 
         $server_host_key_algorithm = $this->_array_intersect_first($server_host_key_algorithms, $this->server_host_key_algorithms);
         if ($server_host_key_algorithm === false) {
-            user_error('No compatible server host key algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible server host key algorithms found');
         }
 
         if ($public_key_format != $server_host_key_algorithm || $this->signature_format != $server_host_key_algorithm) {
-            user_error('Server Host Key Algorithm Mismatch');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new \RuntimeException('Server Host Key Algorithm Mismatch');
         }
 
         $packet = pack(
@@ -1585,15 +1584,13 @@ class SSH2
         $response = $this->_get_binary_packet();
 
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         extract(unpack('Ctype', $this->_string_shift($response, 1)));
 
         if ($type != NET_SSH2_MSG_NEWKEYS) {
-            user_error('Expected SSH_MSG_NEWKEYS');
-            return false;
+            throw new \UnexpectedValueException('Expected SSH_MSG_NEWKEYS');
         }
 
         $keyBytes = pack('Na*', strlen($keyBytes), $keyBytes);
@@ -1662,8 +1659,8 @@ class SSH2
 
         $mac_algorithm = $this->_array_intersect_first($mac_algorithms, $this->mac_algorithms_client_to_server);
         if ($mac_algorithm === false) {
-            user_error('No compatible client to server message authentication algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible client to server message authentication algorithms found');
         }
 
         $createKeyLength = 0; // ie. $mac_algorithm == 'none'
@@ -1691,8 +1688,8 @@ class SSH2
 
         $mac_algorithm = $this->_array_intersect_first($mac_algorithms, $this->mac_algorithms_server_to_client);
         if ($mac_algorithm === false) {
-            user_error('No compatible server to client message authentication algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible server to client message authentication algorithms found');
         }
 
         $checkKeyLength = 0;
@@ -1738,15 +1735,15 @@ class SSH2
 
         $compression_algorithm = $this->_array_intersect_first($compression_algorithms, $this->compression_algorithms_server_to_client);
         if ($compression_algorithm === false) {
-            user_error('No compatible server to client compression algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible server to client compression algorithms found');
         }
         $this->decompress = $compression_algorithm == 'zlib';
 
         $compression_algorithm = $this->_array_intersect_first($compression_algorithms, $this->compression_algorithms_client_to_server);
         if ($compression_algorithm === false) {
-            user_error('No compatible client to server compression algorithms found');
-            return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+            throw new NoSupportedAlgorithmsException('No compatible client to server compression algorithms found');
         }
         $this->compress = $compression_algorithm == 'zlib';
 
@@ -1891,6 +1888,8 @@ class SSH2
      * @param String $username
      * @param optional String $password
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
+     * @throws \RuntimeException on other errors
      * @access private
      * @internal It might be worthwhile, at some point, to protect against {@link http://tools.ietf.org/html/rfc4251#section-9.3.9 traffic analysis}
      *           by sending dummy SSH_MSG_IGNORE messages.
@@ -1915,15 +1914,13 @@ class SSH2
 
             $response = $this->_get_binary_packet();
             if ($response === false) {
-                user_error('Connection closed by server');
-                return false;
+                throw new \RuntimeException('Connection closed by server');
             }
 
             extract(unpack('Ctype', $this->_string_shift($response, 1)));
 
             if ($type != NET_SSH2_MSG_SERVICE_ACCEPT) {
-                user_error('Expected SSH_MSG_SERVICE_ACCEPT');
-                return false;
+                throw new \UnexpectedValueException('Expected SSH_MSG_SERVICE_ACCEPT');
             }
             $this->bitmap |= self::MASK_LOGIN_REQ;
         }
@@ -1964,8 +1961,7 @@ class SSH2
 
             $response = $this->_get_binary_packet();
             if ($response === false) {
-                user_error('Connection closed by server');
-                return false;
+                throw new \RuntimeException('Connection closed by server');
             }
 
             extract(unpack('Ctype', $this->_string_shift($response, 1)));
@@ -2019,8 +2015,7 @@ class SSH2
 
         $response = $this->_get_binary_packet();
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         extract(unpack('Ctype', $this->_string_shift($response, 1)));
@@ -2096,6 +2091,7 @@ class SSH2
      *
      * @param String $responses...
      * @return Boolean
+     * @throws \RuntimeException on connection error
      * @access private
      */
     function _keyboard_interactive_process()
@@ -2107,8 +2103,7 @@ class SSH2
         } else {
             $orig = $response = $this->_get_binary_packet();
             if ($response === false) {
-                user_error('Connection closed by server');
-                return false;
+                throw new \RuntimeException('Connection closed by server');
             }
         }
 
@@ -2232,6 +2227,7 @@ class SSH2
      * @param String $username
      * @param \phpseclib\Crypt\RSA $password
      * @return Boolean
+     * @throws \RuntimeException on connection error
      * @access private
      * @internal It might be worthwhile, at some point, to protect against {@link http://tools.ietf.org/html/rfc4251#section-9.3.9 traffic analysis}
      *           by sending dummy SSH_MSG_IGNORE messages.
@@ -2277,8 +2273,7 @@ class SSH2
 
         $response = $this->_get_binary_packet();
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         extract(unpack('Ctype', $this->_string_shift($response, 1)));
@@ -2312,8 +2307,7 @@ class SSH2
 
         $response = $this->_get_binary_packet();
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         extract(unpack('Ctype', $this->_string_shift($response, 1)));
@@ -2363,6 +2357,7 @@ class SSH2
      * @param String $command
      * @param optional Callback $callback
      * @return String
+     * @throws \RuntimeException on connection error
      * @access public
      */
     function exec($command, $callback = null)
@@ -2430,8 +2425,7 @@ class SSH2
 
             $response = $this->_get_binary_packet();
             if ($response === false) {
-                user_error('Connection closed by server');
-                return false;
+                throw new \RuntimeException('Connection closed by server');
             }
 
             list(, $type) = unpack('C', $this->_string_shift($response, 1));
@@ -2441,8 +2435,8 @@ class SSH2
                     break;
                 case NET_SSH2_MSG_CHANNEL_FAILURE:
                 default:
-                    user_error('Unable to request pseudo-terminal');
-                    return $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                    $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                    throw new \RuntimeException('Unable to request pseudo-terminal');
             }
             $this->in_request_pty_exec = true;
         }
@@ -2510,6 +2504,8 @@ class SSH2
      * @see \phpseclib\Net\SSH2::read()
      * @see \phpseclib\Net\SSH2::write()
      * @return Boolean
+     * @throws \UnexpectedValueException on receipt of unexpected packets
+     * @throws \RuntimeException on other errors
      * @access private
      */
     function _initShell()
@@ -2566,8 +2562,7 @@ class SSH2
 
         $response = $this->_get_binary_packet();
         if ($response === false) {
-            user_error('Connection closed by server');
-            return false;
+            throw new \RuntimeException('Connection closed by server');
         }
 
         list(, $type) = unpack('C', $this->_string_shift($response, 1));
@@ -2578,8 +2573,8 @@ class SSH2
             case NET_SSH2_MSG_CHANNEL_FAILURE:
                 break;
             default:
-                user_error('Unable to request pseudo-terminal');
-                return $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                throw new \UnexpectedValueException('Unable to request pseudo-terminal');
         }
 
         $packet = pack(
@@ -2656,6 +2651,7 @@ class SSH2
      * @param String $expect
      * @param Integer $mode
      * @return String
+     * @throws \RuntimeException on connection error
      * @access public
      */
     function read($expect = '', $mode = self::READ_SIMPLE)
@@ -2664,13 +2660,11 @@ class SSH2
         $this->is_timeout = false;
 
         if (!($this->bitmap & self::MASK_LOGIN)) {
-            user_error('Operation disallowed prior to login()');
-            return false;
+            throw new \RuntimeException('Operation disallowed prior to login()');
         }
 
         if (!($this->bitmap & self::MASK_SHELL) && !$this->_initShell()) {
-            user_error('Unable to initiate an interactive shell session');
-            return false;
+            throw new \RuntimeException('Unable to initiate an interactive shell session');
         }
 
         $channel = $this->_get_interactive_channel();
@@ -2701,18 +2695,17 @@ class SSH2
      * @see \phpseclib\Net\SSH2::read()
      * @param String $cmd
      * @return Boolean
+     * @throws \RuntimeException on connection error
      * @access public
      */
     function write($cmd)
     {
         if (!($this->bitmap & self::MASK_LOGIN)) {
-            user_error('Operation disallowed prior to login()');
-            return false;
+            throw new \RuntimeException('Operation disallowed prior to login()');
         }
 
         if (!($this->bitmap & self::MASK_SHELL) && !$this->_initShell()) {
-            user_error('Unable to initiate an interactive shell session');
-            return false;
+            throw new \RuntimeException('Unable to initiate an interactive shell session');
         }
 
         return $this->_send_channel_packet($this->_get_interactive_channel(), $cmd);
@@ -2869,14 +2862,14 @@ class SSH2
      *
      * @see \phpseclib\Net\SSH2::_send_binary_packet()
      * @return String
+     * @throws \RuntimeException on connection errors
      * @access private
      */
     function _get_binary_packet()
     {
         if (!is_resource($this->fsock) || feof($this->fsock)) {
-            user_error('Connection closed prematurely');
             $this->bitmap = 0;
-            return false;
+            throw new \RuntimeException('Connection closed prematurely');
         }
 
         $start = microtime(true);
@@ -2890,8 +2883,7 @@ class SSH2
             $raw = $this->decrypt->decrypt($raw);
         }
         if ($raw === false) {
-            user_error('Unable to decrypt content');
-            return false;
+            throw new \RuntimeException('Unable to decrypt content');
         }
 
         extract(unpack('Npacket_length/Cpadding_length', $this->_string_shift($raw, 5)));
@@ -2902,17 +2894,15 @@ class SSH2
         // "implementations SHOULD check that the packet length is reasonable"
         // PuTTY uses 0x9000 as the actual max packet size and so to shall we
         if ($remaining_length < -$this->decrypt_block_size || $remaining_length > 0x9000 || $remaining_length % $this->decrypt_block_size != 0) {
-            user_error('Invalid size');
-            return false;
+            throw new \RuntimeException('Invalid size');
         }
 
         $buffer = '';
         while ($remaining_length > 0) {
             $temp = fread($this->fsock, $remaining_length);
             if ($temp === false || feof($this->fsock)) {
-                user_error('Error reading from socket');
                 $this->bitmap = 0;
-                return false;
+                throw new \RuntimeException('Error reading from socket');
             }
             $buffer.= $temp;
             $remaining_length-= strlen($temp);
@@ -2928,12 +2918,10 @@ class SSH2
         if ($this->hmac_check !== false) {
             $hmac = fread($this->fsock, $this->hmac_size);
             if ($hmac === false || strlen($hmac) != $this->hmac_size) {
-                user_error('Error reading socket');
                 $this->bitmap = 0;
-                return false;
+                throw new \RuntimeException('Error reading socket');
             } elseif ($hmac != $this->hmac_check->hash(pack('NNCa*', $this->get_seq_no, $packet_length, $padding_length, $payload . $padding))) {
-                user_error('Invalid HMAC');
-                return false;
+                throw new \RuntimeException('Invalid HMAC');
             }
         }
 
@@ -3161,6 +3149,7 @@ class SSH2
      *
      * @param $client_channel
      * @return Mixed
+     * @throws \RuntimeException on connection error
      * @access private
      */
     function _get_channel_packet($client_channel, $skip_extended = false)
@@ -3193,8 +3182,7 @@ class SSH2
 
             $response = $this->_get_binary_packet();
             if ($response === false) {
-                user_error('Connection closed by server');
-                return false;
+                throw new \RuntimeException('Connection closed by server');
             }
             if ($client_channel == -1 && $response === true) {
                 return true;
@@ -3243,8 +3231,8 @@ class SSH2
                                 return $result;
                             //case NET_SSH2_MSG_CHANNEL_OPEN_FAILURE:
                             default:
-                                user_error('Unable to open channel');
-                                return $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                                $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                                throw new \RuntimeException('Unable to open channel');
                         }
                         break;
                     case NET_SSH2_MSG_CHANNEL_REQUEST:
@@ -3254,8 +3242,8 @@ class SSH2
                             case NET_SSH2_MSG_CHANNEL_FAILURE:
                                 return false;
                             default:
-                                user_error('Unable to fulfill channel request');
-                                return $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                                $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                                throw new \RuntimeException('Unable to fulfill channel request');
                         }
                     case NET_SSH2_MSG_CHANNEL_CLOSE:
                         return $type == NET_SSH2_MSG_CHANNEL_CLOSE ? true : $this->_get_channel_packet($client_channel, $skip_extended);
@@ -3364,8 +3352,8 @@ class SSH2
                 case NET_SSH2_MSG_CHANNEL_EOF:
                     break;
                 default:
-                    user_error('Error reading channel data');
-                    return $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                    $this->_disconnect(NET_SSH2_DISCONNECT_BY_APPLICATION);
+                    throw new \RuntimeException('Error reading channel data');
             }
         }
     }
@@ -3384,9 +3372,8 @@ class SSH2
     function _send_binary_packet($data, $logged = null)
     {
         if (!is_resource($this->fsock) || feof($this->fsock)) {
-            user_error('Connection closed prematurely');
             $this->bitmap = 0;
-            return false;
+            throw new \RuntimeException('Connection closed prematurely');
         }
 
         //if ($this->compress) {
@@ -3945,6 +3932,8 @@ class SSH2
      * is recommended.  Returns false if the server signature is not signed correctly with the public host key.
      *
      * @return Mixed
+     * @throws \RuntimeException on badly formatted keys
+     * @throws \phpseclib\Exception\NoSupportedAlgorithmsException when the key isn't in a supported format
      * @access public
      */
     function getServerPublicHostKey()
@@ -3990,8 +3979,8 @@ class SSH2
                    padding, unsigned, and in network byte order). */
                 $temp = unpack('Nlength', $this->_string_shift($signature, 4));
                 if ($temp['length'] != 40) {
-                    user_error('Invalid signature');
-                    return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+                    $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+                    throw new \RuntimeException('Invalid signature');
                 }
 
                 $r = new BigInteger($this->_string_shift($signature, 20), 256);
@@ -4002,8 +3991,8 @@ class SSH2
                     case $r->compare($q) >= 0:
                     case $s->equals($zero):
                     case $s->compare($q) >= 0:
-                        user_error('Invalid signature');
-                        return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+                        $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+                        throw new \RuntimeException('Invalid signature');
                 }
 
                 $w = $s->modInverse($q);
@@ -4022,7 +4011,7 @@ class SSH2
                 list(, $v) = $v->divide($q);
 
                 if (!$v->equals($r)) {
-                    user_error('Bad server signature');
+                    //user_error('Bad server signature');
                     return $this->_disconnect(NET_SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE);
                 }
 
@@ -4044,7 +4033,7 @@ class SSH2
                 $rsa->setSignatureMode(RSA::SIGNATURE_PKCS1);
                 $rsa->loadKey(array('e' => $e, 'n' => $n), RSA::PUBLIC_FORMAT_RAW);
                 if (!$rsa->verify($this->exchange_hash, $signature)) {
-                    user_error('Bad server signature');
+                    //user_error('Bad server signature');
                     return $this->_disconnect(NET_SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE);
                 }
                 */
@@ -4059,8 +4048,8 @@ class SSH2
                 // also, see SSHRSA.c (rsa2_verifysig) in PuTTy's source.
 
                 if ($s->compare(new BigInteger()) < 0 || $s->compare($n->subtract(new BigInteger(1))) > 0) {
-                    user_error('Invalid signature');
-                    return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+                    $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
+                    throw new \RuntimeException('Invalid signature');
                 }
 
                 $s = $s->modPow($e, $n);
@@ -4070,13 +4059,13 @@ class SSH2
                 $h = chr(0x01) . str_repeat(chr(0xFF), $nLength - 2 - strlen($h)) . $h;
 
                 if ($s != $h) {
-                    user_error('Bad server signature');
+                    //user_error('Bad server signature');
                     return $this->_disconnect(NET_SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE);
                 }
                 break;
             default:
-                user_error('Unsupported signature format');
-                return $this->_disconnect(NET_SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE);
+                $this->_disconnect(NET_SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE);
+                throw new NoSupportedAlgorithmsException('Unsupported signature format');
         }
 
         return $this->signature_format . ' ' . base64_encode($this->server_public_host_key);
diff --git a/phpseclib/System/SSH/Agent.php b/phpseclib/System/SSH/Agent.php
index 4cb9dec0..5ec47169 100644
--- a/phpseclib/System/SSH/Agent.php
+++ b/phpseclib/System/SSH/Agent.php
@@ -35,6 +35,7 @@ namespace phpseclib\System\SSH;
 
 use phpseclib\Crypt\RSA;
 use phpseclib\System\SSH\Agent\Identity;
+use phpseclib\Exception\BadConfigurationException;
 
 /**
  * Pure-PHP ssh-agent client identity factory
@@ -115,6 +116,8 @@ class Agent
      * Default Constructor
      *
      * @return \phpseclib\System\SSH\Agent
+     * @throws \phpseclib\Exception\BadConfigurationException if SSH_AUTH_SOCK cannot be found
+     * @throws \RuntimeException on connection errors
      * @access public
      */
     function __construct()
@@ -127,13 +130,12 @@ class Agent
                 $address = $_ENV['SSH_AUTH_SOCK'];
                 break;
             default:
-                user_error('SSH_AUTH_SOCK not found');
-                return false;
+                throw new \BadConfigurationException('SSH_AUTH_SOCK not found');
         }
 
         $this->fsock = fsockopen('unix://' . $address, 0, $errno, $errstr);
         if (!$this->fsock) {
-            user_error("Unable to connect to ssh-agent (Error $errno: $errstr)");
+            throw new \RuntimeException("Unable to connect to ssh-agent (Error $errno: $errstr)");
         }
     }
 
@@ -144,6 +146,7 @@ class Agent
      * Returns an array containing zero or more \phpseclib\System\SSH\Agent\Identity objects
      *
      * @return Array
+     * @throws \RuntimeException on receipt of unexpected packets
      * @access public
      */
     function requestIdentities()
@@ -154,13 +157,13 @@ class Agent
 
         $packet = pack('NC', 1, self::SSH_AGENTC_REQUEST_IDENTITIES);
         if (strlen($packet) != fputs($this->fsock, $packet)) {
-            user_error('Connection closed while requesting identities');
+            throw new \RuntimeException('Connection closed while requesting identities');
         }
 
         $length = current(unpack('N', fread($this->fsock, 4)));
         $type = ord(fread($this->fsock, 1));
         if ($type != self::SSH_AGENT_IDENTITIES_ANSWER) {
-            user_error('Unable to request identities');
+            throw new \RuntimeException('Unable to request identities');
         }
 
         $identities = array();
@@ -271,6 +274,7 @@ class Agent
      *
      * @param String $data
      * @return data from SSH Agent
+     * @throws \RuntimeException on connection errors
      * @access private
      */
     function _forward_data($data)
@@ -289,7 +293,7 @@ class Agent
         }
 
         if (strlen($this->socket_buffer) != fwrite($this->fsock, $this->socket_buffer)) {
-            user_error('Connection closed attempting to forward data to SSH agent');
+            throw new \RuntimeException('Connection closed attempting to forward data to SSH agent');
         }
 
         $this->socket_buffer = '';
diff --git a/phpseclib/System/SSH/Agent/Identity.php b/phpseclib/System/SSH/Agent/Identity.php
index 490edf6e..82fd224c 100644
--- a/phpseclib/System/SSH/Agent/Identity.php
+++ b/phpseclib/System/SSH/Agent/Identity.php
@@ -134,6 +134,7 @@ class Identity
      *
      * @param String $message
      * @return String
+     * @throws \RuntimeException on connection errors
      * @access public
      */
     function sign($message)
@@ -142,13 +143,13 @@ class Identity
         $packet = pack('CNa*Na*N', Agent::SSH_AGENTC_SIGN_REQUEST, strlen($this->key_blob), $this->key_blob, strlen($message), $message, 0);
         $packet = pack('Na*', strlen($packet), $packet);
         if (strlen($packet) != fputs($this->fsock, $packet)) {
-            user_error('Connection closed during signing');
+            throw new \RuntimeException('Connection closed during signing');
         }
 
         $length = current(unpack('N', fread($this->fsock, 4)));
         $type = ord(fread($this->fsock, 1));
         if ($type != Agent::SSH_AGENT_SIGN_RESPONSE) {
-            user_error('Unable to retreive signature');
+            throw new \RuntimeException('Unable to retreive signature');
         }
 
         $signature_blob = fread($this->fsock, $length - 1);