diff --git a/phpseclib/Crypt/RSA.php b/phpseclib/Crypt/RSA.php
index 049ef222..34f65fe7 100644
--- a/phpseclib/Crypt/RSA.php
+++ b/phpseclib/Crypt/RSA.php
@@ -2010,14 +2010,14 @@ 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);
     }
@@ -2172,13 +2172,13 @@ 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);
     }
@@ -2190,13 +2190,13 @@ 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);
     }
@@ -2208,13 +2208,13 @@ 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);
     }
@@ -2226,13 +2226,13 @@ 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);
     }
@@ -2270,6 +2270,7 @@ 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 = '')
@@ -2282,8 +2283,7 @@ 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
@@ -2333,6 +2333,7 @@ class RSA
      * @access private
      * @param String $c
      * @param String $l
+     * @throws \RuntimeException on decryption error
      * @return String
      */
     function _rsaes_oaep_decrypt($c, $l = '')
@@ -2343,8 +2344,7 @@ 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
@@ -2352,8 +2352,7 @@ 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);
 
@@ -2370,13 +2369,11 @@ 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
@@ -2407,6 +2404,7 @@ class RSA
      *
      * @access private
      * @param String $m
+     * @throws \OutOfBoundsException if strlen($m) > $this->k - 11
      * @return String
      */
     function _rsaes_pkcs1_v1_5_encrypt($m)
@@ -2416,8 +2414,7 @@ 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
@@ -2466,6 +2463,7 @@ class RSA
      *
      * @access private
      * @param String $c
+     * @throws \RuntimeException on decryption error
      * @return String
      */
     function _rsaes_pkcs1_v1_5_decrypt($c)
@@ -2473,8 +2471,7 @@ 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
@@ -2483,24 +2480,21 @@ 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
@@ -2515,6 +2509,7 @@ class RSA
      *
      * @access private
      * @param String $m
+     * @throws \RuntimeException on encoding error
      * @param Integer $emBits
      */
     function _emsa_pss_encode($m, $emBits)
@@ -2527,8 +2522,7 @@ 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);
@@ -2625,6 +2619,7 @@ class RSA
      * @access private
      * @param String $m
      * @param String $s
+     * @throws \RuntimeException on invalid signature
      * @return String
      */
     function _rsassa_pss_verify($m, $s)
@@ -2632,8 +2627,7 @@ class RSA
         // Length checking
 
         if (strlen($s) != $this->k) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeException('Invalid signature');
         }
 
         // RSA verification
@@ -2643,13 +2637,11 @@ 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
@@ -2665,6 +2657,7 @@ 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)
@@ -2698,8 +2691,7 @@ 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);
@@ -2716,6 +2708,7 @@ 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)
@@ -2724,8 +2717,7 @@ 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
@@ -2746,6 +2738,8 @@ 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)
@@ -2753,8 +2747,7 @@ class RSA
         // Length checking
 
         if (strlen($s) != $this->k) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeSignature('Invalid signature');
         }
 
         // RSA verification
@@ -2762,21 +2755,18 @@ class RSA
         $s = $this->_os2ip($s);
         $m2 = $this->_rsavp1($s);
         if ($m2 === false) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeSignature('Invalid signature');
         }
         $em = $this->_i2osp($m2, $this->k);
         if ($em === false) {
-            user_error('Invalid signature');
-            return false;
+            throw new \RuntimeSignature('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/Exception/DecryptionException.php b/phpseclib/Exception/DecryptionException.php
new file mode 100644
index 00000000..edc7963d
--- /dev/null
+++ b/phpseclib/Exception/DecryptionException.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * DecryptionException
+ *
+ * PHP version 5
+ *
+ * @category  Exception
+ * @package   DecryptionException
+ * @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;
+
+/**
+ * KeyGenerationException
+ *
+ * @package DecryptionException
+ * @author  Jim Wigginton <terrafrost@php.net>
+ */
+class DecryptionException extends \Exception
+{
+}