diff --git a/phpseclib/Crypt/RSA.php b/phpseclib/Crypt/RSA.php
index 36609d90..d36c5f74 100644
--- a/phpseclib/Crypt/RSA.php
+++ b/phpseclib/Crypt/RSA.php
@@ -432,7 +432,7 @@ class Crypt_RSA {
     /**
      * OpenSSL configuration file name.
      *
-     * Set to NULL to use system configuration file.
+     * Set to null to use system configuration file.
      * @see Crypt_RSA::createKey()
      * @var Mixed
      * @Access public
@@ -554,7 +554,7 @@ class Crypt_RSA {
                 $config['config'] = $this->configFile;
             }
             $rsa = openssl_pkey_new(array('private_key_bits' => $bits) + $config);
-            openssl_pkey_export($rsa, $privatekey, NULL, $config);
+            openssl_pkey_export($rsa, $privatekey, null, $config);
             $publickey = openssl_pkey_get_details($rsa);
             $publickey = $publickey['key'];
 
diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
index bee3fab8..37199d26 100644
--- a/phpseclib/File/ASN1.php
+++ b/phpseclib/File/ASN1.php
@@ -544,13 +544,13 @@ class File_ASN1 {
                         return array($key => $value);
                     }
                 }
-                return NULL;
+                return null;
             case isset($mapping['implicit']):
             case isset($mapping['explicit']):
             case $decoded['type'] == $mapping['type']:
                 break;
             default:
-                return NULL;
+                return null;
         }
 
         if (isset($mapping['implicit'])) {
@@ -565,8 +565,8 @@ class File_ASN1 {
                 if (isset($mapping['min']) && isset($mapping['max'])) {
                     $child = $mapping['children'];
                     foreach ($decoded['content'] as $content) {
-                        if (($map[] = $this->asn1map($content, $child, $special)) === NULL) {
-                            return NULL;
+                        if (($map[] = $this->asn1map($content, $child, $special)) === null) {
+                            return null;
                         }
                     }
 
@@ -584,7 +584,7 @@ class File_ASN1 {
                         if ($child['type'] != FILE_ASN1_TYPE_CHOICE) {
                             // Get the mapping and input class & constant.
                             $childClass = $tempClass = FILE_ASN1_CLASS_UNIVERSAL;
-                            $constant = NULL;
+                            $constant = null;
                             if (isset($temp['constant'])) {
                                 $tempClass = isset($temp['class']) ? $temp['class'] : FILE_ASN1_CLASS_CONTEXT_SPECIFIC;
                             }
@@ -610,7 +610,7 @@ class File_ASN1 {
                     if ($maymatch) {
                         // Attempt submapping.
                         $candidate = $this->asn1map($temp, $child, $special);
-                        $maymatch = $candidate !== NULL;
+                        $maymatch = $candidate !== null;
                     }
 
                     if ($maymatch) {
@@ -623,12 +623,12 @@ class File_ASN1 {
                     } elseif (isset($child['default'])) {
                         $map[$key] = $child['default']; // Use default.
                     } elseif (!isset($child['optional'])) {
-                        return NULL; // Syntax error.
+                        return null; // Syntax error.
                     }
                 }
 
                 // Fail mapping if all input items have not been consumed.
-                return $i < $n? NULL: $map;
+                return $i < $n? null: $map;
 
             // the main diff between sets and sequences is the encapsulation of the foreach in another for loop
             case FILE_ASN1_TYPE_SET:
@@ -638,8 +638,8 @@ class File_ASN1 {
                 if (isset($mapping['min']) && isset($mapping['max'])) {
                     $child = $mapping['children'];
                     foreach ($decoded['content'] as $content) {
-                        if (($map[] = $this->asn1map($content, $child, $special)) === NULL) {
-                            return NULL;
+                        if (($map[] = $this->asn1map($content, $child, $special)) === null) {
+                            return null;
                         }
                     }
 
@@ -660,7 +660,7 @@ class File_ASN1 {
                         $maymatch = true;
                         if ($child['type'] != FILE_ASN1_TYPE_CHOICE) {
                             $childClass = FILE_ASN1_CLASS_UNIVERSAL;
-                            $constant = NULL;
+                            $constant = null;
                             if (isset($child['class'])) {
                                 $childClass = $child['class'];
                                 $constant = $child['cast'];
@@ -682,7 +682,7 @@ class File_ASN1 {
                         if ($maymatch) {
                             // Attempt submapping.
                             $candidate = $this->asn1map($temp, $child, $special);
-                            $maymatch = $candidate !== NULL;
+                            $maymatch = $candidate !== null;
                         }
 
                         if (!$maymatch) {
@@ -703,7 +703,7 @@ class File_ASN1 {
                         if (isset($child['default'])) {
                             $map[$key] = $child['default'];
                         } elseif (!isset($child['optional'])) {
-                            return NULL;
+                            return null;
                         }
                     }
                 }
@@ -796,7 +796,7 @@ class File_ASN1 {
     function encodeDER($source, $mapping, $special = array())
     {
         $this->location = array();
-        return $this->_encode_der($source, $mapping, NULL, $special);
+        return $this->_encode_der($source, $mapping, null, $special);
     }
 
     /**
@@ -818,7 +818,7 @@ class File_ASN1 {
      * @return String
      * @access private
      */
-    function _encode_der($source, $mapping, $idx = NULL, $special = array())
+    function _encode_der($source, $mapping, $idx = null, $special = array())
     {
         if (is_object($source) && strtolower(get_class($source)) == 'file_asn1_element') {
             return $source->element;
@@ -849,7 +849,7 @@ class File_ASN1 {
                     $child = $mapping['children'];
 
                     foreach ($source as $content) {
-                        $temp = $this->_encode_der($content, $child, NULL, $special);
+                        $temp = $this->_encode_der($content, $child, null, $special);
                         if ($temp === false) {
                             return false;
                         }
@@ -1029,19 +1029,19 @@ class File_ASN1 {
 
                 switch (true) {
                     case !isset($source):
-                        return $this->_encode_der(NULL, array('type' => FILE_ASN1_TYPE_NULL) + $mapping, NULL, $special);
+                        return $this->_encode_der(null, array('type' => FILE_ASN1_TYPE_NULL) + $mapping, null, $special);
                     case is_int($source):
                     case is_object($source) && strtolower(get_class($source)) == 'math_biginteger':
-                        return $this->_encode_der($source, array('type' => FILE_ASN1_TYPE_INTEGER) + $mapping, NULL, $special);
+                        return $this->_encode_der($source, array('type' => FILE_ASN1_TYPE_INTEGER) + $mapping, null, $special);
                     case is_float($source):
-                        return $this->_encode_der($source, array('type' => FILE_ASN1_TYPE_REAL) + $mapping, NULL, $special);
+                        return $this->_encode_der($source, array('type' => FILE_ASN1_TYPE_REAL) + $mapping, null, $special);
                     case is_bool($source):
-                        return $this->_encode_der($source, array('type' => FILE_ASN1_TYPE_BOOLEAN) + $mapping, NULL, $special);
+                        return $this->_encode_der($source, array('type' => FILE_ASN1_TYPE_BOOLEAN) + $mapping, null, $special);
                     case is_array($source) && count($source) == 1:
                         $typename = implode('', array_keys($source));
                         $outtype = array_search($typename, $this->ANYmap, true);
                         if ($outtype !== false) {
-                            return $this->_encode_der($source[$typename], array('type' => $outtype) + $mapping, NULL, $special);
+                            return $this->_encode_der($source[$typename], array('type' => $outtype) + $mapping, null, $special);
                         }
                     }
 
@@ -1057,7 +1057,7 @@ class File_ASN1 {
                     user_error('No filters defined for ' . implode('/', $loc));
                     return false;
                 }
-                return $this->_encode_der($source, $filters + $mapping, NULL, $special);
+                return $this->_encode_der($source, $filters + $mapping, null, $special);
             case FILE_ASN1_TYPE_NULL:
                 $value = '';
                 break;
diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index 963308eb..3408165e 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -1430,7 +1430,7 @@ class File_X509 {
             $this->currentCert = $cert;
 
             $currentKeyIdentifier = $this->getExtension('id-ce-subjectKeyIdentifier');
-            $this->currentKeyIdentifier = is_string($currentKeyIdentifier) ? $currentKeyIdentifier : NULL;
+            $this->currentKeyIdentifier = is_string($currentKeyIdentifier) ? $currentKeyIdentifier : null;
 
             unset($this->signatureSubject);
 
@@ -1468,7 +1468,7 @@ class File_X509 {
         $this->dn = $x509['tbsCertificate']['subject'];
 
         $currentKeyIdentifier = $this->getExtension('id-ce-subjectKeyIdentifier');
-        $this->currentKeyIdentifier = is_string($currentKeyIdentifier) ? $currentKeyIdentifier : NULL;
+        $this->currentKeyIdentifier = is_string($currentKeyIdentifier) ? $currentKeyIdentifier : null;
 
         return $x509;
     }
@@ -1962,7 +1962,7 @@ class File_X509 {
      * @param Integer $date optional
      * @access public
      */
-    function validateDate($date = NULL)
+    function validateDate($date = null)
     {
         if (!is_array($this->currentCert) || !isset($this->currentCert['tbsCertificate'])) {
             return false;
@@ -1991,7 +1991,7 @@ class File_X509 {
      * Validate a signature
      *
      * Works on X.509 certs, CSR's and CRL's.
-     * Returns true if the signature is verified, false if it is not correct or NULL on error
+     * Returns true if the signature is verified, false if it is not correct or null on error
      *
      * By default returns false for self-signed certs. Call validateSignature(false) to make this support
      * self-signed.
@@ -2005,7 +2005,7 @@ class File_X509 {
     function validateSignature($caonly = true)
     {
         if (!is_array($this->currentCert) || !isset($this->signatureSubject)) {
-            return NULL;
+            return null;
         }
 
         /* TODO:
@@ -2106,7 +2106,7 @@ class File_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, false if it is not correct or null on error
      *
      * @param String $publicKeyAlgorithm
      * @param String $publicKey
@@ -2141,11 +2141,11 @@ class File_X509 {
                         }
                         break;
                     default:
-                        return NULL;
+                        return null;
                 }
                 break;
             default:
-                return NULL;
+                return null;
         }
 
         return true;
@@ -2366,7 +2366,7 @@ class File_X509 {
      * @return Mixed
      * @access public
      */
-    function getDNProp($propName, $dn = NULL, $withType = false)
+    function getDNProp($propName, $dn = null, $withType = false)
     {
         if (!isset($dn)) {
             $dn = $this->dn;
@@ -2420,7 +2420,7 @@ class File_X509 {
     function setDN($dn, $merge = false, $type = 'utf8String')
     {
         if (!$merge) {
-            $this->dn = NULL;
+            $this->dn = null;
         }
 
         if (is_array($dn)) {
@@ -2459,7 +2459,7 @@ class File_X509 {
      * @access public
      * @return Boolean
      */
-    function getDN($format = FILE_X509_DN_ARRAY, $dn = NULL)
+    function getDN($format = FILE_X509_DN_ARRAY, $dn = null)
     {
         if (!isset($dn)) {
             $dn = isset($this->currentCert['tbsCertList']) ? $this->currentCert['tbsCertList']['issuer'] : $this->dn;
@@ -2675,7 +2675,7 @@ class File_X509 {
     {
         switch (true) {
             case !empty($this->dn):
-                return $this->getDNProp($propName, NULL, $withType);
+                return $this->getDNProp($propName, null, $withType);
             case !isset($this->currentCert) || !is_array($this->currentCert):
                 break;
             case isset($this->currentCert['tbsCertificate']):
@@ -2871,10 +2871,10 @@ class File_X509 {
                 $this->publicKey->setPublicKey();
                 break;
             default:
-                $this->publicKey = NULL;
+                $this->publicKey = null;
         }
 
-        $this->currentKeyIdentifier = NULL;
+        $this->currentKeyIdentifier = null;
         $this->currentCert = $csr;
 
         return $csr;
@@ -2996,10 +2996,10 @@ class File_X509 {
                 $this->publicKey->setPublicKey();
                 break;
             default:
-                $this->publicKey = NULL;
+                $this->publicKey = null;
         }
 
-        $this->currentKeyIdentifier = NULL;
+        $this->currentKeyIdentifier = null;
         $this->currentCert = $spkac;
 
         return $spkac;
@@ -3054,7 +3054,7 @@ class File_X509 {
             }
         }
 
-        $this->currentKeyIdentifier = NULL;
+        $this->currentKeyIdentifier = null;
         $this->currentCert = $crl;
 
         return $crl;
@@ -3138,8 +3138,8 @@ class File_X509 {
             return false;
         }
 
-        $currentCert = isset($this->currentCert) ? $this->currentCert : NULL;
-        $signatureSubject = isset($this->signatureSubject) ? $this->signatureSubject: NULL;
+        $currentCert = isset($this->currentCert) ? $this->currentCert : null;
+        $signatureSubject = isset($this->signatureSubject) ? $this->signatureSubject: null;
 
         if (isset($subject->currentCert) && is_array($subject->currentCert) && isset($subject->currentCert['tbsCertificate'])) {
             $this->currentCert = $subject->currentCert;
@@ -3311,8 +3311,8 @@ class File_X509 {
         }
         $this->publicKey = $origPublicKey;
 
-        $currentCert = isset($this->currentCert) ? $this->currentCert : NULL;
-        $signatureSubject = isset($this->signatureSubject) ? $this->signatureSubject: NULL;
+        $currentCert = isset($this->currentCert) ? $this->currentCert : null;
+        $signatureSubject = isset($this->signatureSubject) ? $this->signatureSubject: null;
 
         if (isset($this->currentCert) && is_array($this->currentCert) && isset($this->currentCert['certificationRequestInfo'])) {
             $this->currentCert['signatureAlgorithm']['algorithm'] =
@@ -3365,8 +3365,8 @@ class File_X509 {
             return false;
         }
 
-        $currentCert = isset($this->currentCert) ? $this->currentCert : NULL;
-        $signatureSubject = isset($this->signatureSubject) ? $this->signatureSubject : NULL;
+        $currentCert = isset($this->currentCert) ? $this->currentCert : null;
+        $signatureSubject = isset($this->signatureSubject) ? $this->signatureSubject : null;
         $thisUpdate = !empty($this->startDate) ? $this->startDate : @date('D, d M y H:i:s O');
 
         if (isset($crl->currentCert) && is_array($crl->currentCert) && isset($crl->currentCert['tbsCertList'])) {
@@ -3402,7 +3402,7 @@ class File_X509 {
         }
         else {
             $crlNumber = $this->getExtension('id-ce-cRLNumber');
-            $crlNumber = $crlNumber !== false ? $crlNumber->add(new Math_BigInteger(1)) : NULL;
+            $crlNumber = $crlNumber !== false ? $crlNumber->add(new Math_BigInteger(1)) : null;
         }
 
         $this->removeExtension('id-ce-authorityKeyIdentifier');
@@ -3612,7 +3612,7 @@ class File_X509 {
      * @access private
      * @return array ref or false
      */
-    function &_extensions(&$root, $path = NULL, $create = false)
+    function &_extensions(&$root, $path = null, $create = false)
     {
         if (!isset($root)) {
             $root = $this->currentCert;
@@ -3666,7 +3666,7 @@ class File_X509 {
      * @access private
      * @return Boolean
      */
-    function _removeExtension($id, $path = NULL)
+    function _removeExtension($id, $path = null)
     {
         $extensions = &$this->_extensions($this->currentCert, $path);
 
@@ -3697,7 +3697,7 @@ class File_X509 {
      * @access private
      * @return Mixed
      */
-    function _getExtension($id, $cert = NULL, $path = NULL)
+    function _getExtension($id, $cert = null, $path = null)
     {
         $extensions = $this->_extensions($cert, $path);
 
@@ -3722,7 +3722,7 @@ class File_X509 {
      * @access private
      * @return Array
      */
-    function _getExtensions($cert = NULL, $path = NULL)
+    function _getExtensions($cert = null, $path = null)
     {
         $exts = $this->_extensions($cert, $path);
         $extensions = array();
@@ -3747,7 +3747,7 @@ class File_X509 {
      * @access private
      * @return Boolean
      */
-    function _setExtension($id, $value, $critical = false, $replace = true, $path = NULL)
+    function _setExtension($id, $value, $critical = false, $replace = true, $path = null)
     {
         $extensions = &$this->_extensions($this->currentCert, $path, true);
 
@@ -3794,7 +3794,7 @@ class File_X509 {
      * @access public
      * @return Mixed
      */
-    function getExtension($id, $cert = NULL)
+    function getExtension($id, $cert = null)
     {
         return $this->_getExtension($id, $cert);
     }
@@ -3806,7 +3806,7 @@ class File_X509 {
      * @access public
      * @return Array
      */
-    function getExtensions($cert = NULL)
+    function getExtensions($cert = null)
     {
         return $this->_getExtensions($cert);
     }
@@ -3885,7 +3885,7 @@ class File_X509 {
      * @access public
      * @return Mixed
      */
-    function getAttribute($id, $disposition = FILE_X509_ATTR_ALL, $csr = NULL)
+    function getAttribute($id, $disposition = FILE_X509_ATTR_ALL, $csr = null)
     {
         if (empty($csr)) {
             $csr = $this->currentCert;
@@ -3925,7 +3925,7 @@ class File_X509 {
      * @access public
      * @return Array
      */
-    function getAttributes($csr = NULL)
+    function getAttributes($csr = null)
     {
         if (empty($csr)) {
             $csr = $this->currentCert;
@@ -4034,7 +4034,7 @@ class File_X509 {
      * @access public
      * @return String binary key identifier
      */
-    function computeKeyIdentifier($key = NULL, $method = 1)
+    function computeKeyIdentifier($key = null, $method = 1)
     {
         if (is_null($key)) {
             $key = $this;
@@ -4227,7 +4227,7 @@ class File_X509 {
      * @access public
      * @return Boolean
      */
-    function revoke($serial, $date = NULL)
+    function revoke($serial, $date = null)
     {
         if (isset($this->currentCert['tbsCertList'])) {
             if (is_array($rclist = &$this->_subArray($this->currentCert, 'tbsCertList/revokedCertificates', true))) {
@@ -4292,7 +4292,7 @@ class File_X509 {
      * @access public
      * @return array
      */
-    function listRevoked($crl = NULL)
+    function listRevoked($crl = null)
     {
         if (!isset($crl)) {
             $crl = $this->currentCert;
@@ -4343,7 +4343,7 @@ class File_X509 {
      * @access public
      * @return Mixed
      */
-    function getRevokedCertificateExtension($serial, $id, $crl = NULL)
+    function getRevokedCertificateExtension($serial, $id, $crl = null)
     {
         if (!isset($crl)) {
             $crl = $this->currentCert;
@@ -4366,7 +4366,7 @@ class File_X509 {
      * @access public
      * @return Array
      */
-    function getRevokedCertificateExtensions($serial, $crl = NULL)
+    function getRevokedCertificateExtensions($serial, $crl = null)
     {
         if (!isset($crl)) {
             $crl = $this->currentCert;
diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index f5eb4056..a73850c5 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -1057,7 +1057,7 @@ class Net_SFTP extends Net_SSH2 {
      * @return Boolean
      * @access public
      */
-    function touch($filename, $time = NULL, $atime = NULL)
+    function touch($filename, $time = null, $atime = null)
     {
         if (!($this->bitmap & NET_SSH2_MASK_LOGIN)) {
             return false;
@@ -1100,7 +1100,7 @@ class Net_SFTP extends Net_SSH2 {
     /**
      * Changes file or directory owner
      *
-     * Returns TRUE on success or FALSE on error.
+     * Returns true on success or false on error.
      *
      * @param String $filename
      * @param Integer $uid
@@ -1120,7 +1120,7 @@ class Net_SFTP extends Net_SSH2 {
     /**
      * Changes file or directory group
      *
-     * Returns TRUE on success or FALSE on error.
+     * Returns true on success or false on error.
      *
      * @param String $filename
      * @param Integer $gid
@@ -1138,8 +1138,8 @@ class Net_SFTP extends Net_SSH2 {
     /**
      * Set permissions on a file.
      *
-     * Returns the new file permissions on success or FALSE on error.
-     * If $recursive is true than this just returns TRUE or FALSE.
+     * Returns the new file permissions on success or false on error.
+     * If $recursive is true than this just returns true or false.
      *
      * @param Integer $mode
      * @param String $filename
diff --git a/phpseclib/Net/SSH1.php b/phpseclib/Net/SSH1.php
index a64d06d4..46f4dba9 100644
--- a/phpseclib/Net/SSH1.php
+++ b/phpseclib/Net/SSH1.php
@@ -1016,7 +1016,7 @@ class Net_SSH1 {
 
         if ($this->curTimeout) {
             $read = array($this->fsock);
-            $write = $except = NULL;
+            $write = $except = null;
 
             $start = strtok(microtime(), ' ') + strtok(''); // http://php.net/microtime#61838
             $sec = floor($this->curTimeout);
diff --git a/phpseclib/Net/SSH2.php b/phpseclib/Net/SSH2.php
index e8f1c935..e9d11319 100644
--- a/phpseclib/Net/SSH2.php
+++ b/phpseclib/Net/SSH2.php
@@ -860,7 +860,7 @@ class Net_SSH2 {
         }
 
         $read = array($this->fsock);
-        $write = $except = NULL;
+        $write = $except = null;
 
         $sec = floor($timeout);
         $usec = 1000000 * ($timeout - $sec);
@@ -1756,7 +1756,7 @@ class Net_SSH2 {
 
         // remove the username and password from the logged packet
         if (!defined('NET_SSH2_LOGGING')) {
-            $logged = NULL;
+            $logged = null;
         } else {
             $logged = pack('CNa*Na*Na*CNa*',
                 NET_SSH2_MSG_USERAUTH_REQUEST, strlen('username'), 'username', strlen('ssh-connection'), 'ssh-connection',
@@ -2074,7 +2074,7 @@ class Net_SSH2 {
      * @return String
      * @access public
      */
-    function exec($command, $callback = NULL)
+    function exec($command, $callback = null)
     {
         $this->curTimeout = $this->timeout;
         $this->is_timeout = false;
@@ -2721,7 +2721,7 @@ class Net_SSH2 {
                 }
 
                 $read = array($this->fsock);
-                $write = $except = NULL;
+                $write = $except = null;
 
                 $start = strtok(microtime(), ' ') + strtok(''); // http://php.net/microtime#61838
                 $sec = floor($this->curTimeout);
@@ -2904,7 +2904,7 @@ class Net_SSH2 {
      * @return Boolean
      * @access private
      */
-    function _send_binary_packet($data, $logged = NULL)
+    function _send_binary_packet($data, $logged = null)
     {
         if (!is_resource($this->fsock) || feof($this->fsock)) {
             user_error('Connection closed prematurely');
diff --git a/tests/code_sniffer_ruleset.xml b/tests/code_sniffer_ruleset.xml
index 58e32dd7..3a7633a2 100644
--- a/tests/code_sniffer_ruleset.xml
+++ b/tests/code_sniffer_ruleset.xml
@@ -11,7 +11,6 @@
  <rule ref="Generic.ControlStructures.InlineControlStructure.Discouraged"><severity>0</severity></rule>
  <rule ref="Generic.Files.LineLength.TooLong"><severity>0</severity></rule>
  <rule ref="Generic.Functions.FunctionCallArgumentSpacing.NoSpaceAfterComma"><severity>0</severity></rule>
- <rule ref="Generic.PHP.LowerCaseConstant.Found"><severity>0</severity></rule>
  <rule ref="PEAR.NamingConventions.ValidFunctionName.FunctionNoCapital"><severity>0</severity></rule>
  <rule ref="PEAR.NamingConventions.ValidFunctionName.NotCamelCaps"><severity>0</severity></rule>
  <rule ref="PEAR.Classes.ClassDeclaration.OpenBraceNewLine"><severity>0</severity></rule>