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+<?php
+/**
+ * A class to handle secure encryption and decryption of arbitrary data
+ * Copyright http://stackoverflow.com/users/338665/ircmaxell
+ * http://stackoverflow.com/questions/5089841/php-2-way-encryption-i-need-to-store-passwords-that-can-be-retrieved
+ *
+ *
+ * Note that this is not just straight encryption. It also has a few other
+ * features in it to make the encrypted data far more secure. Note that any
+ * other implementations used to decrypt data will have to do the same exact
+ * operations.
+ *
+ * Security Benefits:
+ *
+ * - Uses Key stretching
+ * - Hides the Initialization Vector
+ * - Does HMAC verification of source data
+ *
+ */
+class Encryption {
+
+ /**
+ * @var string $cipher The mcrypt cipher to use for this instance
+ */
+ protected $cipher = '';
+
+ /**
+ * @var int $mode The mcrypt cipher mode to use
+ */
+ protected $mode = '';
+
+ /**
+ * @var int $rounds The number of rounds to feed into PBKDF2 for key generation
+ */
+ protected $rounds = 100;
+
+ /**
+ * Constructor!
+ *
+ * @param string $cipher The MCRYPT_* cypher to use for this instance
+ * @param int $mode The MCRYPT_MODE_* mode to use for this instance
+ * @param int $rounds The number of PBKDF2 rounds to do on the key
+ */
+ public function __construct($cipher, $mode, $rounds = 100) {
+ $this->cipher = $cipher;
+ $this->mode = $mode;
+ $this->rounds = (int) $rounds;
+ }
+
+ /**
+ * Decrypt the data with the provided key
+ *
+ * @param string $data The encrypted datat to decrypt
+ * @param string $key The key to use for decryption
+ *
+ * @returns string|false The returned string if decryption is successful
+ * false if it is not
+ */
+ public function decrypt($data, $key) {
+ $salt = substr($data, 0, 128);
+ $enc = substr($data, 128, -64);
+ $mac = substr($data, -64);
+
+ list ($cipherKey, $macKey, $iv) = $this->getKeys($salt, $key);
+
+ if ($mac !== hash_hmac('sha512', $enc, $macKey, true)) {
+ return false;
+ }
+
+ $dec = mcrypt_decrypt($this->cipher, $cipherKey, $enc, $this->mode, $iv);
+
+ $data = $this->unpad($dec);
+
+ return $data;
+ }
+
+ /**
+ * Encrypt the supplied data using the supplied key
+ *
+ * @param string $data The data to encrypt
+ * @param string $key The key to encrypt with
+ *
+ * @returns string The encrypted data
+ */
+ public function encrypt($data, $key) {
+ $salt = mcrypt_create_iv(128, MCRYPT_DEV_URANDOM);
+ list ($cipherKey, $macKey, $iv) = $this->getKeys($salt, $key);
+
+ $data = $this->pad($data);
+
+ $enc = mcrypt_encrypt($this->cipher, $cipherKey, $data, $this->mode, $iv);
+
+ $mac = hash_hmac('sha512', $enc, $macKey, true);
+ return $salt . $enc . $mac;
+ }
+
+ /**
+ * Generates a set of keys given a random salt and a master key
+ *
+ * @param string $salt A random string to change the keys each encryption
+ * @param string $key The supplied key to encrypt with
+ *
+ * @returns array An array of keys (a cipher key, a mac key, and a IV)
+ */
+ protected function getKeys($salt, $key) {
+ $ivSize = mcrypt_get_iv_size($this->cipher, $this->mode);
+ $keySize = mcrypt_get_key_size($this->cipher, $this->mode);
+ $length = 2 * $keySize + $ivSize;
+
+ $key = $this->pbkdf2('sha512', $key, $salt, $this->rounds, $length);
+
+ $cipherKey = substr($key, 0, $keySize);
+ $macKey = substr($key, $keySize, $keySize);
+ $iv = substr($key, 2 * $keySize);
+ return array($cipherKey, $macKey, $iv);
+ }
+
+ /**
+ * Stretch the key using the PBKDF2 algorithm
+ *
+ * @see http://en.wikipedia.org/wiki/PBKDF2
+ *
+ * @param string $algo The algorithm to use
+ * @param string $key The key to stretch
+ * @param string $salt A random salt
+ * @param int $rounds The number of rounds to derive
+ * @param int $length The length of the output key
+ *
+ * @returns string The derived key.
+ */
+ protected function pbkdf2($algo, $key, $salt, $rounds, $length) {
+ $size = strlen(hash($algo, '', true));
+ $len = ceil($length / $size);
+ $result = '';
+ for ($i = 1; $i <= $len; $i++) {
+ $tmp = hash_hmac($algo, $salt . pack('N', $i), $key, true);
+ $res = $tmp;
+ for ($j = 1; $j < $rounds; $j++) {
+ $tmp = hash_hmac($algo, $tmp, $key, true);
+ $res ^= $tmp;
+ }
+ $result .= $res;
+ }
+ return substr($result, 0, $length);
+ }
+
+ protected function pad($data) {
+ $length = mcrypt_get_block_size($this->cipher, $this->mode);
+ $padAmount = $length - strlen($data) % $length;
+ if ($padAmount == 0) {
+ $padAmount = $length;
+ }
+ return $data . str_repeat(chr($padAmount), $padAmount);
+ }
+
+ protected function unpad($data) {
+ $length = mcrypt_get_block_size($this->cipher, $this->mode);
+ $last = ord($data[strlen($data) - 1]);
+ if ($last > $length) return false;
+ if (substr($data, -1 * $last) !== str_repeat(chr($last), $last)) {
+ return false;
+ }
+ return substr($data, 0, -1 * $last);
+ }
+}
+?>

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