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<?php
/**
* @link http://www.yiiframework.com/
* @copyright Copyright (c) 2008 Yii Software LLC
* @license http://www.yiiframework.com/license/
*/
namespace yii\base;
use yii\helpers\StringHelper;
use Yii;
/**
* Security provides a set of methods to handle common security-related tasks.
*
* In particular, Security supports the following features:
*
* - Encryption/decryption: [[encryptByKey()]], [[decryptByKey()]], [[encryptByPassword()]] and [[decryptByPassword()]]
* - Key derivation using standard algorithms: [[pbkdf2()]] and [[hkdf()]]
* - Data tampering prevention: [[hashData()]] and [[validateData()]]
* - Password validation: [[generatePasswordHash()]] and [[validatePassword()]]
*
* > Note: this class requires 'OpenSSL' PHP extension for random key/string generation on Windows and
* for encryption/decryption on all platforms. For the highest security level PHP version >= 5.5.0 is recommended.
*
* For more details and usage information on Security, see the [guide article on security](guide:security-overview).
*
* @author Qiang Xue <qiang.xue@gmail.com>
* @author Tom Worster <fsb@thefsb.org>
* @author Klimov Paul <klimov.paul@gmail.com>
* @since 2.0
*/
class Security extends Component
{
/**
* @var string The cipher to use for encryption and decryption.
*/
public $cipher = 'AES-128-CBC';
/**
* @var array[] Look-up table of block sizes and key sizes for each supported OpenSSL cipher.
*
* In each element, the key is one of the ciphers supported by OpenSSL (@see openssl_get_cipher_methods()).
* The value is an array of two integers, the first is the cipher's block size in bytes and the second is
* the key size in bytes.
*
* > Warning: All OpenSSL ciphers that we recommend are in the default value, i.e. AES in CBC mode.
*
* > Note: Yii's encryption protocol uses the same size for cipher key, HMAC signature key and key
* derivation salt.
*/
public $allowedCiphers = [
'AES-128-CBC' => [16, 16],
'AES-192-CBC' => [16, 24],
'AES-256-CBC' => [16, 32],
];
/**
* @var string Hash algorithm for key derivation. Recommend sha256, sha384 or sha512.
* @see [hash_algos()](http://php.net/manual/en/function.hash-algos.php)
*/
public $kdfHash = 'sha256';
/**
* @var string Hash algorithm for message authentication. Recommend sha256, sha384 or sha512.
* @see [hash_algos()](http://php.net/manual/en/function.hash-algos.php)
*/
public $macHash = 'sha256';
/**
* @var string HKDF info value for derivation of message authentication key.
* @see hkdf()
*/
public $authKeyInfo = 'AuthorizationKey';
/**
* @var int derivation iterations count.
* Set as high as possible to hinder dictionary password attacks.
*/
public $derivationIterations = 100000;
/**
* @var string strategy, which should be used to generate password hash.
* Available strategies:
* - 'password_hash' - use of PHP `password_hash()` function with PASSWORD_DEFAULT algorithm.
* This option is recommended, but it requires PHP version >= 5.5.0
* - 'crypt' - use PHP `crypt()` function.
* @deprecated since version 2.0.7, [[generatePasswordHash()]] ignores [[passwordHashStrategy]] and
* uses `password_hash()` when available or `crypt()` when not.
*/
public $passwordHashStrategy;
/**
* @var int Default cost used for password hashing.
* Allowed value is between 4 and 31.
* @see generatePasswordHash()
* @since 2.0.6
*/
public $passwordHashCost = 13;
/**
* Encrypts data using a password.
* Derives keys for encryption and authentication from the password using PBKDF2 and a random salt,
* which is deliberately slow to protect against dictionary attacks. Use [[encryptByKey()]] to
* encrypt fast using a cryptographic key rather than a password. Key derivation time is
* determined by [[$derivationIterations]], which should be set as high as possible.
* The encrypted data includes a keyed message authentication code (MAC) so there is no need
* to hash input or output data.
* > Note: Avoid encrypting with passwords wherever possible. Nothing can protect against
* poor-quality or compromised passwords.
* @param string $data the data to encrypt
* @param string $password the password to use for encryption
* @return string the encrypted data
* @see decryptByPassword()
* @see encryptByKey()
*/
public function encryptByPassword($data, $password)
{
return $this->encrypt($data, true, $password, null);
}
/**
* Encrypts data using a cryptographic key.
* Derives keys for encryption and authentication from the input key using HKDF and a random salt,
* which is very fast relative to [[encryptByPassword()]]. The input key must be properly
* random -- use [[generateRandomKey()]] to generate keys.
* The encrypted data includes a keyed message authentication code (MAC) so there is no need
* to hash input or output data.
* @param string $data the data to encrypt
* @param string $inputKey the input to use for encryption and authentication
* @param string $info optional context and application specific information, see [[hkdf()]]
* @return string the encrypted data
* @see decryptByKey()
* @see encryptByPassword()
*/
public function encryptByKey($data, $inputKey, $info = null)
{
return $this->encrypt($data, false, $inputKey, $info);
}
/**
* Verifies and decrypts data encrypted with [[encryptByPassword()]].
* @param string $data the encrypted data to decrypt
* @param string $password the password to use for decryption
* @return bool|string the decrypted data or false on authentication failure
* @see encryptByPassword()
*/
public function decryptByPassword($data, $password)
{
return $this->decrypt($data, true, $password, null);
}
/**
* Verifies and decrypts data encrypted with [[encryptByKey()]].
* @param string $data the encrypted data to decrypt
* @param string $inputKey the input to use for encryption and authentication
* @param string $info optional context and application specific information, see [[hkdf()]]
* @return bool|string the decrypted data or false on authentication failure
* @see encryptByKey()
*/
public function decryptByKey($data, $inputKey, $info = null)
{
return $this->decrypt($data, false, $inputKey, $info);
}
/**
* Encrypts data.
*
* @param string $data data to be encrypted
* @param bool $passwordBased set true to use password-based key derivation
* @param string $secret the encryption password or key
* @param string $info context/application specific information, e.g. a user ID
* See [RFC 5869 Section 3.2](https://tools.ietf.org/html/rfc5869#section-3.2) for more details.
*
* @return string the encrypted data
* @throws InvalidConfigException on OpenSSL not loaded
* @throws Exception on OpenSSL error
* @see decrypt()
*/
protected function encrypt($data, $passwordBased, $secret, $info)
{
if (!extension_loaded('openssl')) {
throw new InvalidConfigException('Encryption requires the OpenSSL PHP extension');
}
if (!isset($this->allowedCiphers[$this->cipher][0], $this->allowedCiphers[$this->cipher][1])) {
throw new InvalidConfigException($this->cipher . ' is not an allowed cipher');
}
list($blockSize, $keySize) = $this->allowedCiphers[$this->cipher];
$keySalt = $this->generateRandomKey($keySize);
if ($passwordBased) {
$key = $this->pbkdf2($this->kdfHash, $secret, $keySalt, $this->derivationIterations, $keySize);
} else {
$key = $this->hkdf($this->kdfHash, $secret, $keySalt, $info, $keySize);
}
$iv = $this->generateRandomKey($blockSize);
$encrypted = openssl_encrypt($data, $this->cipher, $key, OPENSSL_RAW_DATA, $iv);
if ($encrypted === false) {
throw new \yii\base\Exception('OpenSSL failure on encryption: ' . openssl_error_string());
}
$authKey = $this->hkdf($this->kdfHash, $key, null, $this->authKeyInfo, $keySize);
$hashed = $this->hashData($iv . $encrypted, $authKey);
/*
* Output: [keySalt][MAC][IV][ciphertext]
* - keySalt is KEY_SIZE bytes long
* - MAC: message authentication code, length same as the output of MAC_HASH
* - IV: initialization vector, length $blockSize
*/
return $keySalt . $hashed;
}
/**
* Decrypts data.
*
* @param string $data encrypted data to be decrypted.
* @param bool $passwordBased set true to use password-based key derivation
* @param string $secret the decryption password or key
* @param string $info context/application specific information, @see encrypt()
*
* @return bool|string the decrypted data or false on authentication failure
* @throws InvalidConfigException on OpenSSL not loaded
* @throws Exception on OpenSSL error
* @see encrypt()
*/
protected function decrypt($data, $passwordBased, $secret, $info)
{
if (!extension_loaded('openssl')) {
throw new InvalidConfigException('Encryption requires the OpenSSL PHP extension');
}
if (!isset($this->allowedCiphers[$this->cipher][0], $this->allowedCiphers[$this->cipher][1])) {
throw new InvalidConfigException($this->cipher . ' is not an allowed cipher');
}
list($blockSize, $keySize) = $this->allowedCiphers[$this->cipher];
$keySalt = StringHelper::byteSubstr($data, 0, $keySize);
if ($passwordBased) {
$key = $this->pbkdf2($this->kdfHash, $secret, $keySalt, $this->derivationIterations, $keySize);
} else {
$key = $this->hkdf($this->kdfHash, $secret, $keySalt, $info, $keySize);
}
$authKey = $this->hkdf($this->kdfHash, $key, null, $this->authKeyInfo, $keySize);
$data = $this->validateData(StringHelper::byteSubstr($data, $keySize, null), $authKey);
if ($data === false) {
return false;
}
$iv = StringHelper::byteSubstr($data, 0, $blockSize);
$encrypted = StringHelper::byteSubstr($data, $blockSize, null);
$decrypted = openssl_decrypt($encrypted, $this->cipher, $key, OPENSSL_RAW_DATA, $iv);
if ($decrypted === false) {
throw new \yii\base\Exception('OpenSSL failure on decryption: ' . openssl_error_string());
}
return $decrypted;
}
/**
* Derives a key from the given input key using the standard HKDF algorithm.
* Implements HKDF specified in [RFC 5869](https://tools.ietf.org/html/rfc5869).
* Recommend use one of the SHA-2 hash algorithms: sha224, sha256, sha384 or sha512.
* @param string $algo a hash algorithm supported by `hash_hmac()`, e.g. 'SHA-256'
* @param string $inputKey the source key
* @param string $salt the random salt
* @param string $info optional info to bind the derived key material to application-
* and context-specific information, e.g. a user ID or API version, see
* [RFC 5869](https://tools.ietf.org/html/rfc5869)
* @param int $length length of the output key in bytes. If 0, the output key is
* the length of the hash algorithm output.
* @throws InvalidParamException when HMAC generation fails.
* @return string the derived key
*/
public function hkdf($algo, $inputKey, $salt = null, $info = null, $length = 0)
{
$test = @hash_hmac($algo, '', '', true);
if (!$test) {
throw new InvalidParamException('Failed to generate HMAC with hash algorithm: ' . $algo);
}
$hashLength = StringHelper::byteLength($test);
if (is_string($length) && preg_match('{^\d{1,16}$}', $length)) {
$length = (int) $length;
}
if (!is_int($length) || $length < 0 || $length > 255 * $hashLength) {
throw new InvalidParamException('Invalid length');
}
$blocks = $length !== 0 ? ceil($length / $hashLength) : 1;
if ($salt === null) {
$salt = str_repeat("\0", $hashLength);
}
$prKey = hash_hmac($algo, $inputKey, $salt, true);
$hmac = '';
$outputKey = '';
for ($i = 1; $i <= $blocks; $i++) {
$hmac = hash_hmac($algo, $hmac . $info . chr($i), $prKey, true);
$outputKey .= $hmac;
}
if ($length !== 0) {
$outputKey = StringHelper::byteSubstr($outputKey, 0, $length);
}
return $outputKey;
}
/**
* Derives a key from the given password using the standard PBKDF2 algorithm.
* Implements HKDF2 specified in [RFC 2898](http://tools.ietf.org/html/rfc2898#section-5.2)
* Recommend use one of the SHA-2 hash algorithms: sha224, sha256, sha384 or sha512.
* @param string $algo a hash algorithm supported by `hash_hmac()`, e.g. 'SHA-256'
* @param string $password the source password
* @param string $salt the random salt
* @param int $iterations the number of iterations of the hash algorithm. Set as high as
* possible to hinder dictionary password attacks.
* @param int $length length of the output key in bytes. If 0, the output key is
* the length of the hash algorithm output.
* @return string the derived key
* @throws InvalidParamException when hash generation fails due to invalid params given.
*/
public function pbkdf2($algo, $password, $salt, $iterations, $length = 0)
{
if (function_exists('hash_pbkdf2')) {
$outputKey = hash_pbkdf2($algo, $password, $salt, $iterations, $length, true);
if ($outputKey === false) {
throw new InvalidParamException('Invalid parameters to hash_pbkdf2()');
}
return $outputKey;
}
// todo: is there a nice way to reduce the code repetition in hkdf() and pbkdf2()?
$test = @hash_hmac($algo, '', '', true);
if (!$test) {
throw new InvalidParamException('Failed to generate HMAC with hash algorithm: ' . $algo);
}
if (is_string($iterations) && preg_match('{^\d{1,16}$}', $iterations)) {
$iterations = (int) $iterations;
}
if (!is_int($iterations) || $iterations < 1) {
throw new InvalidParamException('Invalid iterations');
}
if (is_string($length) && preg_match('{^\d{1,16}$}', $length)) {
$length = (int) $length;
}
if (!is_int($length) || $length < 0) {
throw new InvalidParamException('Invalid length');
}
$hashLength = StringHelper::byteLength($test);
$blocks = $length !== 0 ? ceil($length / $hashLength) : 1;
$outputKey = '';
for ($j = 1; $j <= $blocks; $j++) {
$hmac = hash_hmac($algo, $salt . pack('N', $j), $password, true);
$xorsum = $hmac;
for ($i = 1; $i < $iterations; $i++) {
$hmac = hash_hmac($algo, $hmac, $password, true);
$xorsum ^= $hmac;
}
$outputKey .= $xorsum;
}
if ($length !== 0) {
$outputKey = StringHelper::byteSubstr($outputKey, 0, $length);
}
return $outputKey;
}
/**
* Prefixes data with a keyed hash value so that it can later be detected if it is tampered.
* There is no need to hash inputs or outputs of [[encryptByKey()]] or [[encryptByPassword()]]
* as those methods perform the task.
* @param string $data the data to be protected
* @param string $key the secret key to be used for generating hash. Should be a secure
* cryptographic key.
* @param bool $rawHash whether the generated hash value is in raw binary format. If false, lowercase
* hex digits will be generated.
* @return string the data prefixed with the keyed hash
* @throws InvalidConfigException when HMAC generation fails.
* @see validateData()
* @see generateRandomKey()
* @see hkdf()
* @see pbkdf2()
*/
public function hashData($data, $key, $rawHash = false)
{
$hash = hash_hmac($this->macHash, $data, $key, $rawHash);
if (!$hash) {
throw new InvalidConfigException('Failed to generate HMAC with hash algorithm: ' . $this->macHash);
}
return $hash . $data;
}
/**
* Validates if the given data is tampered.
* @param string $data the data to be validated. The data must be previously
* generated by [[hashData()]].
* @param string $key the secret key that was previously used to generate the hash for the data in [[hashData()]].
* function to see the supported hashing algorithms on your system. This must be the same
* as the value passed to [[hashData()]] when generating the hash for the data.
* @param bool $rawHash this should take the same value as when you generate the data using [[hashData()]].
* It indicates whether the hash value in the data is in binary format. If false, it means the hash value consists
* of lowercase hex digits only.
* hex digits will be generated.
* @return string the real data with the hash stripped off. False if the data is tampered.
* @throws InvalidConfigException when HMAC generation fails.
* @see hashData()
*/
public function validateData($data, $key, $rawHash = false)
{
$test = @hash_hmac($this->macHash, '', '', $rawHash);
if (!$test) {
throw new InvalidConfigException('Failed to generate HMAC with hash algorithm: ' . $this->macHash);
}
$hashLength = StringHelper::byteLength($test);
if (StringHelper::byteLength($data) >= $hashLength) {
$hash = StringHelper::byteSubstr($data, 0, $hashLength);
$pureData = StringHelper::byteSubstr($data, $hashLength, null);
$calculatedHash = hash_hmac($this->macHash, $pureData, $key, $rawHash);
if ($this->compareString($hash, $calculatedHash)) {
return $pureData;
}
}
return false;
}
private $_useLibreSSL;
private $_randomFile;
/**
* Generates specified number of random bytes.
* Note that output may not be ASCII.
* @see generateRandomString() if you need a string.
*
* @param int $length the number of bytes to generate
* @return string the generated random bytes
* @throws InvalidParamException if wrong length is specified
* @throws Exception on failure.
*/
public function generateRandomKey($length = 32)
{
if (!is_int($length)) {
throw new InvalidParamException('First parameter ($length) must be an integer');
}
if ($length < 1) {
throw new InvalidParamException('First parameter ($length) must be greater than 0');
}
// always use random_bytes() if it is available
if (function_exists('random_bytes')) {
return random_bytes($length);
}
// The recent LibreSSL RNGs are faster and likely better than /dev/urandom.
// Parse OPENSSL_VERSION_TEXT because OPENSSL_VERSION_NUMBER is no use for LibreSSL.
// https://bugs.php.net/bug.php?id=71143
if ($this->_useLibreSSL === null) {
$this->_useLibreSSL = defined('OPENSSL_VERSION_TEXT')
&& preg_match('{^LibreSSL (\d\d?)\.(\d\d?)\.(\d\d?)$}', OPENSSL_VERSION_TEXT, $matches)
&& (10000 * $matches[1]) + (100 * $matches[2]) + $matches[3] >= 20105;
}
// Since 5.4.0, openssl_random_pseudo_bytes() reads from CryptGenRandom on Windows instead
// of using OpenSSL library. LibreSSL is OK everywhere but don't use OpenSSL on non-Windows.
if ($this->_useLibreSSL
|| (
DIRECTORY_SEPARATOR !== '/'
&& substr_compare(PHP_OS, 'win', 0, 3, true) === 0
&& function_exists('openssl_random_pseudo_bytes')
)
) {
$key = openssl_random_pseudo_bytes($length, $cryptoStrong);
if ($cryptoStrong === false) {
throw new Exception(
'openssl_random_pseudo_bytes() set $crypto_strong false. Your PHP setup is insecure.'
);
}
if ($key !== false && StringHelper::byteLength($key) === $length) {
return $key;
}
}
// mcrypt_create_iv() does not use libmcrypt. Since PHP 5.3.7 it directly reads
// CryptGenRandom on Windows. Elsewhere it directly reads /dev/urandom.
if (function_exists('mcrypt_create_iv')) {
$key = mcrypt_create_iv($length, MCRYPT_DEV_URANDOM);
if (StringHelper::byteLength($key) === $length) {
return $key;
}
}
// If not on Windows, try to open a random device.
if ($this->_randomFile === null && DIRECTORY_SEPARATOR === '/') {
// urandom is a symlink to random on FreeBSD.
$device = PHP_OS === 'FreeBSD' ? '/dev/random' : '/dev/urandom';
// Check random device for special character device protection mode. Use lstat()
// instead of stat() in case an attacker arranges a symlink to a fake device.
$lstat = @lstat($device);
if ($lstat !== false && ($lstat['mode'] & 0170000) === 020000) {
$this->_randomFile = fopen($device, 'rb') ?: null;
if (is_resource($this->_randomFile)) {
// Reduce PHP stream buffer from default 8192 bytes to optimize data
// transfer from the random device for smaller values of $length.
// This also helps to keep future randoms out of user memory space.
$bufferSize = 8;
if (function_exists('stream_set_read_buffer')) {
stream_set_read_buffer($this->_randomFile, $bufferSize);
}
// stream_set_read_buffer() isn't implemented on HHVM
if (function_exists('stream_set_chunk_size')) {
stream_set_chunk_size($this->_randomFile, $bufferSize);
}
}
}
}
if (is_resource($this->_randomFile)) {
$buffer = '';
$stillNeed = $length;
while ($stillNeed > 0) {
$someBytes = fread($this->_randomFile, $stillNeed);
if ($someBytes === false) {
break;
}
$buffer .= $someBytes;
$stillNeed -= StringHelper::byteLength($someBytes);
if ($stillNeed === 0) {
// Leaving file pointer open in order to make next generation faster by reusing it.
return $buffer;
}
}
fclose($this->_randomFile);
$this->_randomFile = null;
}
throw new Exception('Unable to generate a random key');
}
/**
* Generates a random string of specified length.
* The string generated matches [A-Za-z0-9_-]+ and is transparent to URL-encoding.
*
* @param int $length the length of the key in characters
* @return string the generated random key
* @throws Exception on failure.
*/
public function generateRandomString($length = 32)
{
if (!is_int($length)) {
throw new InvalidParamException('First parameter ($length) must be an integer');
}
if ($length < 1) {
throw new InvalidParamException('First parameter ($length) must be greater than 0');
}
$bytes = $this->generateRandomKey($length);
// '=' character(s) returned by base64_encode() are always discarded because
// they are guaranteed to be after position $length in the base64_encode() output.
return strtr(substr(base64_encode($bytes), 0, $length), '+/', '_-');
}
/**
* Generates a secure hash from a password and a random salt.
*
* The generated hash can be stored in database.
* Later when a password needs to be validated, the hash can be fetched and passed
* to [[validatePassword()]]. For example,
*
* ```php
* // generates the hash (usually done during user registration or when the password is changed)
* $hash = Yii::$app->getSecurity()->generatePasswordHash($password);
* // ...save $hash in database...
*
* // during login, validate if the password entered is correct using $hash fetched from database
* if (Yii::$app->getSecurity()->validatePassword($password, $hash) {
* // password is good
* } else {
* // password is bad
* }
* ```
*
* @param string $password The password to be hashed.
* @param int $cost Cost parameter used by the Blowfish hash algorithm.
* The higher the value of cost,
* the longer it takes to generate the hash and to verify a password against it. Higher cost
* therefore slows down a brute-force attack. For best protection against brute-force attacks,
* set it to the highest value that is tolerable on production servers. The time taken to
* compute the hash doubles for every increment by one of $cost.
* @return string The password hash string. When [[passwordHashStrategy]] is set to 'crypt',
* the output is always 60 ASCII characters, when set to 'password_hash' the output length
* might increase in future versions of PHP (http://php.net/manual/en/function.password-hash.php)
* @throws Exception on bad password parameter or cost parameter.
* @see validatePassword()
*/
public function generatePasswordHash($password, $cost = null)
{
if ($cost === null) {
$cost = $this->passwordHashCost;
}
if (function_exists('password_hash')) {
/** @noinspection PhpUndefinedConstantInspection */
return password_hash($password, PASSWORD_DEFAULT, ['cost' => $cost]);
}
$salt = $this->generateSalt($cost);
$hash = crypt($password, $salt);
// strlen() is safe since crypt() returns only ascii
if (!is_string($hash) || strlen($hash) !== 60) {
throw new Exception('Unknown error occurred while generating hash.');
}
return $hash;
}
/**
* Verifies a password against a hash.
* @param string $password The password to verify.
* @param string $hash The hash to verify the password against.
* @return bool whether the password is correct.
* @throws InvalidParamException on bad password/hash parameters or if crypt() with Blowfish hash is not available.
* @see generatePasswordHash()
*/
public function validatePassword($password, $hash)
{
if (!is_string($password) || $password === '') {
throw new InvalidParamException('Password must be a string and cannot be empty.');
}
if (!preg_match('/^\$2[axy]\$(\d\d)\$[\.\/0-9A-Za-z]{22}/', $hash, $matches)
|| $matches[1] < 4
|| $matches[1] > 30
) {
throw new InvalidParamException('Hash is invalid.');
}
if (function_exists('password_verify')) {
return password_verify($password, $hash);
}
$test = crypt($password, $hash);
$n = strlen($test);
if ($n !== 60) {
return false;
}
return $this->compareString($test, $hash);
}
/**
* Generates a salt that can be used to generate a password hash.
*
* The PHP [crypt()](http://php.net/manual/en/function.crypt.php) built-in function
* requires, for the Blowfish hash algorithm, a salt string in a specific format:
* "$2a$", "$2x$" or "$2y$", a two digit cost parameter, "$", and 22 characters
* from the alphabet "./0-9A-Za-z".
*
* @param int $cost the cost parameter
* @return string the random salt value.
* @throws InvalidParamException if the cost parameter is out of the range of 4 to 31.
*/
protected function generateSalt($cost = 13)
{
$cost = (int) $cost;
if ($cost < 4 || $cost > 31) {
throw new InvalidParamException('Cost must be between 4 and 31.');
}
// Get a 20-byte random string
$rand = $this->generateRandomKey(20);
// Form the prefix that specifies Blowfish (bcrypt) algorithm and cost parameter.
$salt = sprintf("$2y$%02d$", $cost);
// Append the random salt data in the required base64 format.
$salt .= str_replace('+', '.', substr(base64_encode($rand), 0, 22));
return $salt;
}
/**
* Performs string comparison using timing attack resistant approach.
* @see http://codereview.stackexchange.com/questions/13512
* @param string $expected string to compare.
* @param string $actual user-supplied string.
* @return bool whether strings are equal.
*/
public function compareString($expected, $actual)
{
$expected .= "\0";
$actual .= "\0";
$expectedLength = StringHelper::byteLength($expected);
$actualLength = StringHelper::byteLength($actual);
$diff = $expectedLength - $actualLength;
for ($i = 0; $i < $actualLength; $i++) {
$diff |= (ord($actual[$i]) ^ ord($expected[$i % $expectedLength]));
}
return $diff === 0;
}
}