framework/base/Security.php
public function generateRandomKey($length = 32)
    {
        if (!is_int($length)) {
            throw new InvalidArgumentException('First parameter ($length) must be an integer');
        }

        if ($length < 1) {
            throw new InvalidArgumentException('First parameter ($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 (function_exists('openssl_random_pseudo_bytes')
            && ($this->_useLibreSSL
            || (
                DIRECTORY_SEPARATOR !== '/'
                && substr_compare(PHP_OS, 'win', 0, 3, true) === 0
            ))
        ) {
            $key = openssl_random_pseudo_bytes($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');
    }
public function generateRandomKey($length = 32)
    {
        if (!is_int($length)) {
            throw new InvalidArgumentException('First parameter ($length) must be an integer');
        }

        if ($length < 1) {
            throw new InvalidArgumentException('First parameter ($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 (function_exists('openssl_random_pseudo_bytes')
            && ($this->_useLibreSSL
            || (
                DIRECTORY_SEPARATOR !== '/'
                && substr_compare(PHP_OS, 'win', 0, 3, true) === 0
            ))
        ) {
            $key = openssl_random_pseudo_bytes($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 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 InvalidArgumentException if wrong length is specified
@throws Exception on failure.