<?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: [[encrypt()]] and [[decrypt()]]
 * - Data tampering prevention: [[hashData()]] and [[validateData()]]
 * - Password validation: [[generatePasswordHash()]] and [[validatePassword()]]
 *
 * Additionally, Security provides [[getSecretKey()]] to support generating
 * named secret keys. These secret keys, once generated, will be stored in a file
 * and made available in future requests.
 *
 * @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 integer crypt block size in bytes.
     * For AES-128, AES-192, block size is 128-bit (16 bytes).
     * For AES-256, block size is 256-bit (32 bytes).
     * Recommended value: 32
     */
    public $cryptBlockSize = 32;
    /**
     * @var integer crypt key size in bytes.
     * For AES-192, key size is 192-bit (24 bytes).
     * For AES-256, key size is 256-bit (32 bytes).
     * Recommended value: 32
     */
    public $cryptKeySize = 32;
    /**
     * @var string derivation hash algorithm name.
     * Recommended value: 'sha256'
     */
    public $derivationHash = 'sha256';
    /**
     * @var integer derivation iterations count.
     * Recommended value: 1000000
     */
    public $derivationIterations = 1000000;
    /**
     * @var string strategy, which should be used to derive a key for encryption.
     * Available strategies:
     * - 'pbkdf2' - PBKDF2 key derivation, this option is recommended, but it requires PHP version >= 5.5.0
     * - 'hmac' - HMAC hash key derivation.
     */
    public $deriveKeyStrategy = 'hmac';

    /**
     * Encrypts data.
     * @param string $data data to be encrypted.
     * @param string $password the encryption password
     * @return string the encrypted data
     * @throws Exception if PHP Mcrypt extension is not loaded or failed to be initialized
     * @see decrypt()
     */
    public function encrypt($data, $password)
    {
        $module = $this->openCryptModule();
        $data = $this->addPadding($data);
        $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($module), MCRYPT_DEV_URANDOM);
        $key = $this->deriveKey($password, $iv);
        mcrypt_generic_init($module, $key, $iv);
        $encrypted = $iv . mcrypt_generic($module, $data);
        mcrypt_generic_deinit($module);
        mcrypt_module_close($module);

        return $encrypted;
    }

    /**
     * Decrypts data
     * @param string $data data to be decrypted.
     * @param string $password the decryption password
     * @return string the decrypted data
     * @throws Exception if PHP Mcrypt extension is not loaded or failed to be initialized
     * @see encrypt()
     */
    public function decrypt($data, $password)
    {
        if ($data === null) {
            return null;
        }
        $module = $this->openCryptModule();
        $ivSize = mcrypt_enc_get_iv_size($module);
        $iv = StringHelper::byteSubstr($data, 0, $ivSize);
        $key = $this->deriveKey($password, $iv);
        mcrypt_generic_init($module, $key, $iv);
        $decrypted = mdecrypt_generic($module, StringHelper::byteSubstr($data, $ivSize, StringHelper::byteLength($data)));
        mcrypt_generic_deinit($module);
        mcrypt_module_close($module);

        return $this->stripPadding($decrypted);
    }

    /**
     * Adds a padding to the given data (PKCS #7).
     * @param string $data the data to pad
     * @return string the padded data
     */
    protected function addPadding($data)
    {
        $pad = $this->cryptBlockSize - (StringHelper::byteLength($data) % $this->cryptBlockSize);

        return $data . str_repeat(chr($pad), $pad);
    }

    /**
     * Strips the padding from the given data.
     * @param string $data the data to trim
     * @return string the trimmed data
     */
    protected function stripPadding($data)
    {
        $end = StringHelper::byteSubstr($data, -1, null);
        $last = ord($end);
        $n = StringHelper::byteLength($data) - $last;
        if (StringHelper::byteSubstr($data, $n, null) == str_repeat($end, $last)) {
            return StringHelper::byteSubstr($data, 0, $n);
        }

        return false;
    }

    /**
     * Derives a key from the given password (PBKDF2).
     * @param string $password the source password
     * @param string $salt the random salt
     * @throws InvalidConfigException if unsupported derive key strategy is configured.
     * @return string the derived key
     */
    protected function deriveKey($password, $salt)
    {
        switch ($this->deriveKeyStrategy) {
            case 'pbkdf2':
                return $this->deriveKeyPbkdf2($password, $salt);
            case 'hmac':
                return $this->deriveKeyHmac($password, $salt);
            default:
                throw new InvalidConfigException("Unknown Derive key strategy '{$this->deriveKeyStrategy}'");
        }
    }

    /**
     * Derives a key from the given password using PBKDF2.
     * @param string $password the source password
     * @param string $salt the random salt
     * @throws InvalidConfigException if environment does not allows PBKDF2.
     * @return string the derived key
     */
    protected function deriveKeyPbkdf2($password, $salt)
    {
        if (function_exists('hash_pbkdf2')) {
            return hash_pbkdf2($this->derivationHash, $password, $salt, $this->derivationIterations, $this->cryptKeySize, true);
        } else {
            throw new InvalidConfigException('Derive key strategy "pbkdf2" requires PHP >= 5.5.0, either upgrade your environment or use another strategy.');
        }
    }

    /**
     * Derives a key from the given password using HMAC.
     * @param string $password the source password
     * @param string $salt the random salt
     * @return string the derived key
     */
    protected function deriveKeyHmac($password, $salt)
    {
        $hmac = hash_hmac($this->derivationHash, $salt . pack('N', 1), $password, true);
        $xorsum  = $hmac;
        for ($i = 1; $i < $this->derivationIterations; $i++) {
            $hmac = hash_hmac($this->derivationHash, $hmac, $password, true);
            $xorsum ^= $hmac;
        }
        return substr($xorsum, 0, $this->cryptKeySize);
    }

    /**
     * Prefixes data with a keyed hash value so that it can later be detected if it is tampered.
     * @param string $data the data to be protected
     * @param string $key the secret key to be used for generating hash
     * @param string $algorithm the hashing algorithm (e.g. "md5", "sha1", "sha256", etc.). Call PHP "hash_algos()"
     * function to see the supported hashing algorithms on your system.
     * @return string the data prefixed with the keyed hash
     * @see validateData()
     * @see getSecretKey()
     */
    public function hashData($data, $key, $algorithm = 'sha256')
    {
        return hash_hmac($algorithm, $data, $key) . $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()]].
     * @param string $algorithm the hashing algorithm (e.g. "md5", "sha1", "sha256", etc.). Call PHP "hash_algos()"
     * function to see the supported hashing algorithms on your system. This must be the same
     * as the value passed to [[hashData()]] when generating the hash for the data.
     * @return string the real data with the hash stripped off. False if the data is tampered.
     * @see hashData()
     */
    public function validateData($data, $key, $algorithm = 'sha256')
    {
        $hashSize = StringHelper::byteLength(hash_hmac($algorithm, 'test', $key));
        $n = StringHelper::byteLength($data);
        if ($n >= $hashSize) {
            $hash = StringHelper::byteSubstr($data, 0, $hashSize);
            $pureData = StringHelper::byteSubstr($data, $hashSize, $n - $hashSize);

            $calculatedHash = hash_hmac($algorithm, $pureData, $key);

            if ($this->compareString($hash, $calculatedHash)) {
                return $pureData;
            } else {
                return false;
            }
        } else {
            return false;
        }
    }

    /**
     * Returns a secret key associated with the specified name.
     * If the secret key does not exist, a random key will be generated
     * and saved in the file "keys.json" under the application's runtime directory
     * so that the same secret key can be returned in future requests.
     * @param string $name the name that is associated with the secret key
     * @param integer $length the length of the key that should be generated if not exists
     * @return string the secret key associated with the specified name
     */
    public function getSecretKey($name, $length = 32)
    {
        static $keys;
        $keyFile = Yii::$app->getRuntimePath() . '/keys.json';
        if ($keys === null) {
            $keys = [];
            if (is_file($keyFile)) {
                $keys = json_decode(file_get_contents($keyFile), true);
            }
        }
        if (!isset($keys[$name])) {
            $keys[$name] = $this->generateRandomKey($length);
            file_put_contents($keyFile, json_encode($keys));
        }

        return $keys[$name];
    }

    /**
     * Generates a random key. The key may contain uppercase and lowercase latin letters, digits, underscore, dash and dot.
     * Note: for delivering high security key, this method requires PHP 'mcrypt' extension.
     * @param integer $length the length of the key that should be generated
     * @return string the generated random key
     */
    public function generateRandomKey($length = 32)
    {
        if (function_exists('mcrypt_create_iv')) {
            return mcrypt_create_iv($length, MCRYPT_DEV_URANDOM);
        }
        $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-.';
        return substr(str_shuffle(str_repeat($chars, 5)), 0, $length);
    }

    /**
     * Opens the mcrypt module.
     * @return resource the mcrypt module handle.
     * @throws InvalidConfigException if mcrypt extension is not installed
     * @throws Exception if mcrypt initialization fails
     */
    protected function openCryptModule()
    {
        if (!extension_loaded('mcrypt')) {
            throw new InvalidConfigException('The mcrypt PHP extension is not installed.');
        }
        // AES version depending on crypt block size
        $algorithmName = 'rijndael-' . ($this->cryptBlockSize * 8);
        $module = @mcrypt_module_open($algorithmName, '', 'cbc', '');
        if ($module === false) {
            throw new Exception('Failed to initialize the mcrypt module.');
        }

        return $module;
    }

    /**
     * Generates a secure hash from a password and a random salt.
     *
     * The generated hash can be stored in database (e.g. `CHAR(64) CHARACTER SET latin1` on MySQL).
     * Later when a password needs to be validated, the hash can be fetched and passed
     * to [[validatePassword()]]. For example,
     *
     * ~~~
     * // 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 integer $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 for 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. So, for example, if the
     * hash takes 1 second to compute when $cost is 14 then then the compute time varies as
     * 2^($cost - 14) seconds.
     * @throws Exception on bad password parameter or cost parameter
     * @return string The password hash string, ASCII and not longer than 64 characters.
     * @see validatePassword()
     */
    public function generatePasswordHash($password, $cost = 13)
    {
        $salt = $this->generateSalt($cost);
        $hash = crypt($password, $salt);

        if (!is_string($hash) || strlen($hash) < 32) {
            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 $hash The hash to verify the password against.
     * @return boolean whether the password is correct.
     * @throws InvalidParamException on bad password or hash parameters or if crypt() with Blowfish hash is not available.
     * @see generatePasswordHash()
     */
    public function validatePassword($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.');
        }

        $test = crypt($password, $hash);
        $n = strlen($test);
        if ($n < 32 || $n !== strlen($hash)) {
            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 integer $cost the cost parameter
     * @return string the random salt value.
     * @throws InvalidParamException if the cost parameter is not between 4 and 31
     */
    protected function generateSalt($cost = 13)
    {
        $cost = (int) $cost;
        if ($cost < 4 || $cost > 31) {
            throw new InvalidParamException('Cost must be between 4 and 31.');
        }

        // Get 20 * 8bits of random entropy
        $rand = $this->generateRandomKey(20);

        // Add the microtime for a little more entropy.
        $rand .= microtime(true);
        // Mix the bits cryptographically into a 20-byte binary string.
        $rand = sha1($rand, true);
        // Form the prefix that specifies Blowfish 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 $actual string to compare.
     * @return boolean whether strings are equal.
     */
    protected function compareString($expected, $actual)
    {
        // timing attack resistant approach:
        $diff = 0;
        for ($i = 0; $i < StringHelper::byteLength($actual); $i++) {
            $diff |= (ord($actual[$i]) ^ ord($expected[$i]));
        }
        return $diff === 0;
    }
}