class PhpassHashedPassword

class PhpassHashedPassword implements PasswordInterface {
    
    /**
     * The minimum allowed log2 number of iterations for password stretching.
     */
    const MIN_HASH_COUNT = 7;
    
    /**
     * The maximum allowed log2 number of iterations for password stretching.
     */
    const MAX_HASH_COUNT = 30;
    
    /**
     * The expected (and maximum) number of characters in a hashed password.
     */
    const HASH_LENGTH = 55;
    
    /**
     * Returns a string for mapping an int to the corresponding base 64 character.
     *
     * @var string
     */
    public static $ITOA64 = './0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
    
    /**
     * Password stretching iteration count.
     *
     * Specifies the number of times the hashing function will be applied when
     * generating new password hashes. The number of times is calculated by
     * raising 2 to the power of the given value.
     *
     * @var int
     */
    protected $countLog2;
    
    /**
     * Constructs a new password hashing instance.
     *
     * @param int $countLog2
     *   Password stretching iteration count. Specifies the number of times the
     *   hashing function will be applied when generating new password hashes.
     *   The number of times is calculated by raising 2 to the power of the given
     *   value.
     */
    public function __construct($countLog2) {
        // Ensure that $countLog2 is within set bounds.
        $this->countLog2 = $this->enforceLog2Boundaries($countLog2);
    }
    
    /**
     * Encodes bytes into printable base 64 using the *nix standard from crypt().
     *
     * @param string $input
     *   The string containing bytes to encode.
     * @param int $count
     *   The number of characters (bytes) to encode.
     *
     * @return string
     *   Encoded string.
     */
    protected function base64Encode($input, $count) {
        $output = '';
        $i = 0;
        do {
            $value = ord($input[$i++]);
            $output .= static::$ITOA64[$value & 0x3f];
            if ($i < $count) {
                $value |= ord($input[$i]) << 8;
            }
            $output .= static::$ITOA64[$value >> 6 & 0x3f];
            if ($i++ >= $count) {
                break;
            }
            if ($i < $count) {
                $value |= ord($input[$i]) << 16;
            }
            $output .= static::$ITOA64[$value >> 12 & 0x3f];
            if ($i++ >= $count) {
                break;
            }
            $output .= static::$ITOA64[$value >> 18 & 0x3f];
        } while ($i < $count);
        return $output;
    }
    
    /**
     * Generates a random base 64-encoded salt prefixed with hash settings.
     *
     * Proper use of salts may defeat a number of attacks, including:
     *  - The ability to try candidate passwords against multiple hashes at once.
     *  - The ability to use pre-hashed lists of candidate passwords.
     *  - The ability to determine whether two users have the same (or different)
     *    password without actually having to guess one of the passwords.
     *
     * @return string
     *   A 12 character string containing the iteration count and a random salt.
     */
    protected function generateSalt() {
        $output = '$S$';
        // We encode the final log2 iteration count in base 64.
        $output .= static::$ITOA64[$this->countLog2];
        // 6 bytes is the standard salt for a portable phpass hash.
        $output .= $this->base64Encode(random_bytes(6), 6);
        return $output;
    }
    
    /**
     * Ensures that $count_log2 is within set bounds.
     *
     * @param int $count_log2
     *   Integer that determines the number of iterations used in the hashing
     *   process. A larger value is more secure, but takes more time to complete.
     *
     * @return int
     *   Integer within set bounds that is closest to $count_log2.
     */
    protected function enforceLog2Boundaries($count_log2) {
        if ($count_log2 < static::MIN_HASH_COUNT) {
            return static::MIN_HASH_COUNT;
        }
        elseif ($count_log2 > static::MAX_HASH_COUNT) {
            return static::MAX_HASH_COUNT;
        }
        return (int) $count_log2;
    }
    
    /**
     * Hash a password using a secure stretched hash.
     *
     * By using a salt and repeated hashing the password is "stretched". Its
     * security is increased because it becomes much more computationally costly
     * for an attacker to try to break the hash by brute-force computation of the
     * hashes of a large number of plain-text words or strings to find a match.
     *
     * @param string $algo
     *   The string name of a hashing algorithm usable by hash(), like 'sha256'.
     * @param string $password
     *   Plain-text password up to 512 bytes (128 to 512 UTF-8 characters) to
     *   hash.
     * @param string $setting
     *   An existing hash or the output of $this->generateSalt(). Must be at least
     *   12 characters (the settings and salt).
     *
     * @return string
     *   A string containing the hashed password (and salt) or FALSE on failure.
     *   The return string will be truncated at HASH_LENGTH characters max.
     */
    protected function crypt($algo, $password, $setting) {
        // Prevent DoS attacks by refusing to hash large passwords.
        if (strlen($password) > PasswordInterface::PASSWORD_MAX_LENGTH) {
            return FALSE;
        }
        // The first 12 characters of an existing hash are its setting string.
        $setting = substr($setting, 0, 12);
        if ($setting[0] != '$' || $setting[2] != '$') {
            return FALSE;
        }
        $count_log2 = $this->getCountLog2($setting);
        // Stored hashes may have been encrypted with any iteration count. However
        // we do not allow applying the algorithm for unreasonable low and high
        // values respectively.
        if ($count_log2 != $this->enforceLog2Boundaries($count_log2)) {
            return FALSE;
        }
        $salt = substr($setting, 4, 8);
        // Hashes must have an 8 character salt.
        if (strlen($salt) != 8) {
            return FALSE;
        }
        // Convert the base 2 logarithm into an integer.
        $count = 1 << $count_log2;
        $hash = hash($algo, $salt . $password, TRUE);
        do {
            $hash = hash($algo, $hash . $password, TRUE);
        } while (--$count);
        $len = strlen($hash);
        $output = $setting . $this->base64Encode($hash, $len);
        // $this->base64Encode() of a 16 byte MD5 will always be 22 characters.
        // $this->base64Encode() of a 64 byte sha512 will always be 86 characters.
        $expected = 12 + ceil(8 * $len / 6);
        return strlen($output) == $expected ? substr($output, 0, static::HASH_LENGTH) : FALSE;
    }
    
    /**
     * Parses the log2 iteration count from a stored hash or setting string.
     *
     * @param string $setting
     *   An existing hash or the output of $this->generateSalt(). Must be at least
     *   12 characters (the settings and salt).
     *
     * @return int
     *   The log2 iteration count.
     */
    public function getCountLog2($setting) {
        return strpos(static::$ITOA64, $setting[3]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function hash($password) {
        return $this->crypt('sha512', $password, $this->generateSalt());
    }
    
    /**
     * {@inheritdoc}
     */
    public function check($password, $hash) {
        if (substr($hash, 0, 2) == 'U$') {
            // This may be an updated password from user_update_7000(). Such hashes
            // have 'U' added as the first character and need an extra md5() (see the
            // Drupal 7 documentation).
            $stored_hash = substr($hash, 1);
            $password = md5($password);
        }
        else {
            $stored_hash = $hash;
        }
        $type = substr($stored_hash, 0, 3);
        switch ($type) {
            case '$S$':
                // A normal Drupal 7 password using sha512.
                $computed_hash = $this->crypt('sha512', $password, $stored_hash);
                break;
            case '$H$':
            // phpBB3 uses "$H$" for the same thing as "$P$".
            case '$P$':
                // A phpass password generated using md5.  This is an
                // imported password or from an earlier Drupal version.
                $computed_hash = $this->crypt('md5', $password, $stored_hash);
                break;
            default:
                return FALSE;
        }
        // Compare using hash_equals() instead of === to mitigate timing attacks.
        return $computed_hash && hash_equals($stored_hash, $computed_hash);
    }
    
    /**
     * {@inheritdoc}
     */
    public function needsRehash($hash) {
        // Check whether this was an updated password.
        if (substr($hash, 0, 3) != '$S$' || strlen($hash) != static::HASH_LENGTH) {
            return TRUE;
        }
        // Ensure that $count_log2 is within set bounds.
        $count_log2 = $this->enforceLog2Boundaries($this->countLog2);
        // Check whether the iteration count used differs from the standard number.
        return $this->getCountLog2($hash) !== $count_log2;
    }

}