password.inc

<?php


/**
 * @file
 * Secure password hashing functions for user authentication.
 *
 * Based on the Portable PHP password hashing framework.
 * @see http://www.openwall.com/phpass/
 *
 * An alternative or custom version of this password hashing API may be
 * used by setting the variable password_inc to the name of the PHP file
 * containing replacement user_hash_password(), user_check_password(), and
 * user_needs_new_hash() functions.
 */

/**
 * The standard log2 number of iterations for password stretching. This should
 * increase by 1 every Drupal version in order to counteract increases in the
 * speed and power of computers available to crack the hashes.
 */
define('DRUPAL_HASH_COUNT', 15);

/**
 * The minimum allowed log2 number of iterations for password stretching.
 */
define('DRUPAL_MIN_HASH_COUNT', 7);

/**
 * The maximum allowed log2 number of iterations for password stretching.
 */
define('DRUPAL_MAX_HASH_COUNT', 30);

/**
 * The expected (and maximum) number of characters in a hashed password.
 */
define('DRUPAL_HASH_LENGTH', 55);

/**
 * Returns a string for mapping an int to the corresponding base 64 character.
 */
function _password_itoa64() {
    return './0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
}

/**
 * Encodes bytes into printable base 64 using the *nix standard from crypt().
 *
 * @param $input
 *   The string containing bytes to encode.
 * @param $count
 *   The number of characters (bytes) to encode.
 *
 * @return
 *   Encoded string
 */
function _password_base64_encode($input, $count) {
    $output = '';
    $i = 0;
    $itoa64 = _password_itoa64();
    do {
        $value = ord($input[$i++]);
        $output .= $itoa64[$value & 0x3f];
        if ($i < $count) {
            $value |= ord($input[$i]) << 8;
        }
        $output .= $itoa64[$value >> 6 & 0x3f];
        if ($i++ >= $count) {
            break;
        }
        if ($i < $count) {
            $value |= ord($input[$i]) << 16;
        }
        $output .= $itoa64[$value >> 12 & 0x3f];
        if ($i++ >= $count) {
            break;
        }
        $output .= $itoa64[$value >> 18 & 0x3f];
    } while ($i < $count);
    return $output;
}

/**
 * Generates a random base 64-encoded salt prefixed with settings for the hash.
 *
 * 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.
 *
 * @param $count_log2
 *   Integer that determines the number of iterations used in the hashing
 *   process. A larger value is more secure, but takes more time to complete.
 *
 * @return
 *   A 12 character string containing the iteration count and a random salt.
 */
function _password_generate_salt($count_log2) {
    $output = '$S$';
    // Ensure that $count_log2 is within set bounds.
    $count_log2 = _password_enforce_log2_boundaries($count_log2);
    // We encode the final log2 iteration count in base 64.
    $itoa64 = _password_itoa64();
    $output .= $itoa64[$count_log2];
    // 6 bytes is the standard salt for a portable phpass hash.
    $output .= _password_base64_encode(drupal_random_bytes(6), 6);
    return $output;
}

/**
 * Ensures that $count_log2 is within set bounds.
 *
 * @param $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
 *   Integer within set bounds that is closest to $count_log2.
 */
function _password_enforce_log2_boundaries($count_log2) {
    if ($count_log2 < DRUPAL_MIN_HASH_COUNT) {
        return DRUPAL_MIN_HASH_COUNT;
    }
    elseif ($count_log2 > DRUPAL_MAX_HASH_COUNT) {
        return DRUPAL_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 $algo
 *   The string name of a hashing algorithm usable by hash(), like 'sha256'.
 * @param $password
 *   Plain-text password up to 512 bytes (128 to 512 UTF-8 characters) to hash.
 * @param $setting
 *   An existing hash or the output of _password_generate_salt().  Must be
 *   at least 12 characters (the settings and salt).
 *
 * @return
 *   A string containing the hashed password (and salt) or FALSE on failure.
 *   The return string will be truncated at DRUPAL_HASH_LENGTH characters max.
 */
function _password_crypt($algo, $password, $setting) {
    // Prevent DoS attacks by refusing to hash large passwords.
    if (strlen($password) > 512) {
        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;
    }
    $count_log2 = _password_get_count_log2($setting);
    // Hashes may be imported from elsewhere, so we allow != DRUPAL_HASH_COUNT
    if ($count_log2 < DRUPAL_MIN_HASH_COUNT || $count_log2 > DRUPAL_MAX_HASH_COUNT) {
        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;
    // We rely on the hash() function being available in PHP 5.2+.
    $hash = hash($algo, $salt . $password, TRUE);
    do {
        $hash = hash($algo, $hash . $password, TRUE);
    } while (--$count);
    $len = strlen($hash);
    $output = $setting . _password_base64_encode($hash, $len);
    // _password_base64_encode() of a 16 byte MD5 will always be 22 characters.
    // _password_base64_encode() of a 64 byte sha512 will always be 86 characters.
    $expected = 12 + ceil(8 * $len / 6);
    return strlen($output) == $expected ? substr($output, 0, DRUPAL_HASH_LENGTH) : FALSE;
}

/**
 * Parse the log2 iteration count from a stored hash or setting string.
 */
function _password_get_count_log2($setting) {
    $itoa64 = _password_itoa64();
    return strpos($itoa64, $setting[3]);
}

/**
 * Hash a password using a secure hash.
 *
 * @param $password
 *   A plain-text password.
 * @param $count_log2
 *   Optional integer to specify the iteration count. Generally used only during
 *   mass operations where a value less than the default is needed for speed.
 *
 * @return
 *   A string containing the hashed password (and a salt), or FALSE on failure.
 */
function user_hash_password($password, $count_log2 = 0) {
    if (empty($count_log2)) {
        // Use the standard iteration count.
        $count_log2 = variable_get('password_count_log2', DRUPAL_HASH_COUNT);
    }
    return _password_crypt('sha512', $password, _password_generate_salt($count_log2));
}

/**
 * Check whether a plain text password matches a stored hashed password.
 *
 * Alternative implementations of this function may use other data in the
 * $account object, for example the uid to look up the hash in a custom table
 * or remote database.
 *
 * @param $password
 *   A plain-text password
 * @param $account
 *   A user object with at least the fields from the {users} table.
 *
 * @return
 *   TRUE or FALSE.
 */
function user_check_password($password, $account) {
    if (substr($account->pass, 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().
        $stored_hash = substr($account->pass, 1);
        $password = md5($password);
    }
    else {
        $stored_hash = $account->pass;
    }
    $type = substr($stored_hash, 0, 3);
    switch ($type) {
        case '$S$':
            // A normal Drupal 7 password using sha512.
            $hash = _password_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.
            $hash = _password_crypt('md5', $password, $stored_hash);
            break;
        default:
            return FALSE;
    }
    return $hash && $stored_hash == $hash;
}

/**
 * Check whether a user's hashed password needs to be replaced with a new hash.
 *
 * This is typically called during the login process when the plain text
 * password is available. A new hash is needed when the desired iteration count
 * has changed through a change in the variable password_count_log2 or
 * DRUPAL_HASH_COUNT or if the user's password hash was generated in an update
 * like user_update_7000().
 *
 * Alternative implementations of this function might use other criteria based
 * on the fields in $account.
 *
 * @param $account
 *   A user object with at least the fields from the {users} table.
 *
 * @return
 *   TRUE or FALSE.
 */
function user_needs_new_hash($account) {
    // Check whether this was an updated password.
    if (substr($account->pass, 0, 3) != '$S$' || strlen($account->pass) != DRUPAL_HASH_LENGTH) {
        return TRUE;
    }
    // Ensure that $count_log2 is within set bounds.
    $count_log2 = _password_enforce_log2_boundaries(variable_get('password_count_log2', DRUPAL_HASH_COUNT));
    // Check whether the iteration count used differs from the standard number.
    return _password_get_count_log2($account->pass) !== $count_log2;
}