<?php

/*
 * This file is part of SwiftMailer.
 * (c) 2004-2009 Chris Corbyn
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

/**
 * Handles CRAM-MD5 authentication.
 *
 * @author Chris Corbyn
 */
class Swift_Transport_Esmtp_Auth_CramMd5Authenticator implements Swift_Transport_Esmtp_Authenticator
{
    /**
     * Get the name of the AUTH mechanism this Authenticator handles.
     *
     * @return string
     */
    public function getAuthKeyword()
    {
        return 'CRAM-MD5';
    }

    /**
     * {@inheritdoc}
     */
    public function authenticate(Swift_Transport_SmtpAgent $agent, $username, $password)
    {
        try {
            $challenge = $agent->executeCommand("AUTH CRAM-MD5\r\n", [334]);
            $challenge = base64_decode(substr($challenge, 4));
            $message = base64_encode(
                $username.' '.$this->getResponse($password, $challenge)
            );
            $agent->executeCommand(sprintf("%s\r\n", $message), [235]);

            return true;
        } catch (Swift_TransportException $e) {
            $agent->executeCommand("RSET\r\n", [250]);

            throw $e;
        }
    }

    /**
     * Generate a CRAM-MD5 response from a server challenge.
     *
     * @param string $secret
     * @param string $challenge
     *
     * @return string
     */
    private function getResponse($secret, $challenge)
    {
        if (\strlen($secret) > 64) {
            $secret = pack('H32', md5($secret));
        }

        if (\strlen($secret) < 64) {
            $secret = str_pad($secret, 64, \chr(0));
        }

        $k_ipad = substr($secret, 0, 64) ^ str_repeat(\chr(0x36), 64);
        $k_opad = substr($secret, 0, 64) ^ str_repeat(\chr(0x5C), 64);

        $inner = pack('H32', md5($k_ipad.$challenge));
        $digest = md5($k_opad.$inner);

        return $digest;
    }
}
