<?php

require_once dirname(__FILE__).'/openpgp.php';
require_once 'Crypt/AES.php';
require_once 'Crypt/TripleDES.php';

class OpenPGP_Crypt_AES_TripleDES {
  public static function decryptSymmetric($pass, $m) {
    $epacket = self::getEncryptedData($m);

    foreach($m as $p) {
      if($p instanceof OpenPGP_SymmetricSessionKeyPacket) {
        if(strlen($p->encrypted_data) > 0) {
          list($cipher, $key_bytes, $key_block_bytes) = self::getCipher($p->symmetric_algorithm);
          if(!$cipher) continue;
          $cipher->setKey($p->s2k->make_key($pass, $key_bytes));

          $padAmount = $key_block_bytes - (strlen($p->encrypted_data) % $key_block_bytes);
          $data = substr($cipher->decrypt($p->encrypted_data . str_repeat("\0", $padAmount)), 0, strlen($p->encrypted_data));
          $decrypted = self::decryptPacket($epacket, ord($data{0}), substr($data, 1));
        } else {
          list($cipher, $key_bytes, $key_block_bytes) = self::getCipher($p->symmetric_algorithm);
          $decrypted = self::decryptPacket($epacket, $p->symmetric_algorithm, $p->s2k->make_key($pass, $key_bytes));
        }

        if($decrypted) return $decrypted;
      }
    }

    return NULL; /* If we get here, we failed */
  }

  public static function decryptPacket($epacket, $symmetric_algorithm, $key) {
    list($cipher, $key_bytes, $key_block_bytes) = self::getCipher($symmetric_algorithm);
    if(!$cipher) return NULL;
    $cipher->setKey($key);

    $padAmount = $key_block_bytes - (strlen($epacket->data) % $key_block_bytes);

    if($epacket instanceof OpenPGP_IntegrityProtectedDataPacket) {
       $data = substr($cipher->decrypt($epacket->data . str_repeat("\0", $padAmount)), 0, strlen($epacket->data));
       $prefix = substr($data, 0, $key_block_bytes + 2);
       $mdc = substr(substr($data, -22, 22), 2);
       $data = substr($data, $key_block_bytes + 2, -22);

       $mkMDC = hash("sha1", $prefix . $data . "\xD3\x14", true);
       if($mkMDC !== $mdc) return false;

       try {
         $msg = OpenPGP_Message::parse($data);
       } catch (Exception $ex) { $msg = NULL; }
       if($msg) return $msg; /* Otherwise keep trying */
    } else {
       // No MDC mean decrypt with resync
       $iv = substr($epacket->data, 2, $key_block_bytes);
       $edata = substr($epacket->data, $key_block_bytes + 2);

       $cipher->setIV($iv);
       $data = substr($cipher->decrypt($edata . str_repeat("\0", $padAmount)), 0, strlen($edata));

       try {
         $msg = OpenPGP_Message::parse($data);
       } catch (Exception $ex) { $msg = NULL; }
       if($msg) return $msg; /* Otherwise keep trying */
    }

    return NULL; /* Failed */
  }

  public static function getCipher($algo) {
    switch($algo) {
      case 2:
        $cipher = new Crypt_TripleDES(CRYPT_DES_MODE_CFB);
        $key_bytes = 24;
        $key_block_bytes = 8;
        break;
      case 7:
        $cipher = new Crypt_AES(CRYPT_AES_MODE_CFB);
        $cipher->setKeyLength(128);
        break;
      case 8:
        $cipher = new Crypt_AES(CRYPT_AES_MODE_CFB);
        $cipher->setKeyLength(192);
        break;
      case 9:
        $cipher = new Crypt_AES(CRYPT_AES_MODE_CFB);
        $cipher->setKeyLength(256);
        break;
      default:
        $cipher = NULL;
    }
    if(!$cipher) return array(NULL, NULL, NULL); // Unsupported cipher
    if(!isset($key_bytes)) $key_bytes = $cipher->key_size;
    if(!isset($key_block_bytes)) $key_block_bytes = $cipher->block_size;
    return array($cipher, $key_bytes, $key_block_bytes);
  }

  public static function getEncryptedData($m) {
    foreach($m as $p) {
      if($p instanceof OpenPGP_EncryptedDataPacket) return $p;
    }
    throw new Exception("Can only decrypt EncryptedDataPacket");
  }
}