objective-c - CCCrypt解码的明文长度错误

Question

最近，我正在使用 CCCrypt 来实现一些自定义的加密算法。但是，当我使用 CCCryptorUpdate 解密密文时，输出总是比原始纯文本少 8 个字节。以下是我的代码:

+ (void) EncryptBy3DES:(NSInputStream*)strmSrc Output:(NSOutputStream*)strmDest CryptoRef:(CCCryptorRef)tdesCrypto
{   
    size_t  dataOutMoved;
    uint8_t inputBuf[BlockSize];
    uint8_t outputBuf[BlockSize];

    CCCryptorStatus cryptStatus;
    int iBytesRead = 0;

    while ( (iBytesRead = [strmSrc read:inputBuf maxLength:BlockSize]) > 0 ) 
    {
        NSLog(@"Bytes read from plain buffer: %d", iBytesRead);
        [Util FillBuffer:inputBuf Length:BlockSize Current:iBytesRead];

        cryptStatus = CCCryptorUpdate(tdesCrypto, &inputBuf, BlockSize, &outputBuf, BlockSize, &dataOutMoved);
        assert(dataOutMoved<=BlockSize && cryptStatus==noErr);
        NSLog(@"EncDataOutMoved: %ld", dataOutMoved);
        [Util FillBuffer:outputBuf Length:BlockSize Current:dataOutMoved];
        [strmDest write:outputBuf maxLength:BlockSize];
    }
}

+ (void) DecryptBy3DES:(NSInputStream*)strmSrc Output:(NSOutputStream*)strmDest CryptoRef:(CCCryptorRef)tdesCrypto
{       
    size_t  dataOutMoved;
    uint8_t inputBuf[BlockSize];
    uint8_t outputBuf[BlockSize+kCCBlockSize3DES];

    CCCryptorStatus cryptStatus;
    int iBytesRead = 0;

    while ( (iBytesRead = [strmSrc read:inputBuf maxLength:BlockSize]) > 0 ) 
    {
        NSLog(@"Bytes read from cipher buffer: %d", iBytesRead);
        cryptStatus = CCCryptorUpdate(tdesCrypto, &inputBuf, BlockSize, &outputBuf, BlockSize+kCCBlockSize3DES, &dataOutMoved);
        NSLog(@"Lengh needed: %zu", CCCryptorGetOutputLength(tdesCrypto, BlockSize, YES));
        NSLog(@"DecDataOutMoved: %ld", dataOutMoved);
        assert(dataOutMoved<=BlockSize && cryptStatus==noErr);
        [strmDest write:outputBuf maxLength:dataOutMoved];
    }
}


I encrypted 3 buffer of 4096. When decrypting them, the log shows that the size of 1st decrypted data is 4088, BUT! The missing data is actually in the begining of the 2nd decrypted data. 

2012-04-14 15:17:41.929 otest[25168:7803] Bytes read from cipher buffer: 4096
2012-04-14 15:17:41.929 otest[25168:7803] Lengh needed: 4104
2012-04-14 15:17:41.930 otest[25168:7803] DecDataOutMoved: 4088
end of 1st block:<..d71eaf27 affc4c8c b1c54afa c5434397 ebc17a49>

2012-04-14 15:17:45.291 otest[25168:7803] Bytes read from cipher buffer: 4096
2012-04-14 15:17:45.292 otest[25168:7803] Lengh needed: 4104
2012-04-14 15:17:45.293 otest[25168:7803] DecDataOutMoved: 4096
begining of 2nd block <**86b61bce b4342728** 88240a64 837327d4 0bb572a2 f5220928

请注意，86b61bce b4342728 在加密前位于第一个 block 的末尾。

我还检查了第一个 block 的开头，我确信我没有弄乱数据范围。似乎数据已解密，但要等到下一次操作才能检索到。

我想在每次加密/解密操作时获得一个完整的 block ，但我不想使用函数 CCCrypt，因为我必须将 key 和 Iv 位都传递给它。我只是想把CCCryptorRef传给它，比较简单。

休伯特

Answer 1

需要调用CCCryptFinal完成加解密.这将负责添加/删除填充。