我应该在mcrypt_decrypt之后修剪解密的字符串吗？

时间：2009-06-30 04:40:55

标签： php encryption

我的代码类似于：

$cipher_alg = MCRYPT_RIJNDAEL_128;
$decrypted_string = mcrypt_decrypt($cipher_alg, $key, 
$encrypted_string , MCRYPT_MODE_CBC, trim(hex2bin(trim($hexiv))));

我担心在解码过程中mcrypt_decrypt会在$decrypted_string的后面或前面引入一个无偿的空格或空字符。

我应该修剪它吗？

注意：我可以运行代码并找到它。但是，由于我永远无法运行足够的样本来证明（或反驳）我的观点，我想要一些具体的理论答案，可能基于mcrypt_decrypt算法的内部工作。我问的另一个原因是我相信这会有助于其他人。

注意2：尽管有the answer below ( now deleted and only 10K users can see it)，但似乎examples here确实使用修剪来获取正确的解密字符串。

4 个答案:

答案 0 :(得分：18)

实际上，mcrypt_encrypt()和mcrypt_decrypt()以及其他加密/解密功能（例如mcrypt_generic()或mdecrypt_generic()）执行填充$data参数的长度为n * <<blocksize>>。填充字符是NUL字符（\x0或\0），而<<blocksize>>取决于使用的密码和分组密码模式。您应该查看Block cipher modes of operation和Padding (cryptography)。

以下是我机器上每种可用密码和模式的mcrypt_get_block_size()输出。显然，该函数没有考虑到诸如CFB，OFB和CTR 之类的模式不需要任何特殊措施来处理长度不是块大小的倍数的消息，因为它们都通过对明文与输出进行异或操作来工作分组密码（引自维基百科）。在您的示例中使用的CBC始终要求在加密之前填充最终块。 

cast-128
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
gost
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
rijndael-128
    cbc: 16 bytes
    cfb: 16 bytes
    ctr: 16 bytes
    ecb: 16 bytes
    ncfb: 16 bytes
    nofb: 16 bytes
    ofb: 16 bytes
    stream: not supported
twofish
    cbc: 16 bytes
    cfb: 16 bytes
    ctr: 16 bytes
    ecb: 16 bytes
    ncfb: 16 bytes
    nofb: 16 bytes
    ofb: 16 bytes
    stream: not supported
arcfour
    cbc: not supported
    cfb: not supported
    ctr: not supported
    ecb: not supported
    ncfb: not supported
    nofb: not supported
    ofb: not supported
    stream: 1 bytes
cast-256
    cbc: 16 bytes
    cfb: 16 bytes
    ctr: 16 bytes
    ecb: 16 bytes
    ncfb: 16 bytes
    nofb: 16 bytes
    ofb: 16 bytes
    stream: not supported
loki97
    cbc: 16 bytes
    cfb: 16 bytes
    ctr: 16 bytes
    ecb: 16 bytes
    ncfb: 16 bytes
    nofb: 16 bytes
    ofb: 16 bytes
    stream: not supported
rijndael-192
    cbc: 24 bytes
    cfb: 24 bytes
    ctr: 24 bytes
    ecb: 24 bytes
    ncfb: 24 bytes
    nofb: 24 bytes
    ofb: 24 bytes
    stream: not supported
saferplus
    cbc: 16 bytes
    cfb: 16 bytes
    ctr: 16 bytes
    ecb: 16 bytes
    ncfb: 16 bytes
    nofb: 16 bytes
    ofb: 16 bytes
    stream: not supported
wake
    cbc: not supported
    cfb: not supported
    ctr: not supported
    ecb: not supported
    ncfb: not supported
    nofb: not supported
    ofb: not supported
    stream: 1 bytes
blowfish-compat
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
des
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
rijndael-256
    cbc: 32 bytes
    cfb: 32 bytes
    ctr: 32 bytes
    ecb: 32 bytes
    ncfb: 32 bytes
    nofb: 32 bytes
    ofb: 32 bytes
    stream: not supported
serpent
    cbc: 16 bytes
    cfb: 16 bytes
    ctr: 16 bytes
    ecb: 16 bytes
    ncfb: 16 bytes
    nofb: 16 bytes
    ofb: 16 bytes
    stream: not supported
xtea
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
blowfish
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
enigma
    cbc: not supported
    cfb: not supported
    ctr: not supported
    ecb: not supported
    ncfb: not supported
    nofb: not supported
    ofb: not supported
    stream: 1 bytes
rc2
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported
tripledes
    cbc: 8 bytes
    cfb: 8 bytes
    ctr: 8 bytes
    ecb: 8 bytes
    ncfb: 8 bytes
    nofb: 8 bytes
    ofb: 8 bytes
    stream: not supported

因此，如果您的密码在固定长度的块上运行，则必须rtrim()解密函数的输出才能获得原始字符串：

$output = rtrim($decrypted, "\0");

答案 1 :(得分：8)

在我的TripleDES实现中，我发现解密后的字符串用\ 5或\ 6个字符填充。这不是上面提到的或在PHP.net示例中提到的\ 0或\ 4字符。要确定填充字符的ASCII值，请使用ord()功能。 ord（）适用于单个字符，因此使用str_split（）来分解字符串或使用数组表示法直接访问字符 - $ string [5]。

最终修剪结果 - trim($decrypt, "\0..\32");

最终代码结果 - 

    $key        = "encryption key";
    $encrypt    = base64_decode($encrypt);
    $iv_size    = mcrypt_get_iv_size(MCRYPT_3DES, MCRYPT_MODE_ECB);
    $iv         = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $decrypt    = mcrypt_decrypt(MCRYPT_3DES, $key, $encrypt, MCRYPT_MODE_ECB, $iv);
    $final      = trim($decrypt, "\0..\32"); // removes potential null padding

答案 2 :(得分：4)

我必须加密/解密二进制数据。不幸的是，trim可以打破二进制数据并修剪等同于空字符的合法位。

为了确保加密前后二进制数据的大小相同，Rocket Hazmat在这里发布了一个很好的答案： How can I decrypt binary data that ended with NUL characters in PHP?

要点：

// PKCS7 Padding
$blocksize = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB);
$pad = $blocksize - (strlen($data) % $blocksize);
$data .= str_repeat(chr($pad), $pad);

$encrypted = mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $key, $data, MCRYPT_MODE_ECB);


/*  Then somewhere else in your code */
$decrypted = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $encrypted, MCRYPT_MODE_ECB);

// PKCS7 Padding
$strPad = ord($decrypted[strlen($decrypted)-1]);
$newData = substr($decrypted, 0, -$strPad);

我不确定ECB与CBC的使用......

答案 3 :(得分：0)

经过24小时的研究，最终这对我有用：

function removePadding($decryptedText){
    $strPad = ord($decryptedText[strlen($decryptedText)-1]);
    $decryptedText= substr($decryptedText, 0, -$strPad);
    return $decryptedText;
}
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