我应该修剪mcrypt_decrypt之后的解密字符串？ [英] Should I Trim the Decrypted String after mcrypt_decrypt?

问题描述

我有一个代码如下：

$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 mcrypt_decrypt 将在 $ decryptpted_string 的后面或前面引入一个无偿的空格或空字符。

I worry that in the process of decoding the mcrypt_decrypt will introduce a gratuitous whitespace or null characters at the back or front of the $decrypted_string.

所以应该我修剪了吗？

注意：我可以运行代码，找到这个。但是，由于我无法运行足够的样本来证明（或反驳）我的观点，我想要一些具体和理论的答案，可能基于 mcrypt_decrypt 算法的内部工作。另一个原因是我相信这会帮助别人。

Note: I could have run the code and find this out. But since I can never run enough samples to prove ( or disprove) my point, I want some concrete and theoretical answers, probably based on the inner working of the mcrypt_decrypt algorithm. Another reason I ask is that I believe this is going to help others.

注2：尽管有以下答案（现已删除，只有10K位用户可以看到它），它似乎这里的示例确实使用修剪来获得正确的解密方案

Note 2: Notwithstanding with the answer below ( now deleted and only 10K users can see it), it seems that the examples here do use trimming to get the correct decrypted string.

推荐答案

实际上 mcrypt_encrypt（） 和 mcrypt_decrypt（） 以及其他的en- / functons（如 mcrypt_generic（） 或 mdecrypt_generic（） ） do 将 $ data 参数填充到长度 n *< blocksize>> code>。填充字符是 NUL 字符（ \x0 或 \0 ），而<< blocksize>> 取决于所使用的密码和块密码模式。您应该看看阻止密码操作模式和填充（加密）。

Actually both mcrypt_encrypt() and mcrypt_decrypt() as well as the other en-/decryption functons (like mcrypt_generic() or mdecrypt_generic()) do pad the $data parameter to a length of n * <<blocksize>>. The padding character is the NUL character (\x0 or \0) whereas the <<blocksize>> depends on the cipher and the block cipher modes used. You should have a look at Block cipher modes of operation and Padding (cryptography).

以下是< a href =http://de2.php.net/manual/en/function.mcrypt-get-block-size.php =noreferrer> mcrypt_get_block_size（） 为我的机器上的每个可用的密码和模式。显然，该功能没有考虑到诸如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倍数的消息，因为它们都可以通过将输出的明文与输出进行异或的块密码（来自维基百科）。在您的示例中使用的CBC总是要求在加密之前填充最后一个块。

The following is the output of mcrypt_get_block_size() for each of the available ciphers and modes on my machine. Obviously the function does not take into account that modes such as CFB, OFB and CTR do not require any special measures to handle messages whose lengths are not multiples of the block size, since they all work by XORing the plaintext with the output of the block cipher (quote from Wikipedia). CBC which is used in your example always requires that the final block is padded before encryption.

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

所以你必须 rtrim（） 解密函数的输出获得原始字符串，如果您的密码以固定长度运行块：

Therefore you have to rtrim() the output of the decryption functions to get the original string if your cipher operates on fixed length blocks:

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

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