AES CBC 中的 CCCrypt 解密即使没有 IV 也可以工作 [英] CCCrypt decrypting in AES CBC works even without IV
问题描述
我有一个令人困惑的问题，在解密使用 CCCrypt 的 AES-CBC 模式和随机 16 字节 IV 加密的文件时，无论我传递用于加密的相同正确 IV 还是根本不传递，都会产生完全相同的输出.
I have a confusing problem, where decrypting a file which was encrypted using CCCrypt's AES-CBC mode with a randomized, 16byte IV produces the exact same output whether I pass in the same correct IV used for encryption or none at all.
我的期望:使用 NULL IV 进行解密不应导致正确的解密.我观察到:使用 NULL IV 的结果与用于加密的 IV 的结果相同.
What I expect: using a NULL IV for decrypting should not result in a correct decryption. What I observe: using a NULL IV results in the same result as with the IV used for encryption.
为了完整起见，下面是重要的代码片段，iv 作为 16 字节的安全随机 NSData 传入.
Below for sake of completeness, here's the important code snippets, iv is passed in as 16-byte securely randomized NSData.
我在这里不明白什么?CCCrypt 是否以某种方式自行从加密数据中找出 IV?我在文档中找不到任何相关内容.
What am I not understanding here? Is CCCrypt somehow figuring out the IV from the encrypted data by itself? I couldn't find anything around that in the docs.
- (NSData *)encryptedDataForData:(NSData *)rawData
withKey:(NSData *)key
iv:(NSData *)iv
error:(NSError __autoreleasing**)error
{
size_t outLength;
NSMutableData *cipherData = [NSMutableData dataWithLength:rawData.length + kAlgorithmBlockSize];
CCCryptorStatus result = CCCrypt(kCCEncrypt,
kCCAlgorithmAES128,
kCCOptionPKCS7Padding | kCCModeCBC,
key.bytes,
key.length,
iv.bytes,
rawData.bytes,
rawData.length,
cipherData.mutableBytes,
cipherData.length,
&outLength);
if (result == kCCSuccess) {
cipherData.length = outLength;
return cipherData;
} else {
return nil;
}
}
- (NSData *)decryptedDataForData:(NSData *)encryptedData withKey:(NSData *)key error:(NSError __autoreleasing**)error
{
size_t outLength;
NSMutableData *decryptedData = [NSMutableData dataWithLength:encryptedData.length];
// this line is just to illustrate how setting the exact same iv here - if this one
// was used for encryption - results in same output as when passing iv = NULL
NSData *iv = [Cryptor dataForHex:@"724a7fc0 0d8ac9d5 f09ff4c1 64d2d1bb"];
CCCryptorStatus result = CCCrypt(kCCDecrypt,
kCCAlgorithmAES128,
kCCOptionPKCS7Padding | kCCModeCBC,
key.bytes,
key.length,
iv.bytes, // iv OR NULL --> same result o_O
encryptedData.bytes,
encryptedData.length,
decryptedData.mutableBytes,
decryptedData.length,
&outLength);
if (result == kCCSuccess) {
decryptedData.length = outLength;
return decryptedData;
} else {
return nil;
}
}
为了详细说明这一点，无论我使用哪种 IV 进行解密(尝试了几个不同的随机 IV)，我总是会逐字节地得到相同的结果.即使我只解密了加密文件中间某处的部分加密文件.
To elaborate on this, no matter which IV I use for decryption (tried out a couple of different randomized IV's) I always do get byte for byte the identical results. Even when I decrypt only some partial chunk of the encrypted file somewhere from the middle of the encrypted file.
这可能与我正在加密/解密的实际数据(mp3 文件)有关吗?
Is this maybe related to the actual data I am en/decrypting (mp3 files)?
当我只是将一些实际加密文件的任意块传递给解密器时，它不应该要求该块数据(我没有明确提供作为 IV)之前的块来进行正确的解密吗?我个人能想到的唯一解释是 CCCrypt 总是使用前 16 字节作为 IV，并且不解密这些，而是将它们丢弃在输出中.
When I just pass some arbitrary chunk of the actual encrypted file to the decryptor, shouldn't it require the block right before that chunk of data (which I do not provide explicitly as the IV) to do the proper decryption? The only explanation I could think of here personally is that CCCrypt just always uses the first 16-bytes as the IV and does not decrypt those but drops them in the output.
编辑 2:
en/decryption的输出，显示输入和输出数据的前两个块，key和iv:
Output of en/decryption, showing the first two blocks of in and output data, the key and the iv:
# encryption
data <4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
iv <724a7fc0 0d8ac9d5 f09ff4c1 64d2d1bb>
key <78656a1a 337fddd6 fa52e34d 9156d187>
encrypted <cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce>
# decryption with correct IV
data <cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce>
iv <724a7fc0 0d8ac9d5 f09ff4c1 64d2d1bb>
key <78656a1a 337fddd6 fa52e34d 9156d187>
decrypted <4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
# decryption with zero IV
data <cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce>
iv <00000000 00000000 00000000 00000000>
key <78656a1a 337fddd6 fa52e34d 9156d187>
decrypted <4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
# decryption with different IV
data <cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce>
iv <12345678 9abcdef1 23456789 abcdef12>
key <78656a1a 337fddd6 fa52e34d 9156d187>
decrypted <4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
编辑 3:
-dataForHex:的代码是:
+ (NSData *)dataForHex:(NSString *)hex
{
NSString *hexNoSpaces = [[[hex stringByReplacingOccurrencesOfString:@" " withString:@""]
stringByReplacingOccurrencesOfString:@"<" withString:@""]
stringByReplacingOccurrencesOfString:@">" withString:@""];
NSMutableData *data = [[NSMutableData alloc] init];
unsigned char whole_byte = 0;
char byte_chars[3] = {' ',' ',' '};
for (NSUInteger i = 0; i < [hexNoSpaces length] / 2; i++) {
byte_chars[0] = (unsigned char) [hexNoSpaces characterAtIndex:(NSUInteger) (i * 2)];
byte_chars[1] = (unsigned char) [hexNoSpaces characterAtIndex:(NSUInteger) (i * 2 + 1)];
whole_byte = (unsigned char)strtol(byte_chars, NULL, 16);
[data appendBytes:&whole_byte length:1];
}
return data;
}
推荐答案
用于格式化注释.
使用 iv:
clear data: <4cd9b050 30c04bf9 2a0cb024 19010a31>
iv data: <724a7fc0 0d8ac9d5 f09ff4c1 64d2d1bb>
key data: <78656a1a 337fddd6 fa52e34d 9156d187>
crypt data: <d2c2efee 54e43781 549eec03 9db688e1 7c4248e7 e2ac1d80 7105ffae 4043ffb3>
decrypt data: <4cd9b050 30c04bf9 2a0cb024 19010a31>
iv 为 0:
clear data: <4cd9b050 30c04bf9 2a0cb024 19010a31>
iv data: <00000000 00000000 00000000 00000000>
key data: <78656a1a 337fddd6 fa52e34d 9156d187>
crypt data: <cf85cdbe 10a87309 a6fb4c4e ce640619 6be7b155 9db3f066 97e461e7 ced7960f>
decrypt data: <4cd9b050 30c04bf9 2a0cb024 19010a31>
很明显，在 OP 代码中没有使用 iv.
It is clear that the iv is not being used in the OP code.
以上代码:
CCCryptorStatus ccStatus = kCCSuccess;
size_t cryptBytes = 0;
NSMutableData *dataOut = [NSMutableData dataWithLength:dataIn.length + kCCBlockSizeAES128];
ccStatus = CCCrypt( encryptOrDecrypt, // kCCEncrypt or kCCDecrypt
kCCAlgorithmAES128,
kCCOptionPKCS7Padding,
key.bytes,
kCCKeySizeAES128,
iv.bytes,
dataIn.bytes,
dataIn.length,
dataOut.mutableBytes,
dataOut.length,
&cryptBytes);
dataOut.length = cryptBytes;
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