CCCrypt解密在AES CBC即使没有IV [英] CCCrypt decrypting in AES CBC works even without IV
问题描述
我有一个混乱的问题，解密一个文件，使用CCCrypt的AES-CBC模式加密与一个随机，16byte IV产生完全相同的输出，无论我通过相同的正确的IV用于加密或根本没有。 / p>
我期望：使用NULL IV解密不应导致正确的解密。
我观察到：使用NULL IV结果与用于加密的IV结果相同。
为了完整起见，下面是重要的代码snippets， iv 以16字节安全随机NSData的形式传递。
我不明白这里？是CCCrypt以某种方式从加密的数据自己计算出IV吗？我在文档中找不到任何东西。
- （NSData *）encryptedDataForData：（NSData *）rawData
withKey：（NSData *）key
iv：（NSData *）iv
错误：（NSError __autoreleasing **）错误
{
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 *）密钥错误：（NSError __autoreleasing **）错误
（NSData *）密钥错误（NSError __autoreleasing **）错误
- （NSData *）decryptedDataForData： {
size_t outLength;
NSMutableData * decryptptedData = [NSMutableData dataWithLength：encryptedData.length];
//这行只是为了说明如何设置完全相同的iv - 如果这一个
//用于加密 - 产生与传递时相同的输出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 - >相同的结果o_O
encryptedData.bytes，
encryptedData.length，
decryptptedData.mutableBytes，
decryptptedData.length，
& outLength）;
if（result == kCCSuccess）{
decryptptedData.length = outLength;
return decryptedData;
} else {
return nil;
}
}
EDIT： p>
要详细说明，无论我使用哪个IV来解密（尝试了几个不同的随机IV），我总是得到字节的字节相同的结果。即使我只从加密文件的中间某处解密加密文件的一些部分块。
这可能与我正在/解密的实际数据有关mp3文件）？
当我只是将一些实际加密文件的任意块传递给解密器时，应该不需要块的数据我不明确地提供IV）做正确的解密？我可以在这里个人想到的唯一解释是，CCCrypt只是总是使用第一个16字节作为IV，不解密，但它们在输出中丢弃它们。
编辑2：
输出en /解密，显示输入和输出数据的前两个块，键和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>
＃正确的解密IV
data< cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce&
iv< 724a7fc0 0d8ac9d5 f09ff4c1 64d2d1bb>
key< 78656a1a 337fddd6 fa52e34d 9156d187>
解密< 4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
＃用零解密IV
data< cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce>
iv< 00000000 00000000 00000000 00000000>
key< 78656a1a 337fddd6 fa52e34d 9156d187>
解密< 4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
＃用不同IV进行解密
数据< cf85cdbe 10a87309 a6fb4c4e ce640619 8f445b70 3738018a e78291a7 b4ea26ce>
iv< 12345678 9abcdef1 23456789 abcdef12>
key< 78656a1a 337fddd6 fa52e34d 9156d187>
解密< 4cd9b050 30c04bf9 2a0cb024 19010a31 400c2261 0069196a d77bcae6 9799ae26>
编辑3：
-dataForHex：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] = {'\0'，'\0'，'\0'};
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];
}
返回数据;
}
用于格式化注释。 / p>
使用iv：
清除资料：< 4cd9b050 30c04bf9 2a0cb024 19010a31> ;
iv data：< 724a7fc0 0d8ac9d5 f09ff4c1 64d2d1bb>
键数据：< 78656a1a 337fddd6 fa52e34d 9156d187>
crypt data：< d2c2efee 54e43781 549eec03 9db688e1 7c4248e7 e2ac1d80 7105ffae 4043ffb3>
解密数据：< 4cd9b050 30c04bf9 2a0cb024 19010a31>
iv为0：
清除数据：< 4cd9b050 30c04bf9 2a0cb024 19010a31>
iv data：< 00000000 00000000 00000000 00000000>
键数据：< 78656a1a 337fddd6 fa52e34d 9156d187>
crypt data：< cf85cdbe 10a87309 a6fb4c4e ce640619 6be7b155 9db3f066 97e461e7 ced7960f>
解密数据：< 4cd9b050 30c04bf9 2a0cb024 19010a31>
很明显，iv并未在OP代码中使用。
上述代码：
CCCryptorStatus ccStatus = kCCSuccess;
size_t cryptBytes = 0;
NSMutableData * dataOut = [NSMutableData dataWithLength：dataIn.length + kCCBlockSizeAES128];
ccStatus = CCCrypt（encryptOrDecrypt，// kCCEncrypt或kCCDecrypt
kCCAlgorithmAES128，
kCCOptionPKCS7Padding，
key.bytes，
kCCKeySizeAES128，
iv .bytes，
dataIn.bytes，
dataIn.length，
dataOut.mutableBytes，
dataOut.length，
& cryptBytes）;
dataOut.length = cryptBytes;
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.
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.
Below for sake of completeness, here's the important code snippets, iv is passed in as 16-byte securely randomized NSData.
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;
}
}
EDIT:
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.
Is this maybe related to the actual data I am en/decrypting (mp3 files)?
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.
EDIT 2:
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>
EDIT 3:
The code for -dataForHex: is:
+ (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] = {'\0','\0','\0'};
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;
}
Used for formatting comment.
With 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>
With iv of 0's:
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>
It is clear that the iv is not being used in the OP code.
Code for above:
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;
这篇关于CCCrypt解密在AES CBC即使没有IV的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
