Working with AES encryption in IOS - ios

Question

I am getting problem while encryption.
The server is sending json data which is aes256 encrypted and then base64 encoded.
while in the ios client side i am able to get the response and decode it using base64.
The AES256 decryption works on some libraries(3rd party or wrappers aroound CommonCryptor.h) and not working in another.
When decryption is working the parsing is not working.
The following are the wrappers libraries and the respective code.
RNCryptor
(https://github.com/rnapier/RNCryptor)
NSData *decodedData = [Util decode:data];
NSData *RNDecryptedData = [RNDecryptor decryptData:decodedData withPassword:randomString error:&error];
if (error == nil) {
NSLog(#"RNDecryptedData - %#",[Util hexStringFromData:RNDecryptedData]);
response = [NSJSONSerialization JSONObjectWithData:RNDecryptedData options:NSJSONReadingMutableContainers error:&error];
NSLog(#"response - %#",response);
NSLog(#"error1 - %#",error);
} else
NSLog(#"error2 - %#",error);
I am getting following error while decryption.
EncryptedParsing[4402:70b] error2 - Error Domain=net.robnapier.RNCryptManager Code=2 "Unknown header" UserInfo=0x8c6bd60 {NSLocalizedDescription=Unknown header}
CCrypto
(https://github.com/Gurpartap/AESCrypt-ObjC)
NSData *decodedData = [Util decode:data];
NSData *CCDecryptedData = [decodedData decryptedAES256DataUsingKey:randomString error:&error];
if (error == nil) {
response = [NSJSONSerialization JSONObjectWithData:CCDecryptedData options:NSJSONReadingMutableContainers error:&error];
NSLog(#"response - %#",response);
NSLog(#"error1 - %#",error);
} else
NSLog(#"error2 - %#",error);
Here I am getting the decrypted data, but while parsing it is giving following error
EncryptedParsing[4469:70b] error1 - Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (JSON text did not start with array or object and option to allow fragments not set.) UserInfo=0x8a51520 {NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}
NSData+AES256
(http://pastie.org/426530)
NSData *decodedData = [Util decode:data];
NSData *AES256DecryptedData = [decodedData AES256DecryptWithKey:randomString];
response = [NSJSONSerialization JSONObjectWithData:AES256DecryptedData options:NSJSONReadingMutableLeaves error:&error];
NSLog(#"error - %#",error);
I am getting the decryption data, while parsing i am getting following error
EncryptedParsing[4646:70b] error - Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)" (JSON text did not start with array or object and option to allow fragments not set.) UserInfo=0x8a710c0 {NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}
Along with these I have also used CocoaSecurity (https://github.com/kelp404/CocoaSecurity)
But it is not working.
I am using NSData+Base64 (https://github.com/l4u/NSData-Base64) for base64 decoding
By the way there is no problem from server side(we tested it).
I want to know the error i am doing. Or is there any other way to achieve it

Answer 1

There is no universal standard way to encode AES encrypted data. You need agreement on both sides about how to encode the various metadata required.
RNCryptor is failing to decrypt because it expects the data to be in the RNCryptor format.
CCCrypto and AES256DecryptWithKey are probably interpreting the key differently than you intend. Neither verifies that the key you pass is correct, so you likely are getting garbage back. If that's the case, I would expect that for some messages you get garbage back, and for other messages you get nothing back, or an error.
RNCryptor has implementations in several languages if you need a cross-platform solution. If you are required to conform to a server format (which is likely not secure encryption from the looks of your code), then you'll need to provide the server code in order to determine the correct client code.

Answer 2

try to replace NSJSONReadingMutableLeaves with kNilOptions.