Help needed with AES between Java and Objective-C (iPhone)....
- by Simon Lee
I am encrypting a string in objective-c and also encrypting the same string in Java using AES and am seeing some strange issues. The first part of the result matches up to a certain point but then it is different, hence when i go to decode the result from Java onto the iPhone it cant decrypt it.
I am using a source string of "Now then and what is this nonsense all about. Do you know?"
Using a key of "1234567890123456"
The objective-c code to encrypt is the following: NOTE: it is a NSData category so assume that the method is called on an NSData object so 'self' contains the byte data to encrypt.
- (NSData *)AESEncryptWithKey:(NSString *)key {
char keyPtr[kCCKeySizeAES128+1]; // room for terminator (unused)
bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
// fetch key data
[key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];
NSUInteger dataLength = [self length];
//See the doc: For block ciphers, the output size will always be less than or
//equal to the input size plus the size of one block.
//That's why we need to add the size of one block here
size_t bufferSize = dataLength + kCCBlockSizeAES128;
void *buffer = malloc(bufferSize);
size_t numBytesEncrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
keyPtr, kCCKeySizeAES128,
NULL /* initialization vector (optional) */,
[self bytes], dataLength, /* input */
buffer, bufferSize, /* output */
&numBytesEncrypted);
if (cryptStatus == kCCSuccess) {
//the returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
}
free(buffer); //free the buffer;
return nil;
}
And the java encryption code is...
public byte[] encryptData(byte[] data, String key) {
byte[] encrypted = null;
Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
byte[] keyBytes = key.getBytes();
SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");
try {
Cipher cipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC");
cipher.init(Cipher.ENCRYPT_MODE, keySpec);
encrypted = new byte[cipher.getOutputSize(data.length)];
int ctLength = cipher.update(data, 0, data.length, encrypted, 0);
ctLength += cipher.doFinal(encrypted, ctLength);
} catch (Exception e) {
logger.log(Level.SEVERE, e.getMessage());
} finally {
return encrypted;
}
}
The hex output of the objective-c code is -
7a68ea36 8288c73d f7c45d8d 22432577 9693920a 4fae38b2 2e4bdcef 9aeb8afe 69394f3e 1eb62fa7 74da2b5c 8d7b3c89 a295d306 f1f90349 6899ac34 63a6efa0
and the java output is -
7a68ea36 8288c73d f7c45d8d 22432577 e66b32f9 772b6679 d7c0cb69 037b8740 883f8211 748229f4 723984beb 50b5aea1 f17594c9 fad2d05e e0926805 572156d
As you can see everything is fine up to -
7a68ea36 8288c73d f7c45d8d 22432577
I am guessing I have some of the settings different but can't work out what, I tried changing between ECB and CBC on the java side and it had no effect.
Can anyone help!? please....
