AES Encryption in IOS to Decryption in JAVA

Question

I am having trouble decrypting an mp3 file in JAVA which I encrypted using IOS. Below is the code used for encrypting the file in IOS:

- (NSData *)AES256EncryptWithKey:(NSData *) audioData: (NSString *)key{
// 'key' should be 32 bytes for AES256, will be null-padded otherwise
char keyPtr[kCCKeySizeAES256 + 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 = [audioData 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, kCCKeySizeAES256,
                                      NULL /* initialization vector (optional) */,
                                      [audioData 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 below is the code I am using to decrypt the file in JAVA, I call this function to decrypt:

    private static final byte[] SALT = {
        (byte) 0xA9, (byte) 0x9B, (byte) 0xC8, (byte) 0x32,
        (byte) 0x56, (byte) 0x35, (byte) 0xE3, (byte) 0x03
};
private static final int ITERATION_COUNT = 65536;
private static final int KEY_LENGTH = 256;
public static void encryptOrDecrypt(String key, byte[] is, OutputStream os) throws Throwable {
    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
    KeySpec spec = new PBEKeySpec(key.toCharArray(), SALT, ITERATION_COUNT, KEY_LENGTH);
    SecretKey tmp = factory.generateSecret(spec);
    SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
    Cipher ecipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
    byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
    IvParameterSpec ivspec = new IvParameterSpec(iv);
    ecipher.init(Cipher.DECRYPT_MODE, secret, ivspec);

    byte[] encrypted = ecipher.doFinal(is);
    os.write(encrypted);
    os.close();

}

Also here is the key I am using across both:

"3STI5F2F41608581SO3D8UN346D2E81009THEC7E220RAD9F9C29BPY738956BBE"

When I run the java application I get this error:

javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)....

Any help would be greatly appreciated.

Thanks Michael

Answer 1

Short Answer

Your Java code is using PBKDF2 to transform your key, and it looks like your Obj-C code is not (though you haven't given enough code for us to be sure). So the key is different, which is why your decryption is not working.

Unsolicited Free Advice

It looks like you're just cutting and pasting code from different places without really understanding it. If you want to use crypto, you need to understand what you're doing or you can really mess things up (even if they seem to be working). If you don't know the difference between a password and a key, or what PBKDF2 is and when to use it, then you need to do some basic research.