Decrypting a string encrypted with Rijndael Managed object in Windows .Net in Objective-C on MacOS

Question

I have some strings generated by encrypting a text string using Rijndael Managed class from System.Security.Cryptography in Windows .Net which I would like to decrypt using Objective C on MacOS. Using the CCCrypt method defined in CommCrypto.h, the decryption runs without error after I supply the key and initialization vectors used on Windows (32 and 16 bytes respectively, including some ASCII codes > 127) using code from https://www.codegrepper.com/code-examples/objectivec/objective+c+encrypt+decrypt+string as shown below, modified to set other values for IV and KEY:

NSString *const IV = @"AEE0515D0B08A4E4";
NSString *const KEY =  @"9336565521E5F082BB5929E8E033BC69";


#import "SecurityUtils.h"


@implementation SecurityUtils


+ (NSString *)encrypt:(NSString *)plainText error:(NSError **)error {
    NSMutableData *result =  [SecurityUtils doAES:[plainText dataUsingEncoding:NSUTF8StringEncoding] context: kCCEncrypt error:error];
    return [result base64EncodedStringWithOptions:0];
}


+ (NSString *)decrypt:(NSString *)encryptedBase64String error:(NSError **)error {
    NSData *dataToDecrypt = [[NSData alloc] initWithBase64EncodedString:encryptedBase64String options:0];
    NSMutableData *result = [SecurityUtils doAES:dataToDecrypt context: kCCDecrypt error:error];
    return [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding];

}

+ (NSMutableData *)doAES:(NSData *)dataIn context:(CCOperation)kCCEncrypt_or_kCCDecrypt error:(NSError **)error {
        CCCryptorStatus ccStatus   = kCCSuccess;
        size_t          cryptBytes = 0;
        NSMutableData  *dataOut    = [NSMutableData dataWithLength:dataIn.length + kCCBlockSizeBlowfish];
        NSData *key =[KEY dataUsingEncoding:NSUTF8StringEncoding];
        NSData *iv = [IV dataUsingEncoding:NSUTF8StringEncoding];

        ccStatus = CCCrypt( kCCEncrypt_or_kCCDecrypt,
                           kCCAlgorithmAES,
                           kCCOptionPKCS7Padding,
                           key.bytes,
                           key.length,
                           (iv)?nil:iv.bytes,
                           dataIn.bytes,
                           dataIn.length,
                           dataOut.mutableBytes,
                           dataOut.length,
                           &cryptBytes);

        if (ccStatus == kCCSuccess) {
            dataOut.length = cryptBytes;
        }
        else {
            if (error) {
                *error = [NSError errorWithDomain:@"kEncryptionError"
                                             code:ccStatus
                                         userInfo:nil];
            }
            dataOut = nil;
        }

        return dataOut;
}


@end

However, the output byte array does not contain the original text and cannot be converted to a string via [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding. What am I doing wrong?

Code is visible in supplied link. The only change is in definition of key and initial value. — SimonKravis, Apr 22 '21 at 08:18
That is simple text Encoding not Encryption two completely different things. — Plasma, Apr 22 '21 at 08:43

SimonKravis · Answer 1 · 2021-04-22T11:41:24.253

The problem was in the initial value setting. Replacing (iv)?nil:iv.bytes,by iv.bytes, as shown below

ccStatus = CCCrypt( kCCEncrypt_or_kCCDecrypt,
                           kCCAlgorithmAES,
                           kCCOptionPKCS7Padding,
                           key.bytes,
                           key.length,
                           iv.bytes,
                           dataIn.bytes,
                           dataIn.length,
                           dataOut.mutableBytes,
                           dataOut.length,
                           &cryptBytes);

fixed the problem.

Decrypting a string encrypted with Rijndael Managed object in Windows .Net in Objective-C on MacOS

1 Answers1