Decrypt text iOS

Question

How to decrypt a text got as a response from the server.

I have the below parameters that was used to encrypt the string with Rijndael AES algorithm.

passPhrase = "Jxy37Kn@" saltValue = "M9!1lj5" hashAlgorithm = "SHA1" passwordIterations = 2 //Integer initVector = "@1B2c3D4e5F6g7H8" keySize = 256 //Integer

The text that I get from the server is jp9VG27FQYXh+Uvkc9meFw==

Can someone please help me to decrypt the above text in iOS by pointing to some sample code.

I use the below code

const CCAlgorithm kAlgorithm = kCCAlgorithmAES128;
const NSUInteger kAlgorithmKeySize = kCCKeySizeAES256;
const NSUInteger kAlgorithmBlockSize = kCCBlockSizeAES128;
const NSUInteger kPBKDFRounds = 2;

- (NSData *)AESKeyForPassword:(NSString *)password
                     salt:(NSData *)salt {

NSMutableData *derivedKey = [NSMutableData dataWithLength:kAlgorithmKeySize];

int result = CCKeyDerivationPBKDF(kCCPBKDF2,        // algorithm
                              password.UTF8String,  // password
                              password.length,      // passwordLength
                              salt.bytes,           // salt
                              salt.length,          // saltLen
                              kCCPRFHmacAlgSHA1,  // PRF
                              kPBKDFRounds,         // rounds
                              derivedKey.mutableBytes, // derivedKey
                              derivedKey.length);   // derivedKeyLen

// Do not log password here
NSAssert(result == kCCSuccess,
         @"Unable to create AES key for password: %d", result);

return derivedKey;
}

- (void) decryptText
{
NSData *data = [NSData dataFromBase64String:@"jp9VG27FQYXh+Uvkc9meFw=="];
NSData *iv = [@"@1B2c3D4e5F6g7H8" dataUsingEncoding:NSUTF8StringEncoding];
NSData *salt = [@"M9!1lj5" dataUsingEncoding:NSUTF8StringEncoding];

NSData *key = [self AESKeyForPassword:@"Jxy37Kn@" salt:salt];

size_t outLength;
NSMutableData *cipherData = [NSMutableData dataWithLength:data.length + kAlgorithmBlockSize];

CCCryptorStatus result = CCCrypt(kCCDecrypt, // operation
                 kAlgorithm, // Algorithm
                 kCCOptionECBMode, // options
                 key.bytes, // key
                 key.length, // keylength
                 iv.bytes,// iv
                 data.bytes, // dataIn
                 data.length, // dataInLength,
                 cipherData.mutableBytes, // dataOut
                 cipherData.length, // dataOutAvailable
                 &outLength); // dataOutMoved

if (result == kCCSuccess) {
    cipherData.length = outLength;
}
else {

}

NSString *apptStr = [[NSString alloc] initWithData:cipherData encoding:NSASCIIStringEncoding];
NSLog(@"apptStr:%@",apptStr);

}

I get this after decrypt "#Ï¢K´xÞ#É¢ç" which I believe is incorrect. What am I missing here??

Answer 1

You should not be decrypting sha1 hashes. They are designed to be one way encryptions! Rather, if you need passwords, let's say for authentication, you should have users enter password information, and then send it to the server where the server then hashes the text. It should then check the password you sent to the server (now hashed) against the version you had previously hashed before and return to your app a "success" message if it works. Since sha1 is consistently the same algorithm, it should match!

Note: if you can only receive the pass phrases, and can't change the architecture of how you are managing passwords, you could do the same sort of thing by sha1 hashing in objective-c and comparing against the password.