In my project I got to implement AES 128 CBC Encryption. I am using Category and is based on NSData. This is my encryption code :
- (NSData*)AES128Decrypt
{
char ivPtr[kCCKeySizeAES128 + 1];
bzero(ivPtr, sizeof(ivPtr));
// fetch iv data
[iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];
// 'key' should be 32 bytes for AES256, will be null-padded otherwise
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]; // dataLength = 19
//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 numBytesDecrypted = 0;
CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, 0,
keyPtr, kCCKeySizeAES128,
ivPtr,
[self bytes], dataLength,
buffer, bufferSize,
&numBytesDecrypted); // buffer = 0 & numBytesDecrypted = 0
if (cryptStatus == kCCSuccess)
{
//the returned NSData takes ownership of the buffer and will free it on deallocation
return [NSData dataWithBytes:buffer length:numBytesDecrypted] ; // returns 0
}
free(buffer); //free the buffer;
return nil;
}
And this is how I am calling it from my view class :
- (void) testActuallyEncrypting :(NSString*) hexString {
NSLog(@"String to Encrypt : %@", hexString); // prints test12
@try {
//Convert NSString to NSData
NSData *data = [self dataFromHexString:hexString]; // [hexString dataUsingEncoding:NSUTF8StringEncoding]; //
// // Prepare the NSDAta obj to store the encrypted pswd
NSData *encryptedData = [NSData dataWithBytes:[data bytes] length:[data length]]; // 6bytes
NSData *decryptedData = [encryptedData AES128Decrypt]; // 0bytes
NSString *decryptedString = [NSString stringWithUTF8String:[decryptedData bytes]]; // NULL Exception
NSLog(@"Decrypted String : %@", decryptedString);
decryptedString = [self addPaddingToString:decryptedString];
decryptedData = [NSData dataWithBytes:[decryptedString UTF8String] length:[[decryptedString dataUsingEncoding:NSUTF8StringEncoding] length]];
encryptedData = [decryptedData AES128Encrypt];
if (encryptedData!=nil)
{
NSString *encryptedHexString = [self hexStringFromData:encryptedData];
NSLog(@"Encrypted HexString : %@",encryptedHexString);
}
}@catch (NSException *ex) {
NSLog(@"Exception : %@", ex);
}
}
I am passing "test12" string to be encrypted. On calling AES128Decrypt, decryptedData is 0, due to which the next line decryptedString throws Null exception - Exception : *** +[NSString stringWithUTF8String:]: NULL cString.
Can anyone help me know why the decryptedData is null. Where am I going wrong in the AES128Decrypt method ?
Please help me. I am stuck on this from last 2 days. Searched on this a lot on internet, but couldn't get any solution to get thru it. Any help is highly appreciated. Thanks.
UPDATE :- Added @Zaph's method in my class and am calling it.
NSLog(@"String to Encrypt : %@", hexString);
NSString *iv = @"fedcba9876543210";
NSString *key = @"0123456789abcdef";
// Convert str to encrypt, iv & key from NSString to NSData
NSData *dataIn = [hexString dataUsingEncoding:NSUTF8StringEncoding];
NSData *ivData = [iv dataUsingEncoding:NSUTF8StringEncoding];
NSData *symKey = [key dataUsingEncoding:NSUTF8StringEncoding];
NSError *error;
NSData *result = [LoginViewController doCipher:dataIn iv:ivData key:symKey context:kCCEncrypt error:&error]; // result = 16bytes
if (result != nil) {
// Convert result to satring
NSString *resultStr = [[NSString alloc] initWithData:result encoding:NSUTF8StringEncoding];
NSLog(@"Encrypted Str = %@", resultStr ); // Encrypted Str = (null) ????
Why the converted string is null ? Any help please. Thanks
