HMAC SHA1 with NSData input Objective-C

Question

I need to hash a NSData input with HMAC-SHA1. I used this code:

- (NSString *)HMACSHA1:(NSData *)data {
    NSParameterAssert(data);

    const char *cKey = [@"SampleSecretKey012345678" cStringUsingEncoding:NSUTF8StringEncoding];
    const void *cData = [data bytes];

    unsigned char cHMAC[CC_SHA1_DIGEST_LENGTH];

    CCHmac(kCCHmacAlgSHA1, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

    NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)];\

    /* Returns hexadecimal string of NSData. Empty string if data is empty. */

    const unsigned char *dataBuffer = (const unsigned char *)[HMAC bytes];

    if (!dataBuffer) {
        return [NSString string];
    }

    NSUInteger dataLength = [HMAC length];
    NSMutableString *hexString = [NSMutableString stringWithCapacity:(dataLength * 2)];

    for (int i = 0; i < dataLength; ++i) {
        [hexString appendFormat:@"%02x", (unsigned int)dataBuffer[i]];
    }

    return [NSString stringWithString:hexString];
}

but the hex string output is always wrong (checked from server). I think the problem is this line:

const void *cData = [data bytes];

because if convert data (sample "test" string) in the same way as key:

const void *cData = [@"test" cStringUsingEncoding:NSUTF8StringEncoding];

then check the result using this page: HMAC crypt, the result is matched.

If I hash a NSString then I can use cStringUsingEncoding: but I can't figure out convert NSData to const void*. Anyone can help me? Thanks!

Answer 1

Common Crypto supports HMAC with SHA1, MD5, SHA256, SHA384, SHA512 and SHA224.

Here is an example implementation that is a little simpler, not sure if it resolves yourproblem since no input/desired output was supplied:

- (NSString *)HMACSHA1:(NSData *)data {
    NSParameterAssert(data);

    NSData *keyData = [@"SampleSecretKey012345678" dataUsingEncoding:NSUTF8StringEncoding];
    NSMutableData *hMacOut = [NSMutableData dataWithLength:CC_SHA1_DIGEST_LENGTH];

    CCHmac(kCCHmacAlgSHA1,
           keyData.bytes, keyData.length,
           data.bytes,    data.length,
           hMacOut.mutableBytes);

    /* Returns hexadecimal string of NSData. Empty string if data is empty. */
    NSString *hexString = @"";
    if (data) {
        uint8_t *dataPointer = (uint8_t *)(hMacOut.bytes);
        for (int i = 0; i < CC_SHA1_DIGEST_LENGTH; i++) {
            hexString = [hexString stringByAppendingFormat:@"%02x", dataPointer[i]];
        }
    }

    return hexString;
}