Objective-C sample code for HMAC-SHA1

Here's how you generate an HMAC using SHA-256:

NSString *key;
NSString *data;

const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [data cStringUsingEncoding:NSASCIIStringEncoding];

unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH];

CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC);

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

NSString *hash = [HMAC base64Encoding];

I'm not aware of an HOTP library, but the algorithm was quite simple, if I recall correctly.

Out of interest, why do you create (unsigned char cHMAC) and then convert into (NSData) and then convert it into (NSMutableString) and then convert finally into (HexString)?

You could do this in a quicker way by cutting the middleman (i.e. without NSData and NSMutableString altogether, quicker and better performance), also changing (unsigned char) into (uint8_t []), after all they are all hex-arrays anyway!, below:

-(NSString *)hmac:(NSString *)plaintext withKey:(NSString *)key
{
const char *cKey  = [key cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [plaintext cStringUsingEncoding:NSASCIIStringEncoding];

uint8_t cHMAC[CC_SHA1_DIGEST_LENGTH];

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

NSString *Hash1 = @"";
for (int i=0; i< CC_SHA1_DIGEST_LENGTH; i++)
{
    Hash1 = [Hash1 stringByAppendingString:[NSString stringWithFormat:@"%02X", cHMAC[i]]];
}
return Hash1;
}

I hope this helps,

Regards

Heider Sati

Have you seen Jens Alfke's new MyCrypto classes?

He has some sample code on his blog.