Same HMAC algorithm in obj-c and swift creates different hashes - ios

Question

I have two methods that create a sha1 hash from a string. Using the same input data this algorithms create different hashes, however they should create the same hashes.
In swift (creates 617fb90f14f2eacecc333d558237bf8bb9fc85f7):
static func sha1FromMessage(message: String) -> String {
let cKey = RestUtils.API_KEY.cStringUsingEncoding(NSASCIIStringEncoding)!
let cData = message.cStringUsingEncoding(NSUTF8StringEncoding)!
var cHMAC = [CUnsignedChar](count: Int(CC_SHA1_DIGEST_LENGTH), repeatedValue: 0)
CCHmac(CCHmacAlgorithm(kCCHmacAlgSHA1), cKey, UInt(cKey.count), cData, UInt(cData.count), &cHMAC)
let output = NSMutableString(capacity: Int(CC_SHA1_DIGEST_LENGTH))
for byte in cHMAC {
output.appendFormat("%02hhx", byte)
}
return output
}
and obj-c (creates d80b816f0b46d5211b6d9487089597e181717ea6)
+(NSString *)sha1FromMessage:(NSString *)message{
const char *cKey = [API_KEY cStringUsingEncoding:NSASCIIStringEncoding];
const char *cData = [message cStringUsingEncoding:NSUTF8StringEncoding];
unsigned char cHMAC[CC_SHA1_DIGEST_LENGTH];
CCHmac(kCCHmacAlgSHA1, cKey, strlen(cKey), cData, strlen(cData), cHMAC);
NSData *HMACData = [NSData dataWithBytes:cHMAC length:sizeof(cHMAC)];
const unsigned char *buffer = (const unsigned char *)[HMACData bytes];
NSMutableString *HMAC = [NSMutableString stringWithCapacity:HMACData.length * 2];
for (int i = 0; i < HMACData.length; ++i){
[HMAC appendFormat:#"%02hhx", buffer[i]];
}
return HMAC;
}
I would like the swift method to return the same hash as the obj-c method. Any ideas where the problem is?

Answer 1

The reason is that cData created by
let cData = message.cStringUsingEncoding(NSUTF8StringEncoding)!
includes the terminating NUL-character of the message string and that is counted in
UInt(cData.count) as well. You could fix that by using UInt(strlen(cData)) instead,
as in your Objective-C code.
But a better solution is to convert the input strings
to NSData objects instead:
let cKey = RestUtils.API_KEY.dataUsingEncoding(NSASCIIStringEncoding)!
let cData = message.dataUsingEncoding(NSUTF8StringEncoding)!
var cHMAC = [CUnsignedChar](count: Int(CC_SHA1_DIGEST_LENGTH), repeatedValue: 0)
CCHmac(CCHmacAlgorithm(kCCHmacAlgSHA1), cKey.bytes, UInt(cKey.length), cData.bytes, UInt(cData.length), &cHMAC)
With this modification, Swift and Objective-C code produce the same message digest.