Implementing HMAC and SHA1 encryption in swift

Question

I am relatively new to Swift and i\'m stuck encrypting using HMAC and SHA1. I Found the following answer https://stackoverflow.com/a/24411522/4188344 but i can\'t work out h

Answer 1

Using raw bytes for key and message and not encoding to utf8:

    static func getHmac_X_Sha1() -> [UInt8] {

        let msg:[UInt8] = message_uint8;
        let msgLen = message_uint8.count;
        let digestLen = Int(CC_SHA1_DIGEST_LENGTH)
        let digest = UnsafeMutablePointer.allocate(capacity: digestLen)
        let keyStr:[UInt8] = key_uint8
        let keyLen = key_uint8.count

        CCHmac(CCHmacAlgorithm(kCCHmacAlgSHA1), keyStr, keyLen, msg, msgLen, digest)


        //Build a hex string of result
        let hash_hex_string = NSMutableString()
        for i in 0.. [UInt8]? {
        let length = string.characters.count
        if length & 1 != 0 {
            return nil
        }
        var bytes = [UInt8]()
        bytes.reserveCapacity(length/2)
        var index = string.startIndex
        for _ in 0..