Bitstamp - new authentication in C# - signature

Question

The new authentication of bitstamp says the following:

Signature is a HMAC-SHA256 encoded message containing: nonce, client ID and API key. The HMAC-SHA256 code must be generated using a secret key that was generated with your API key. This code must be converted to it's hexadecimal representation (64 uppercase characters).Example (Python): message = nonce + client_id + api_key signature = hmac.new(API_SECRET, msg=message, digestmod=hashlib.sha256).hexdigest().upper()

Source: link

I've got the following code to add the new signature (and other parameters):

public void AddApiAuthentication(RestRequest restRequest)
    {
        var nonce = DateTime.Now.Ticks;
        var signature = GetSignature(nonce, apiKey, apiSecret, clientId);

        restRequest.AddParameter("key", apiKey);
        restRequest.AddParameter("signature", signature);
        restRequest.AddParameter("nonce", nonce);

    }

    private string GetSignature(long nonce, string key, string secret, string clientId)
    {
        string msg = string.Format("{0}{1}{2}", nonce,
            clientId,
            key);

        return ByteArrayToString(SignHMACSHA256(secret, StrinToByteArray(msg))).ToUpper();
    }
    public static byte[] SignHMACSHA256(String key, byte[] data)
    {
        HMACSHA256 hashMaker = new HMACSHA256(Encoding.ASCII.GetBytes(key));
        return hashMaker.ComputeHash(data);
    }

    public static byte[] StrinToByteArray(string str)
    {
        byte[] bytes = new byte[str.Length * sizeof(char)];
        System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
        return bytes;
    }

    public static string ByteArrayToString(byte[] hash)
    {
        return BitConverter.ToString(hash).Replace("-", "").ToLower();
    }

And then I get this error:

{"error": "Invalid signature"}

Anyone got an idea what the problem could be? I checked my parameters a 100 times and those aren't wrong. Maybe somebody got a working piece of code (in C#) for the new authentication?

UPDATE

Abhinav was right, the StringToByteArray method was wrong (not only the typo :P) the working code is:

public static byte[] StrinToByteArray(string str)
    {
        return System.Text.Encoding.ASCII.GetBytes(str);
    }

Answer 1

You are using str.ToCharArray() in StrinToByteArray which is incorrect (correct ONLY when used on the same system). You need to use ASCII encoding or something.