/// <summary>Signs a message with HMAC-SHA512-256.</summary>
/// <param name="message">The message.</param>
/// <param name="key">The 32 byte key.</param>
/// <returns>32 byte authentication code.</returns>
/// <exception cref="KeyOutOfRangeException"></exception>
public static byte[] Sign(byte[] message, byte[] key)
{
//validate the length of the key
if (key == null || key.Length != KEY_BYTES)
{
throw new KeyOutOfRangeException("key", (key == null) ? 0 : key.Length,
string.Format("key must be {0} bytes in length.", KEY_BYTES));
}
var buffer = new byte[BYTES];
SodiumLibrary.crypto_auth(buffer, message, message.Length, key);
return(buffer);
}