静态方法：SHA256哈希算法

 public static string SHA256Hash(string value)
        {
            if (string.IsNullOrEmpty(value)) return string.Empty;
            using (SHA256 sha256Hash = SHA256.Create())
            {
                // Convert the input string to a byte array and compute the hash.
                byte[] data = sha256Hash.ComputeHash(Encoding.UTF8.GetBytes(value));

                // Create a new Stringbuilder to collect the bytes
                // and create a string.
                StringBuilder sBuilder = new StringBuilder();

                // Loop through each byte of the hashed data 
                // and format each one as a hexadecimal string.
                for (int i = 0; i < data.Length; i++)
                {
                    sBuilder.Append(data[i].ToString("x2"));
                }
                // Return the hexadecimal string.
                return sBuilder.ToString();
            }
        }

        public static bool VerifySHA256Hash(string input, string hash)
        {
            if (string.IsNullOrEmpty(input)) return false;
            if (string.IsNullOrEmpty(hash)) return false;
            // Hash the input.
            string hashOfInput = SHA256Hash(input);

            // Create a StringComparer an compare the hashes.
            StringComparer comparer = StringComparer.OrdinalIgnoreCase;

            if (0 == comparer.Compare(hashOfInput, hash))
            {
                return true;
            }
            else
            {
                return false;
            }
            //return 0 == comparer.Compare(hashOfInput, hash) ? true : false;
        }