C# HMACSHA256.Clear方法代码示例

 // Computes a keyed hash for a source file, creates a target file with the keyed hash
 // prepended to the contents of the source file, then decrypts the file and compares
 // the source and the decrypted files.
 public static void EncodeFile(byte[] key, String sourceFile, String destFile)
 {
     // Initialize the keyed hash object.
     HMACSHA256 myhmacsha256 = new HMACSHA256(key);
     FileStream inStream = new FileStream(sourceFile, FileMode.Open);
     FileStream outStream = new FileStream(destFile, FileMode.Create);
     // Compute the hash of the input file.
     byte[] hashValue = myhmacsha256.ComputeHash(inStream);
     // Reset inStream to the beginning of the file.
     inStream.Position = 0;
     // Write the computed hash value to the output file.
     outStream.Write(hashValue, 0, hashValue.Length);
     // Copy the contents of the sourceFile to the destFile.
     int bytesRead;
     // read 1K at a time
     byte[] buffer = new byte[1024];
     do
     {
         // Read from the wrapping CryptoStream.
         bytesRead = inStream.Read(buffer, 0, 1024);
         outStream.Write(buffer, 0, bytesRead);
     } while (bytesRead > 0);
     myhmacsha256.Clear();
     // Close the streams
     inStream.Close();
     outStream.Close();
     return;
 }

        public static string GenerateHMACSHA256Hash(string Password, string QueueId, string UrlToHash)
        {
            ValidateInput(QueueId, "QueueId");
            ValidateInput(Password, "Password");
            ValidateInput(UrlToHash, "UrlToHash");

            // Create a random key using a random number generator. This would be the
            //  secret key shared by sender and receiver.
            byte[] secretkey = new Byte[64];
            Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes(Password, Encoding.UTF8.GetBytes(QueueId));
            secretkey = deriveBytes.GetBytes(64);

            // Initialize the keyed hash object.
            HMACSHA256 myhmacsha256 = new HMACSHA256(secretkey);
            byte[] byteStringToHash = Encoding.UTF8.GetBytes(UrlToHash);
            byte[] hashValue = myhmacsha256.ComputeHash(byteStringToHash);
            myhmacsha256.Clear();

            string hashStr = Encoding.ASCII.GetString(hashValue);
            string UrlEncodeHashString = HttpUtility.UrlEncode(hashStr);
            //not all special characters like = and / are encoded on first UrlEncoding
            //UrlEncoding once more fixes the problem......
            UrlEncodeHashString = HttpUtility.UrlEncode(UrlEncodeHashString);

            return UrlEncodeHashString;
        }

 // Hashing a value using HMAC-256
 private void HMACHash()
 {
     ASCIIEncoding encode = new ASCIIEncoding();
     HMACSHA256 hmac256 = new HMACSHA256(key);
     byte[] uniqueAsByte = encode.GetBytes(unique);
     byte[] hashedUnique = hmac256.ComputeHash(uniqueAsByte);
     unique = null;
     unique = ByteToString(hashedUnique);
     hmac256.Clear();
 }

        /// <summary>
        ///     站内应用使用SignedRequest获取AccessToken
        /// </summary>
        /// <param name="signedRequest">SignedRequest</param>
        /// <returns></returns>
        public AccessToken GetAccessTokenBySignedRequest(string signedRequest) {
            var parameters = signedRequest.Split('.');
            if (parameters.Length < 2) {
                throw new Exception("SignedRequest格式错误。");
            }
            var encodedSig = parameters[0];
            var payload = parameters[1];
            var sha256 = new HMACSHA256(Encoding.UTF8.GetBytes(AppSecret));
            var expectedSig = Convert.ToBase64String(sha256.ComputeHash(Encoding.UTF8.GetBytes(payload)));
            sha256.Clear();

            encodedSig = parameters[0].Length%4 == 0
                             ? parameters[0]
                             : parameters[0].PadRight(parameters[0].Length + (4 - parameters[0].Length%4), '=')
                                            .Replace("-", "+")
                                            .Replace("_", "/");
            payload = parameters[1].Length%4 == 0
                          ? parameters[1]
                          : parameters[1].PadRight(parameters[1].Length + (4 - parameters[1].Length%4), '=')
                                         .Replace("-", "+")
                                         .Replace("_", "/");


            if (encodedSig != expectedSig) {
                throw new WeiboException("SignedRequest签名验证失败。");
            }
            var result = JObject.Parse(Encoding.UTF8.GetString(Convert.FromBase64String(payload)));

            if (result["oauth_token"] == null) {
                return null; //throw new WeiboException("没有获取到授权信息，请先进行授权。");
            }

            var token = new AccessToken();
            AccessToken = token.Token = result["oauth_token"].ToString();


            token.UID = result["user_id"].ToString();
            token.ExpiresIn = Convert.ToInt32(result["expires"].ToString());
            return token;
        }