public string GenerateSessionKey()
 {
     try
     {
         SecureRandom random = new SecureRandom();
         KeyGenerationParameters parameters = new KeyGenerationParameters(random,
         SYMMETRIC_KEY_SIZE);
         CipherKeyGenerator keyGenerator = GeneratorUtilities.GetKeyGenerator("AES");

         keyGenerator.Init(parameters);
         return Convert.ToBase64String(keyGenerator.GenerateKey());
     }
     catch (Exception ex)
     {
         throw new Exception(ex.ToString());
     }
 }
 
 
 public string GenerateSha256Hash(byte[] message)
 {
     try
     {
         IDigest digest = new Sha256Digest();
         digest.Reset();
         byte[] buffer = new byte[digest.GetDigestSize()];
         digest.BlockUpdate(message, 0, message.Length);
         digest.DoFinal(buffer, 0);

         return Convert.ToBase64String(buffer);
     }
     catch (Exception ex)
     {
         throw new Exception(ex.ToString());
     }
 }
 
 
 public string EncryptUsingPublicKey(byte[] data)
 {
     try
     {
         IBufferedCipher cipher = CipherUtilities.GetCipher(ASYMMETRIC_ALGO);
         cipher.Init(true, this.publicKey);
         return Convert.ToBase64String(cipher.DoFinal(data));
     }
     catch (Exception ex)
     {
         throw new Exception(ex.ToString());
     }
 }
 
 
 public string EncryptUsingSessionKey(byte[] skey, byte[] data)
 {
     try
     {
         PaddedBufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new AesEngine());
         
         cipher.Init(true, new KeyParameter(skey));
         byte[] sourceArray = new byte[cipher.GetOutputSize(data.Length)];
         int num2 = cipher.ProcessBytes(data, 0, data.Length, sourceArray, 0);
         int num3 = cipher.DoFinal(sourceArray, num2);
         byte[] destinationArray = new byte[num2 + num3];
         Array.Copy(sourceArray, 0, destinationArray, 0, destinationArray.Length);
         return Convert.ToBase64String(destinationArray);
     }
     catch (Exception ex)
     {
         throw new Exception(ex.ToString());
     }
 }
 
 
 //Method to posting data to server
  public async Task<HttpResponseMessage> CashWithdrawalAsync(CashWithdrawalModel model,Dictionary<string, string> dictionary)
  {
      string json = Converter.JsonSerializer(model);// JsonConvert.SerializeObject(model);

      string url = "fpaepsservice/api/cashWithdrawal/merchant/withdrawal";
      var client = new HttpClient();


      client.DefaultRequestHeaders.TryAddWithoutValidation(Constants.TransactionTimestamp, dictionary[Constants.TransactionTimestamp]);
      client.DefaultRequestHeaders.TryAddWithoutValidation(Constants.Hash, dictionary[Constants.Hash]);
      client.DefaultRequestHeaders.TryAddWithoutValidation(Constants.DeviceIMEI, dictionary[Constants.DeviceIMEI]);
      client.DefaultRequestHeaders.TryAddWithoutValidation(Constants.Eskey, dictionary[Constants.Eskey]);

      var response = await _apiManagerService.PostAsync(AppSettings.AepsBaseUrl, url, dictionary[Constants.EncryptedJson], client);

      return response;
  }