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using System;

using System.Text;

using Org.BouncyCastle.Crypto.Engines;

using Org.BouncyCastle.Crypto.Modes;

using Org.BouncyCastle.Crypto.Parameters;

using NeoSmart.Utils;

​

public class HelloWorld

{

    public static void Main(string[] args)

    {

        string encoded_key= "ZneN1NKt22Q/NNZBA8se6dxmATjRKouWq6ecpRsL/50=";

        string encoded_iv= "edHnM2KFhIqrPBk0";

        string Text = "{\"entity_id\":\"100\",\"member_id\":\"2165464\",\"email\":\"arun.p@neubergdiagnostics.com\",\"first_name\":\"Arun\",\"last_name\":\"P\",\"gender\":\"M\",\"mobile\":\"9600960461\",\"dob\":\"19-07-1993\",\"requested_at\":\"1686294340\"}";

        byte[] encryptedBytes = encrypt(Text, Convert.FromBase64String(encoded_key), Convert.FromBase64String(encoded_iv));

        string encodedText = UrlBase64.Encode(encryptedBytes, PaddingPolicy.Preserve);

        Console.WriteLine ("\nEncrypted combined payload:\n" + encodedText);

        //split encryptedBytes to message & auth tag, considering encryptedBytes as combined payload

        byte[] encryptedMessage = new byte[encryptedBytes.Length - 16];

        byte[] encryptedAuthTag = new byte[16];

        Array.Copy(encryptedBytes, 0, encryptedMessage, 0, encryptedMessage.Length);

        Array.Copy(encryptedBytes, encryptedMessage.Length, encryptedAuthTag, 0, encryptedAuthTag.Length);

        string encodedMessage  = UrlBase64.Encode(encryptedMessage, PaddingPolicy.Preserve);

        string encodedAuthTag  = UrlBase64.Encode(encryptedAuthTag, PaddingPolicy.Preserve);

        Console.WriteLine ("\nEncrypted message:\n" + encodedMessage);  

        Console.WriteLine ("\nAuthentication tag:\n" + encodedAuthTag); 

        //Decrypt after combining two message+auth_tag which were split & sent

        byte[] combinedBytes = new byte[encryptedMessage.Length + encryptedAuthTag.Length];

        System.Buffer.BlockCopy(encryptedMessage, 0, combinedBytes, 0, encryptedMessage.Length);

        System.Buffer.BlockCopy(encryptedAuthTag, 0, combinedBytes, encryptedMessage.Length, encryptedAuthTag.Length);

        string res = decrypt(UrlBase64.Encode(combinedBytes, PaddingPolicy.Preserve), Convert.FromBase64String(encoded_key), Convert.FromBase64String(encoded_iv));

        Console.WriteLine ("\nDecrypted message:\n" + res);

        //decrypt combined payload from encrption

        res = decrypt(encodedText, Convert.FromBase64String(encoded_key), Convert.FromBase64String(encoded_iv));

        Console.WriteLine ("\nDecrypted combined payload:\n" + res);

    }

    public static byte[] encrypt(string PlainText, byte[] key, byte[] iv)

    {

        byte[] encryptedBytes = null;

        try

        {

            byte[] plainBytes = Encoding.UTF8.GetBytes(PlainText);              

            GcmBlockCipher cipher = new GcmBlockCipher(new AesEngine());

            AeadParameters parameters = 

                         new AeadParameters(new KeyParameter(key), 128, iv, null);

            cipher.Init(true, parameters);

            encryptedBytes = new byte[cipher.GetOutputSize(plainBytes.Length)];

            int retLen = cipher.ProcessBytes

                           (plainBytes, 0, plainBytes.Length, encryptedBytes, 0);

            cipher.DoFinal(encryptedBytes, retLen);

        }

        catch (Exception ex)

        {

            Console.WriteLine(ex.Message);

            Console.WriteLine(ex.StackTrace);

        }

        return encryptedBytes;

    }

    public static string decrypt(string encodedText, byte[] key, byte[] iv)

    {

        string sR = string.Empty;

        try

        {

            byte[] encryptedBytes = UrlBase64.Decode(encodedText);

            GcmBlockCipher cipher = new GcmBlockCipher(new AesEngine());

            AeadParameters parameters = 

                new AeadParameters(new KeyParameter(key), 128, iv, null);

            cipher.Init(false, parameters);

            byte[] plainBytes = new byte[cipher.GetOutputSize(encryptedBytes.Length)];

            Int32 retLen = cipher.ProcessBytes

                (encryptedBytes, 0, encryptedBytes.Length, plainBytes, 0);

            cipher.DoFinal(plainBytes, retLen);

​

            sR = Encoding.UTF8.GetString(plainBytes);

        }

        catch (Exception ex)

        {

            Console.WriteLine(ex.Message);

            Console.WriteLine(ex.StackTrace);

        }

        return sR;

    }

}