using System;

using System.Security.Cryptography;

using System.Text;

​

namespace AES256GCMDecrypt

{

    class Program

    {

        static void Main(string[] args)

        {

            // This is the encrypted string that you provided

            string encryptedString = "a6c0952b78967559-2953e738b9b005028bf4f6c0-7b8464d1ed75bc38b4503f6c8d25d6bfc22a19cc1a8a92bc6faa1ed6cd837b97072bc8e16fd95b6cfca67fccbad8fc";

​

            // This is the passphrase that you provided

            string passphrase = "this-is-a-test-passphrase";

            string[] splitStrs = encryptedString.Split('-');

​

            byte[] salt = Convert.FromHexString(splitStrs[0]);

            byte[] iv = Convert.FromHexString(splitStrs[1]);

            byte[] encryptedData = Convert.FromHexString(splitStrs[2]);

            // Extract the tag from the encrypted byte array

            byte[] tag = new byte[16];

            Array.Copy(encryptedData, encryptedData.Length - 16, tag, 0, 16);

            byte[] key = new Rfc2898DeriveBytes(passphrase, salt, 1000, HashAlgorithmName.SHA256).GetBytes(32);

           // Create an AesGcm object

            AesGcm aesGcm = new AesGcm(key);

            int textLength = encryptedData.Length;

​

            // Decrypt the ciphertext

            byte[] plaintext = new byte[textLength];

            aesGcm.Decrypt(iv, encryptedData, tag, plaintext);

​

            // Convert the plaintext to a string and print it

            string decryptedString = Encoding.UTF8.GetString(plaintext);

            Console.WriteLine(decryptedString);

        }

    }

}

​