using System.Security.Cryptography;

using System.Text;

using System.Diagnostics;

using System;

​

namespace aes_gcm {

  class Program {

    // aes data in Base64 encoding, which will be transmitted and received

    public struct AESData {

      public string nonce;

      public string cipher;

      public string authTag;

      public string authData;

    }

    static void Main(string[] args) {

        Console.WriteLine("HERE");

      // all string <-> byte array conversions will use UTF8 encoding 

      // some non-ascii chars are added to auth data and plain text for testing purposes

      UTF8Encoding utf8enc = new UTF8Encoding();

      // console will use UTF8 encoding

      Console.OutputEncoding = utf8enc;

      // declare aes variables

      byte[] key = new byte[16];

      byte[] nonce = new byte[12];

      byte[] authTag = new byte[16];

      byte[] authData = utf8enc.GetBytes("handy-auth-data");

​

      // data to be transmitted and received in base64 encoding

      AESData aesData = new AESData();

      // randomly generate aes key

      using(RandomNumberGenerator rng = RandomNumberGenerator.Create()) {

        rng.GetBytes(key);

      }

​

      WriteByteArray("key", key);

      WriteByteArray("nonce", nonce);

      // assign plain text

      string plainText = "Hello AES/GCM!";

      Console.WriteLine("");

      // convert the plain text string to a byte array 

      byte[] plainBytes = utf8enc.GetBytes(plainText);

      WriteByteArray("plainBytes", plainBytes);

      // allocate the cipher text byte array as the same size as the plain text byte array

      byte[] cipher = new byte[plainBytes.Length];

      // perform encryption

      using(AesGcm aesgcm = new AesGcm(key)) aesgcm.Encrypt(nonce, plainBytes, cipher, authTag, authData);

      WriteByteArray("cipher", cipher);

      WriteByteArray("authTag", authTag);

      // encode aes data to Base64 strings, which will be transmitted

      aesData.nonce = System.Convert.ToBase64String(nonce);

      aesData.cipher = System.Convert.ToBase64String(cipher);

      aesData.authTag = System.Convert.ToBase64String(authTag);

      aesData.authData = System.Convert.ToBase64String(authData);

​

      // print aes data

      Console.WriteLine("*** AES data ***");

      Console.WriteLine("Key : {System.Convert.ToBase64String(key)}");

      Console.WriteLine("Nonce : {aesData.nonce}");

      Console.WriteLine("AuthTag : {aesData.authTag}");

      Console.WriteLine("AuthData : {aesData.authData}");

      Console.WriteLine("");

​

      Console.WriteLine("PlainText : {plainText}");

      Console.WriteLine("EncryptedText : {aesData.cipher}");

      Console.WriteLine("");

      // decode received Base64 strings to aes data 

      nonce = System.Convert.FromBase64String(aesData.nonce);

      cipher = System.Convert.FromBase64String(aesData.cipher);

      authTag = System.Convert.FromBase64String(aesData.authTag);

      authData = System.Convert.FromBase64String(aesData.authData);

      // allocate the decrypted text byte array as the same size as the plain text byte array 

      byte[] decryptedBytes = new byte[cipher.Length]; // perform decryption

      using(AesGcm aesgcm = new AesGcm(key)) aesgcm.Decrypt(nonce, cipher, authTag, decryptedBytes, authData);

      WriteByteArray("decryptedBytes", decryptedBytes);

      // convert the byte array to the plain text string 

      string decryptedText = utf8enc.GetString(decryptedBytes);

      Console.WriteLine("decryptedText = '{0}'", decryptedText);

      Console.WriteLine("");

    }

    static void WriteByteArray(string name, byte[] byteArray) {

      Console.WriteLine("\"{0}\", {1} bytes, {2} bits:", name, byteArray.Length, byteArray.Length << 3);

      Console.WriteLine("");

      Console.WriteLine("");

    }

  }

}

​

​