using System;

using System.Security.Cryptography;

using Sodium;

​

public static class Program

{

    public static void Main() {

    Console.WriteLine("Libsodium secret box random key string encryption");

    // you need the library https://www.nuget.org/packages/Sodium.Core/ version 1.2.3

​

    string plaintext = "The quick brown fox jumps over the lazy dog";

    Console.WriteLine("plaintext: " + plaintext);

    string keyBase64 = Base64Encoding(GenerateRandomKey());         

    Console.WriteLine("keyBase64): " + keyBase64);      

​

    // encrypt

    string ciphertextBase64 = SecretboxEncryptionToBase64(keyBase64, plaintext);

    Console.WriteLine("\n* * * encryption * * *");

    Console.WriteLine("all data are in Base64 encoding");

    Console.WriteLine("ciphertext:  " + ciphertextBase64);

    Console.WriteLine("output is (Base64) nonce : (Base64) ciphertext");

​

    // decrypt

    string ciphertextReceivedBase64 = ciphertextBase64;

    string decryptedtext = SecretboxDecryptionFromBase64(keyBase64, ciphertextReceivedBase64);

    Console.WriteLine("\n* * * decryption * * *");

    Console.WriteLine("ciphertext:  " + ciphertextReceivedBase64);

    Console.WriteLine("input is (Base64) nonce : (Base64) ciphertext");

    Console.WriteLine("decrypt.text:" + decryptedtext);

}

    static string SecretboxEncryptionToBase64(string keyBase64, string plaintext){

        byte[] nonce = GenerateRandomNonce();

        byte[] data = System.Text.Encoding.UTF8.GetBytes(plaintext);        

        byte[] ciphertext = SecretBox.Create(plaintext, nonce, Base64Decoding(keyBase64));

      return Base64Encoding(nonce) + ":" + Base64Encoding(ciphertext);

    }

    static string SecretboxDecryptionFromBase64(string keyBase64, string ciphertextReceivedBase64){

      String[] parts = ciphertextReceivedBase64.Split(':');

      byte[] nonce = Base64Decoding(parts[0]);

      byte[] ciphertext = Base64Decoding(parts[1]);

      var decrypted = SecretBox.Open(ciphertext, nonce, Base64Decoding(keyBase64)); 

      return System.Text.Encoding.UTF8.GetString(decrypted, 0, decrypted.Length);

  }   

    static byte[] GenerateRandomKey() {

        RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();

        byte[] key = new byte[32];

        rngCsp.GetBytes(key);

        return key;

    }

​

    static byte[] GenerateRandomNonce() {

       RNGCryptoServiceProvider rngCsp = new RNGCryptoServiceProvider();

       byte[] nonce = new byte[24];

       rngCsp.GetBytes(nonce);

       return nonce;

    }   

    private static string Base64Encoding(byte[] input) {

        return Convert.ToBase64String(input);

    }

​

    private static byte[] Base64Decoding(String input) {

        return Convert.FromBase64String(input);

    }

}