using System;

using System.Security.Cryptography;

using Sodium;

public static class Program

{

    public static void Main()

    {

        // you need this library libsodium-core/sodium.core version 1.2.3

        // get it from here: https://www.nuget.org/packages/Sodium.Core/ - https://github.com/tabrath/libsodium-core/ libsodium-core

        Console.WriteLine("Libsodium crypto box hybrid string encryption");

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

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

        // encryption

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

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

        // for encryption you need your private key (privateKeyA) and the public key from other party (publicKeyB)

        string privateKeyABase64 = "yJIzp7IueQOu8l202fwI21/aNXUxXBcg3jJoLFJATlU=";

        string publicKeyBBase64 =  "jVSuHjVH47PMbMaAxL5ziBS9/Z0HQK6TJLw9X3Jw6yg=";

        // convert the base64 encoded keys

        byte[] privateKeyA = Base64Decoding(privateKeyABase64);

        byte[] publicKeyB = Base64Decoding(publicKeyBBase64);

        string ciphertextBase64 = SecretboxEncryptionToBase64(privateKeyA, publicKeyB, plaintext);

        Console.WriteLine("privateKeyA: " + privateKeyABase64);

        Console.WriteLine("publicKeyB:  " + publicKeyBBase64);

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

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

​

        // decryption

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

        string ciphertextReceivedBase64 = ciphertextBase64;

        // for decryption you need your private key (privateKeyB) and the public key from other party (publicKeyA)

        string privateKeyBBase64 = "yNmXR5tfBXA/uZjanND+IYgGXlrFnrdUiUXesI4fOlM=";

        string publicKeyABase64 =  "b+Z6ajj7wI6pKAK5N28Hzp0Lyhv2PvHofwGY3WSm7W0=";

        // convert the base64 encoded keys

        byte[] privateKeyB = Base64Decoding(privateKeyBBase64);

        byte[] publicKeyA = Base64Decoding(publicKeyABase64);

        string decryptedtext = SecretboxDecryptionFromBase64(privateKeyA, publicKeyB, ciphertextReceivedBase64);

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

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

        Console.WriteLine("privateKeyB: " + privateKeyBBase64);

        Console.WriteLine("publicKeyA:  " + publicKeyBBase64);

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

​

​

    }

    private static string SecretboxEncryptionToBase64(byte[] privateKey, byte[] publicKey, string plaintext){

        byte[] nonce = GenerateRandomNonce();

        return Base64Encoding(nonce) + ":" + Base64Encoding(PublicKeyBox.Create(plaintext, nonce, privateKey, publicKey));

    }   

    private static string SecretboxDecryptionFromBase64(byte[] privateKey, byte[] publicKey, string ciphertextBase64) {

        string[] parts = ciphertextBase64.Split(':');

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

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

        var decrypted = PublicKeyBox.Open(ciphertext, nonce, privateKey, publicKey);    

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

    }       

    private 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);

    }

}