gistfile1.cs

static void TestSymmetric()
    {
        // First we create a nonce specify the nonce and fill it with random values
        var nonce = new byte[CryptoSecretBox.NonceBytes];
        RandomNumberGenerator rng = RandomNumberGenerator.Create();
        rng.GetBytes(nonce);
 
        // Then we create a secret key
        var key = new byte[CryptoSecretBox.KeyBytes];
        rng.GetBytes(key);
 
        //the secret message!!!
        var message = "winter is coming";
 
        //normal operations:
        try
        {
            //encrypt
            byte[] cypertext = EncryptSecretKey(message, key, nonce);
 
            //decrypt
            string decrypted = DecryptSecretKey(cypertext, key, nonce);
 
            //test
            if (decrypted == message)
            {
                Debug.Print("OK! the text matches");
            }
            else
            {
                Debug.Print("ERROR: this should NOT happen, ouch, the decyphered text is wrong!");
            }
        }
        catch (Exception ex)
        {
            Debug.Print("ERROR: this should NOT happen!");
        }
 
        try
        {
            byte[] cypertext = EncryptSecretKey(message, key, nonce);
 
            //just changes a byte in the cyphertext:
            cypertext[4] =1;
 
            string decrypted = DecryptSecretKey(cypertext, key, nonce);
            Debug.Print("this should never be executed!");
 
        }
        catch (Exception ex)
        {
            Debug.Print(" this error SHOULD happen, the cyphertext has been tampered with, yay!");
        }
 
 
        try
        {
            byte[] cypertext = EncryptSecretKey(message, key, nonce);
 
            //wrong key:
            key[4] = 0;
 
            string decrypted = DecryptSecretKey(cypertext, key, nonce);
            Debug.Print("this should never be executed!");
 
        }
        catch (Exception ex)
        {
            Debug.Print("this error SHOULD happen, the key has been changed, yay!");
        }
 
        
    }