I’m trying to write some encryption code that is passed through a Url. For the sake of the issue I’ve excluded the actual encryption of the data and just shown the code causing the problem.

I take a salt value, convert it to a byte array and then convert that to a base64 string. This string I concatenate to another base64 string (which was previously a byte array).

These two base64 strings are then Url encoded. Here’s my code...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;
using System.IO;
using System.Web;

class RHEncryption
{
    private static readonly Encoding ASCII_ENCODING = new System.Text.ASCIIEncoding();
    private static readonly string SECRET_KEY = "akey";
    private static string md5(string text)
    {
        return BitConverter.ToString(new MD5CryptoServiceProvider().ComputeHash(ASCII_ENCODING.GetBytes(text))).Replace("-", "").ToLower();
    }

    public string UrlEncodedData;

    public RHEncryption()
    {
        // encryption object
        RijndaelManaged aes192 = new RijndaelManaged();
        aes192.KeySize = 192;
        aes192.BlockSize = 192;            
        aes192.Mode = CipherMode.CBC;
        aes192.Key = ASCII_ENCODING.GetBytes(md5(SECRET_KEY));
        aes192.GenerateIV();

        // convert Ivector to base64 for sending            
        string base64IV = Convert.ToBase64String(aes192.IV);

        // salt value
        string s = "maryhadalittlelamb";
        string salt = s.Substring(0, 8);
        // convert to byte array
        // and base64 for sending
        byte[] saltBytes = ASCII_ENCODING.GetBytes(salt.TrimEnd('\0'));
        string base64Salt = Convert.ToBase64String(saltBytes);

        //url encode concatenated base64 strings
        UrlEncodedData = HttpUtility.UrlEncode(base64Salt + base64IV, ASCII_ENCODING);
    }

    public string UrlDecodedData()
    {
        // decode the url encode string
        string s = HttpUtility.UrlDecode(UrlEncodedData, ASCII_ENCODING);

        // convert back from base64
        byte[] base64DecodedBytes = null;
        try
        {
            base64DecodedBytes = Convert.FromBase64String(s);
        }
        catch (FormatException e)
        {
            Console.WriteLine(e.Message.ToString());
            Console.ReadLine();
        }
        return s;
    }
}

If I then call the UrlDecodedData method I get a “Invalid character in a Base-64 string” exception. This is generated because the base64Salt variable contains an invalid character (I’m guessing a line termination) but I can’t seem to strip it off.