How do I decode a base64 encoded string?

Rickard picture Rickard · Aug 20, 2011 · Viewed 337.9k times · Source

I am trying to "decode" this following Base64 string:

OBFZDTcPCxlCKhdXCQ0kMQhKPh9uIgYIAQxALBtZAwUeOzcdcUEeW0dMO1kbPElWCV1ISFFKZ0kdWFlLAURPZhEFQVseXVtPOUUICVhMAzcfZ14AVEdIVVgfAUIBWVpOUlAeaUVMXFlKIy9rGUN0VF08Oz1POxFfTCcVFw1LMQNbBQYWAQ==

This is what I know about the string itself:

  1. The original string is first passed through the following code:

    private static string m000493(string p0, string p1)
    {
        StringBuilder builder = new StringBuilder(p0);
        StringBuilder builder2 = new StringBuilder(p1);
        StringBuilder builder3 = new StringBuilder(p0.Length);
        int num = 0;
    Label_0084:
        while (num < builder.Length)
        {
            int num2 = 0;
            while (num2 < p1.Length)
            {
                if ((num == builder.Length) || (num2 == builder2.Length))
                {
                    MessageBox.Show("EH?");
                    goto Label_0084;
                }
                char ch = builder[num];
                char ch2 = builder2[num2];
                ch = (char)(ch ^ ch2);
                builder3.Append(ch);
                num2++;
                num++;
            }
        }
        return m0001cd(builder3.ToString());
    }
    

    The p1 part in the code is supposed to be the string "_p0lizei.".

  2. It is then converted to a Base64 string by the following code:

    private static string m0001cd(string p0)
    {
        string str2;
        try
        {
            byte[] buffer = new byte[p0.Length];
            str2 = Convert.ToBase64String(Encoding.UTF8.GetBytes(p0));
        }
        catch (Exception exception)
        {
            throw new Exception("Error in base64Encode" + exception.Message);
        }
        return str2;
    }
    

The question is, how do I decode the Base64 string so that I can find out what the original string is?

Answer

Matthew Abbott picture Matthew Abbott · Aug 20, 2011

Simple:

byte[] data = Convert.FromBase64String(encodedString);
string decodedString = Encoding.UTF8.GetString(data);