我该如何去code一个base64连接codeD字符串？

我想去code这样的Base64如下字符串：

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

OBFZDTcPCxlCKhdXCQ0kMQhKPh9uIgYIAQxALBtZAwUeOzcdcUEeW0dMO1kbPElWCV1ISFFKZ0kdWFlLAURPZhEFQVseXVtPOUUICVhMAzcfZ14AVEdIVVgfAUIBWVpOUlAeaUVMXFlKIy9rGUN0VF08Oz1POxFfTCcVFw1LMQNbBQYWAQ==

OBFZDTcPCxlCKhdXCQ0kMQhKPh9uIgYIAQxALBtZAwUeOzcdcUEeW0dMO1kbPElWCV1ISFFKZ0kdWFlLAURPZhEFQVseXVtPOUUICVhMAzcfZ14AVEdIVVgfAUIBWVpOUlAeaUVMXFlKIy9rGUN0VF08Oz1POxFfTCcVFw1LMQNbBQYWAQ==

这是我所知道的字符串本身：

This is what I know about the string itself:

1. 原始字符串首先通过以下code通过：

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());
}

在code中的 P1 部分应该是字符串 _p0lizei。

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

然后它被下列code转成Base64字符串：

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;
}

现在的问题是，我怎么去code为Base64字符串，这样我可以找出原始字符串是什么？

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