如何解码base64编码的字符串？

Question

我试图"解码"以下Base64字符串:

OBFZDTcPCxlCKhdXCQ0kMQhKPh9uIgYIAQxALBtZAwUeOzcdcUEeW0dMO1kbPElWCV1ISFFKZ0kdWFlLAURPZhEFQVseXVtPOUUICVhMAzcfZ14AVEdIVVgfAUIBWVpOUlAeaUVMXFlKIy9rGUN0VF08Oz1POxFfTCcVFw1LMQNbBQYWAQ ==

这就是我对字符串本身的了解:

1. 原始字符串首先通过以下代码传递:

   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());
   }
   

   p1代码中的部分应该是字符串" _p0lizei.".

2. 然后通过以下代码将其转换为Base64字符串:

   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;
   }
   

问题是,如何解码Base64字符串,以便我可以找出原始字符串是什么？

Answer 1

简单:

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

Answer 2

该m000493方法似乎执行某种XOR加密.这意味着可以使用相同的方法来加密和解密文本.你所要做的就是逆转m0001cd:

string p0 = Encoding.UTF8.GetString(Convert.FromBase64String("OBFZDT..."));

string result = m000493(p0, "_p0lizei.");
//    result == "gaia^unplugged^Ta..."

与return m0001cd(builder3.ToString());改变return builder3.ToString();.

Answer 3

    // Decode a Base64 string to a string
    public static string DecodeBase64(string value)
    {
        if(string.IsNullOrEmpty(value))
            return string.Empty;
        var valueBytes = System.Convert.FromBase64String(value);
        return System.Text.Encoding.UTF8.GetString(valueBytes);
    }