base64编码和解码

string Str = "abc";

// 编码
string BaseStr = Convert.ToBase64String(Encoding.UTF8.GetBytes(Str));

Console.WriteLine(BaseStr);// YWJj

// 解码
string OldStr = Encoding.GetEncoding("utf-8").GetString(Convert.FromBase64String(BaseStr));

Console.WriteLine(OldStr); // abc