this is the source code of class Crypto
----------
using System;
    using System.Reflection;
    using System.Text;
    using System.Web.Configuration;
    using System.Web.Security;

    public class Crypto
    {
        public Crypto()
        {
        }

        // Fields
        private MethodInfo _EncDecMethod = null;

        // Methods
        public string Decrypt(string data)
        {
            string str;
            Initialize();
            try
            {
                byte[] buffer = Convert.FromBase64String(data);
                object[] parameters = new object[5];
                parameters[0] = false;
                parameters[1] = buffer;
                parameters[3] = 0;
                parameters[4] = buffer.Length;
                byte[] bytes = (byte[])_EncDecMethod.Invoke(null, parameters);
                str = Encoding.UTF8.GetString(bytes);
            }
            catch
            {
                throw new Exception("Failed to encrypt data.");
            }
            return str;
        }

        public string Encrypt(byte[] bytes)
        {
            string str = "";
            Initialize();
            try
            {
                object[] parameters = new object[5];
                parameters[0] = true;
                parameters[1] = bytes;
                parameters[3] = 0;
                parameters[4] = bytes.Length;
                byte[] inArray = (byte[])_EncDecMethod.Invoke(null, parameters);
                str = Convert.ToBase64String(inArray);
            }
            catch
            {
                throw new Exception("Failed to encrypt data.");
            }
            return str;
        }

        private void Initialize()
        {
            try
            {
                _EncDecMethod = typeof(MachineKeySection).GetMethod("EncryptOrDecryptData",
                    BindingFlags.NonPublic | BindingFlags.Static,
                    Type.DefaultBinder,
                    new Type[] { typeof(bool), typeof(byte[]), typeof(byte[]), typeof(int), typeof(int) }, null);
            }
            catch
            {
                throw new Exception("Failed to initialized base encryption method.");
            }
        }

        public string Encode(string pass, string salt)
        {
            byte[] bytes = Encoding.Unicode.GetBytes(pass);
            byte[] src = Convert.FromBase64String(salt);
            byte[] data = new byte[src.Length + bytes.Length];
            Buffer.BlockCopy(src, 0, data, 0, src.Length);
            Buffer.BlockCopy(bytes, 0, data, src.Length, bytes.Length);

            string s = Encrypt(data);
            return s;
        }
    }
-----------

for more detail : http://coder.awas.vn/Home/Topic/353-Dat-mat-khau-cho-tai-khoan-host-cua-DNN.aspx

@Sebastian : The diffrent is, you dont have to follow the rule of DNN pass word. You can enter only one letter "1" for your password or leave blank. And we dont have to create a new member eachtime we forgot the password of admin.