Can anyone tell me the Key/Modifires below I'm really new to C#

im trying to learn what the keys and Modifires are iv tried google and such but i can never
find anything..

this code was given to me by my buddy i would ask him but he was shipped off about a week ago.

Code:
{
    using System;
    using System.IO;

    internal class EncryptionStandard : ITableEncryption
    {
        void ITableEncryption.Decode(ref byte[] data)
        {
            uint num = 0x816;
            for (int i = 0; i < data.Length; i++)
            {
                byte num3 = data[i];
                uint num4 = num;
                byte num5 = 0;
                num4 &= 0xff00;
                num4 = num4 >> 8;
                num5 = (byte) (num4 ^ num3);
                num4 = num3;
                num4 += num;
                num4 &= 0xffff;
                num4 *= 0x6081;
                num4 &= 0xffff;
                num4 += 0x1608;
                num4 &= 0xffff;
                num = num4;
                data[i] = num5;
            }
        }

        void ITableEncryption.Encode(FileStream stream)
        {
            int num = stream.ReadByte();
            uint num2 = 0x816;
            while (num != -1)
            {
                stream.Seek(-1L, SeekOrigin.Current);
                byte num3 = (byte) (num & 0xff);
                byte num4 = 0;
                uint num5 = num2;
                num5 &= 0xff00;
                num5 = num5 >> 8;
                num4 = (byte) (num5 ^ num3);
                num5 = num4;
                num5 += num2;
                num5 &= 0xffff;
                num5 *= 0x6081;
                num5 &= 0xffff;
                num5 += 0x1601;
                num5 &= 0xffff;
                num2 = num5;
                stream.WriteByte(num4);
                num = stream.ReadByte();
            }
        }

        string ITableEncryption.Details
        {
            get
            {
                return "The standard encryption method.";
            }
        }

        string ITableEncryption.Name
        {
            get
            {
                return "Standard";
            }
        }
    }
}