Encoding/decoding algorithm from Metalogix Archive Manager (MAM)

EncodeUtils.cs

using System;

namespace Cryptography
{
    public class EncodeUtils
    {
        public static string Encode6bit(string txt)
        {
            short num = (short)txt.Length;
            string text = txt;
            short num2 = num % 3;
            if (num2 == 0)
            {
                num2 = 3;
            }
            for (int i = 0; i < (int)(3 - num2); i++)
            {
                text += " ";
            }
            string text2 = num.ToString("X").PadLeft(4, '0');
            byte[] array = new byte[8];
            for (int j = 0; j < (int)num; j += 3)
            {
                ushort num3 = (ushort)text[j];
                ushort num4 = (ushort)text[j + 1];
                ushort num5 = (ushort)text[j + 2];
                array[0] = (byte)((num3 & 64512) >> 10);
                array[1] = (byte)((num3 & 1008) >> 4);
                array[2] = (byte)((int)(num3 & 15) << 2 | (num4 & 49152) >> 14);
                array[3] = (byte)((num4 & 16128) >> 8);
                array[4] = (byte)((num4 & 252) >> 2);
                array[5] = (byte)((int)(num4 & 3) << 4 | (num5 & 61440) >> 12);
                array[6] = (byte)((num5 & 4032) >> 6);
                array[7] = (byte)(num5 & 63);
                for (int k = 0; k < 8; k++)
                {
                    byte b = array[k];
                    char c;
                    if (b < 10)
                    {
                        c = (char)(48 + b);
                    }
                    else if (b < 36)
                    {
                        c = (char)(97 + b - 10);
                    }
                    else if (b < 62)
                    {
                        c = (char)(65 + b - 36);
                    }
                    else if (b == 63)
                    {
                        c = '<';
                    }
                    else
                    {
                        c = '>';
                    }
                    text2 += c;
                }
            }
            return text2;
        }

        public static string Decode6bit(string txt)
        {
            string value = txt.Substring(0, 4);
            ushort num = Convert.ToUInt16(value, 16);
            int length = txt.Length;
            string text = "";
            ushort[] array = new ushort[8];
            for (int i = 4; i < length; i += 8)
            {
                for (int j = 0; j < 8; j++)
                {
                    char c = txt[i + j];
                    ushort num2;
                    if (c == '>')
                    {
                        num2 = 63;
                    }
                    else if (c == '<')
                    {
                        num2 = 62;
                    }
                    else if (c >= 'a')
                    {
                        num2 = (ushort)((byte)c - 97 + 10);
                    }
                    else if (c >= 'A')
                    {
                        num2 = (ushort)((byte)c - 65 + 36);
                    }
                    else
                    {
                        num2 = (ushort)((byte)c - 48);
                    }
                    array[j] = num2;
                }
                ushort num3 = (ushort)((int)array[0] << 10 | (int)array[1] << 4 | (array[2] & 60) >> 2);
                ushort num4 = (ushort)((int)(array[2] & 3) << 14 | (int)array[3] << 8 | (int)array[4] << 2 | (array[5] & 48) >> 4);
                ushort num5 = (ushort)((int)(array[5] & 15) << 12 | (int)array[6] << 6 | (int)array[7]);
                text += (char)num3;
                text += (char)num4;
                text += (char)num5;
            }
            if (text.Length > (int)num)
            {
                text = text.Substring(0, (int)num);
            }
            return text;
        }

        public static string EncodeXOR(string original, string key)
        {
            string text = "";
            for (int i = 0; i < original.Length; i++)
            {
                char value = original[i];
                int num = (int)Convert.ToByte(value);
                int num2 = (int)key[i % key.Length];
                text += (num ^ num2).ToString("X2");
            }
            return text;
        }

        public static string EncodeXORO365(string original)
        {
            return EncodeUtils.EncodeXOR(original, "<O365!!>");
        }

        public static string DecodeXOR(string encoded, string key)
        {
            string text = "";
            for (int i = 0; i < encoded.Length; i += 2)
            {
                int num = (int)Convert.ToByte(encoded.Substring(i, 2), 16);
                int num2 = (int)key[i / 2 % key.Length];
                int num3 = num ^ num2;
                text += (char)num3;
            }
            return text;
        }

        public static string DecodeXORO365(string original)
        {
            return EncodeUtils.DecodeXOR(original, "<O365!!>");
        }

    }
}