algorithmOriginalWork.cs

/*
Copyright 2020, Ludwig V. <https://github.com/ludwig-v>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License at <http://www.gnu.org/licenses/> for
more details.

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
*/

using System;
					
public class Program
{
	public static string getKey(string seedTXT, string appKeyTXT) {
		string result = "";
		
		string[] seed = {seedTXT.Substring(0,2), seedTXT.Substring(2,2), seedTXT.Substring(4,2), seedTXT.Substring(6,2)};
		string[] appKey = {appKeyTXT.Substring(0,2), appKeyTXT.Substring(2,2)};

		long x = 0;
		long a = 0;
		long b = 0;
		long c = 0;
		long d = 0;
		long appKeyComputed = 0;
		long val = 0;
		long key = 0;
		long key_ = 0;

		x = int.Parse(appKey[0]+appKey[1], System.Globalization.NumberStyles.HexNumber);
		a = int.Parse(appKey[1]+"00"+appKey[0]+appKey[1], System.Globalization.NumberStyles.HexNumber) * 0xAA;
		if (x > 0x7FFF) {
			b = ((0x0B81702E1 * (0xFFFFFFFF0000 | x)) >> 32);
			b = ((0xFFFF0000 | (b & 0xffff)) >> 7) + 0xFE000000;
		} else {
			b = ((0x0B81702E1 * x) >> 32) >> 7; 
		}
		c = ((b + (b >> 0x1F)) & 0xffff) * 0x7673;
		d = a - c;
		if ((d & 0xffff) > 0x7FFF) { // Negative
			d += 0x7673;
		}
		appKeyComputed = (d & 0xffff);

		x = int.Parse(seed[0]+seed[3], System.Globalization.NumberStyles.HexNumber);
		a = x * 0xAB;
		if (x > 0x7FFF) {
			b = ((0x0B92143FB * (0xFFFFFFFF0000 | x)) >> 32);
			b = ((0xFFFF0000 | (b & 0xffff)) >> 7) + 0xFE000000;
		} else {
			b = ((0x0B92143FB * x) >> 32) >> 7; 
		}
		c = ((b + (b >> 0x1F)) & 0xffff) * 0x763D;
		d = a - c;
		if ((d & 0xffff) > 0x7FFF) { // Negative
			d += 0x763D;
		}
		d = (d & 0xffff);
		key = d | appKeyComputed;

		x = int.Parse(seed[1]+seed[2], System.Globalization.NumberStyles.HexNumber);
		a = x * 0xAA;
		if (x > 0x7FFF) {
			b = ((0x0B81702E1 * (0xFFFFFFFF0000 | x)) >> 32);
			b = ((0xFFFF0000 | (b & 0xffff)) >> 7) + 0xFE000000;
		} else {
			b = ((0x0B81702E1 * x) >> 32) >> 7; 
		}
		c = ((b + (b >> 0x1F)) & 0xffff) * 0x7673;
		d = a - c;
		if ((d & 0xffff) > 0x7FFF) { // Negative
			d += 0x7673;
		}
		d = (d & 0xffff);

		val = d;

		x = (key & 0xffff);
		a = x * 0xAB;
		if (x > 0x7FFF) {
			b = ((0x0B92143FB * (0xFFFFFFFF0000 | x)) >> 32);
			b = ((0xFFFF0000 | (b & 0xffff)) >> 7) + 0xFE000000;
		} else {
			b = ((0x0B92143FB * x) >> 32) >> 7;
		}
		c = ((b + (b >> 0x1F)) & 0xffff) * 0x763D;
		d = a - c;
		if ((d & 0xffff) > 0x7FFF) { // Negative
			d += 0x763D;
		}
		d = (d & 0xffff);

		key_ = (val | d);

		result = key.ToString("X4") + key_.ToString("X4");
		
		return result;
	}
	
	public static void Main()
	{
		Console.WriteLine(getKey("11111111", "D91C"));
	}
}