# [rev] Guesser - Tamil CTF 2021

###### tags: `TamilCTF2021` `rev`

Executable written using .NET Framework is distributed. It can be reversed using tool like ILSpy.

// App.Program
using System;

internal class Program
{
	private static void function_two(string user, string pass)
	{
		if (user[2] + user[0] == 182 && user[2] - user[3] == 10 && user[4] == 'R' && user[4] - user[5] == 34 && user[6] - 16 == 100)
		{
			Console.WriteLine("\n  [+] Congratulation.Credentials are correct!! [+]\n\n----- The Flag is TamilCTF{username:password} -----\n");
		}
	}

	private static void function_one(string username, string password)
	{
		if ((password[2] ^ 0x17) == 124 && password[4] + password[2] == 192 && password[3] - 14 == 103)
		{
			function_two(username, password);
		}
	}

	private static void check(string user, string pass)
	{
		if (user.Length != 7)
		{
			Console.WriteLine("\nWrong username :( \n");
		}
		else if (pass.Length != 5)
		{
			Console.WriteLine("\nWrong password :( \n");
		}
		else if ((user[0] ^ 0x39) == 114 && pass[0] - 17 == 54 && user[0] + user[1] == 127 && (pass[0] ^ pass[1]) == 119)
		{
			function_one(user, pass);
		}
	}

	private static void Main(string[] args)
	{
		Console.WriteLine("\n---------------------------------------------------");
		Console.WriteLine("--------------------   Login   --------------------");
		Console.WriteLine("---------------------------------------------------\n");
		Console.Write("    Enter the Username : ");
		string user = Console.ReadLine();
		Console.Write("    Enter the Password : ");
		string pass = Console.ReadLine();
		check(user, pass);
	}
}

Username and password is recoverable from this.

print('Username: ' + chr(114 ^ 0x39) + chr(127 - (114 ^ 0x39)) + chr(182 - (114 ^ 0x39)) + chr((182 - (114 ^ 0x39)) - 10) + 'R' + chr(ord('R') - 34) + chr(116))
# Username: K4kaR0t
print('Password: ' + chr(71) + chr(119 ^ 71) + chr(124 ^ 0x17) + chr(117) + chr(192 - (124 ^ 0x17)))
# Password: G0kuU

From the overall information, flag is `TamilCTF{K4kaR0t:G0kuU}`.