Simple crackme example

crackme.cs

// Simple crackme example by drakonia 

Console.WriteLine("Enter the correct password:");
string? solution = null;
while (solution == null)
{
    string? input = Console.ReadLine();
    solution = Verify(input);
}

Console.WriteLine($"The password is: {solution} Good job :)");
Console.ReadKey();


static string? Verify(string? input)
{
    // Skip any checks if the input is invalid
    if (input == null)
        return null;

    // This is our key in encrypted form
    char[] secret =
    {
        'ä', 'ù', 'å', 'è', 'î', 'æ', 'î', 'Õ', 'Ý', 'è', 'þ', 'Ñ', 'ì', 'ø', 'â', 'ù', 'Ì', 'ù', 'Ö', 'É', 'æ', 'Ç',
        '×', 'Û', 'Þ', 'ā',
    };

    // hint that the password is the same length as secret
    if (input.Length != secret.Length)
        return null;

    // Buffer that will hold the encrypted form of input
    char[] buffer = new char[input.Length];

    // Encrypt the user input
    for (int i = 0; i < input.Length; i++)
    {
        char c = input[i];
        c += (char) 0xEA;
        c ^= (char) 0x7E;
        c -= (char) (0x5B + i);
        buffer[i] = c;
    }

    int sum = 0;
    // Compare the encrypted user input to secret
    for (int i = 0; i < buffer.Length; i++)
    {
        sum |= buffer[i] ^ secret[i];
    }

    if (sum == 0)
        return input;

    // Return null if input does not match secret
    return null;
}

This is an example of how to make a .net crackme without using string equality comparisons

Article about the topic: https://dr4k0nia.github.io/dotnet/reverse-engineering/2022/01/25/Some-thoughts-on-making-a-crackme.html