Supercell.GUT/Supercell.GUT.Titan/Encryption/RC4Encrypter.cs

namespace Supercell.GUT.Titan.Encryption;

public class RC4Encrypter
{
    private byte[]? m_key;
    private byte m_x;
    private byte m_y;

    public RC4Encrypter(string baseKey, string nonce)
    {
        this.InitState(baseKey, nonce);
    }

    public void InitState(string baseKey, string nonce)
    {
        string key = baseKey + nonce;

        this.m_key = new byte[256];
        this.m_x = 0;
        this.m_y = 0;

        for (int i = 0; i < 256; i++)
        {
            this.m_key[i] = (byte)i;
        }

        for (int i = 0, j = 0; i < 256; i++)
        {
            j = (byte)(j + this.m_key[i] + key[i % key.Length]);

            (this.m_key[j], this.m_key[i]) = (this.m_key[i], this.m_key[j]);
        }

        for (int i = 0; i < key.Length; i++)
        {
            this.m_x += 1;
            this.m_y += this.m_key[this.m_x];

            (this.m_key[this.m_x], this.m_key[this.m_y]) = (this.m_key[this.m_y], this.m_key[this.m_x]);
        }
    }

    public void Encrypt(byte[] input)
    {
        for (int i = 0; i < input.Length; i++)
        {
            this.m_x += 1;
            this.m_y += this.m_key![this.m_x];

            (this.m_key[this.m_x], this.m_key[this.m_y]) = (this.m_key[this.m_y], this.m_key[this.m_x]);
            input[i] = (byte)(input[i] ^ this.m_key[(byte)(this.m_key[this.m_x] + this.m_key[this.m_y])]);
        }
    }
}