rc4.h

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/*
**  Command & Conquer Generals Zero Hour(tm)
**  Copyright 2025 Electronic Arts Inc.
**
**  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 for more details.
**
**  You should have received a copy of the GNU General Public License
**  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
 
#ifndef RC4_H
#define RC4_H
 
//
// RC4.h - Implementation of RC4 encryption
//
//  RC4 is a stream cypher.  This means that it basically produces a stream of
//      random bytes that you XOR with your data.  Each key is somewhat like a
//      one time pad.
//
//  Just as you should never re-use a one time pad, you should never re-use a key.
//
//  If you can't re-exchange a secret key before every message you could keep a
//      partial secret key and then include the other part of the key in plaintext.
//      The key would be the concatenation of the two parts of the key. 
//
 
class RC4Class
{
public:
 
    RC4Class();
 
    //
    // Key length can be 0..256 bytes
    // Key preparation takes about 0.015 Ms on a 1Ghz PC
    // It's 3x faster if your keylen is 8 or 16 bytes!
    //
    void Prepare_Key(const unsigned char *key_data_ptr, int key_data_len);
 
    //
    // In-place encryption.  Call Prepare_Key first!
    // Only a few clock cycles per byte (9 or so...)
    //
    void RC4(unsigned char *buffer_ptr, int buffer_len);
 
 
    //
    // Copy state & key
    //
    RC4Class &operator=(const RC4Class &other);
 
 
    void Print_State(void);
 
private:
    void Prepare_Key_16bytes(const unsigned char *key_data_ptr);
    void Prepare_Key_8bytes(const unsigned char *key_data_ptr);
 
    struct RC4Key
    {      
        unsigned char State[256];       
        unsigned char X;        
        unsigned char Y;
    };
 
    RC4Key  Key;
};
 
#endif