/* modes.hpp                                
 *
 * Copyright (C) 2003 Sawtooth Consulting Ltd.
 *
 * This file is part of yaSSL.
 *
 * yaSSL 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 2 of the License, or
 * (at your option) any later version.
 *
 * There are special exceptions to the terms and conditions of the GPL as it
 * is applied to yaSSL. View the full text of the exception in the file
 * FLOSS-EXCEPTIONS in the directory of this software distribution.
 *
 * yaSSL 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

/* modes.hpp provides ECB and CBC modes for block cipher encryption/decryption
*/


#ifndef TAO_CRYPT_MODES_HPP
#define TAO_CRYPT_MODES_HPP

#include "misc.hpp"

namespace TaoCrypt {


enum Mode { ECB, CBC };



// BlockCipher abstraction
template<CipherDir DIR, class T, Mode MODE>
class BlockCipher {
public:
    BlockCipher() : cipher_(DIR, MODE) {}

    void Process(byte* c, const byte* p, word32 sz) 
            { cipher_.Process(c, p, sz); }
    void SetKey(const byte* k, word32 sz)   
            { cipher_.SetKey(k, sz, DIR); }
    void SetKey(const byte* k, word32 sz, const byte* iv)   
            { cipher_.SetKey(k, sz, DIR); cipher_.SetIV(iv); }
private:
    T cipher_;

    BlockCipher(const BlockCipher&);            // hide copy
    BlockCipher& operator=(const BlockCipher&); // and assign
};


// Mode Base for block ciphers, static size
class Mode_BASE : public virtual_base {
public:
    enum { MaxBlockSz = 16 };

    explicit Mode_BASE(int sz, CipherDir dir, Mode mode) 
        : blockSz_(sz), reg_(reinterpret_cast<byte*>(r_)),
          tmp_(reinterpret_cast<byte*>(t_)), dir_(dir), mode_(mode)
    { 
        assert(sz <= MaxBlockSz);
    }
    virtual ~Mode_BASE() {}

    virtual void Process(byte*, const byte*, word32);

    void SetIV(const byte* iv) { memcpy(reg_, iv, blockSz_); }
protected:
    int   blockSz_;
    byte* reg_;
    byte* tmp_;

    word32 r_[MaxBlockSz / sizeof(word32)];  // align reg_ on word32
    word32 t_[MaxBlockSz / sizeof(word32)];  // align tmp_ on word32

    CipherDir dir_;
    Mode      mode_;

    void ECB_Process(byte*, const byte*, word32);
    void CBC_Encrypt(byte*, const byte*, word32);
    void CBC_Decrypt(byte*, const byte*, word32);

    Mode_BASE(const Mode_BASE&);            // hide copy
    Mode_BASE& operator=(const Mode_BASE&); // and assign

private:
    virtual void ProcessAndXorBlock(const byte*, const byte*, byte*) const = 0;
};


inline void Mode_BASE::Process(byte* out, const byte* in, word32 sz)
{
    if (mode_ == ECB)
        ECB_Process(out, in, sz);
    else if (mode_ == CBC)
        if (dir_ == ENCRYPTION)
            CBC_Encrypt(out, in, sz);
        else
            CBC_Decrypt(out, in, sz);
}


// ECB Process blocks
inline void Mode_BASE::ECB_Process(byte* out, const byte* in, word32 sz)
{
    word32 blocks = sz / blockSz_;

    while (blocks--) {
        ProcessAndXorBlock(in, 0, out);
        out += blockSz_;
        in  += blockSz_;
    }
}


// CBC Encrypt
inline void Mode_BASE::CBC_Encrypt(byte* out, const byte* in, word32 sz)
{
    word32 blocks = sz / blockSz_;

    while (blocks--) {
        xorbuf(reg_, in, blockSz_);
        ProcessAndXorBlock(reg_, 0, reg_);
        memcpy(out, reg_, blockSz_);
        out += blockSz_;
        in  += blockSz_;
    }
}


// CBC Decrypt
inline void Mode_BASE::CBC_Decrypt(byte* out, const byte* in, word32 sz)
{
    word32 blocks = sz / blockSz_;
    byte   hold[MaxBlockSz];

    while (blocks--) {
        memcpy(tmp_, in, blockSz_);
        ProcessAndXorBlock(tmp_, 0, out);
        xorbuf(out,  reg_, blockSz_);
        memcpy(hold, reg_,   blockSz_); // swap reg_ and tmp_
        memcpy(reg_,   tmp_, blockSz_);
        memcpy(tmp_, hold, blockSz_);
        out += blockSz_;
        in  += blockSz_;
    }
}


} // namespace

#endif  // TAO_CRYPT_MODES_HPP
