/*****************************************************************************
 *                                                                           *
 *        **********                                                         *
 *       ************                                                        *
 *      ***        ***                                                       *
 *      ***   +++   ***                                                      *
 *      ***   + +   ***                                                      *
 *      ***   +                CHIPCON CC1010 Wireless audio project         *
 *      ***   + +   ***                                                      *
 *      ***   +++   ***          DES - extended version of HAL - DES         *
 *      ***       ***                                                        *
 *       ***********                                                         *
 *        *********                                                          *
 *                                                                           *
 *****************************************************************************
 * This source file is part of a software project for Full Duplex,           *
 * single-chip, wireless intercom, written for the CC1010 chip               *
 * (RF-transceiver chip with integrated 8051 micro-controller).              *
 *****************************************************************************
 * Author:              ROH, (OAE)                                           *
 *****************************************************************************
 * Revision history:                                                         *
 *                                                                           *
 * $Log: DES.c,v $
 * Revision 1.1  2003/08/04 12:35:06  tos
 * Initial version in CVS.
 *
 *                                                                           *
 *                                                                           *
 ****************************************************************************/


#include <chipcon/hal.h>

//----------------------------------------------------------------------------
//  byte* DES(...)
//
//  Description:
//      This function performs DES encryption/decryption on a block of data.
//      The encryption/decryption operations are performed in place (i.e.
//      the plaintext is overwritten by the ciphertext or vice versa) on
//      suitably aligned data [ address(_buffer_) mod 8 = 0 ]. _key_ should 
//      point to the key used for single-DES operations or keys in the case 
//      of triple-DES.
//      Two modes of the DES standard are supported: 8-bit Cipher Feedback
//      (CFB) and Output Feedback (OFB.) CFB is self-synchronizing (the end of
//      a ciphertext can be decrypted even though the beginning is unavailable)
//      and can be used to calculate error check codes. OFB is not self-
//      synchronizing and is not suitable for error check code calculation,
//      but does have the favourable property that a single bit error in the
//      received ciphertext produces only a single bit error in the decrypted
//      plaintext.
//      In CFB/OFB mode an initialization vector of 8 bytes is part of the
//      algorithm. This vector must be identical for the encryption and 
//      decryption process. The choice of initialization data does not affect
//      the security of the encryption in any way, and this function thus uses
//      the value 0.
//      _option_ is used to chose between these modes of operation, between
//      single-DES and triple-DES, and between decryption and decryption.
//      This function does not return until all data has been encrypted/
//      decrypted, since the DES hardware is so fast. The DES hardware can
//      run at the same time as the 8051 and generate an intterrupt when
//      finished. If this is desired the hardware must be programmed directly.
//
//  Arguments:
//      byte options
//          One or more of the below defined constants define the desired
//          operational mode:
//          DES_SINGLE_DES
//          DES_TRIPLE_DES
//          DES_ENCRYPT
//          DES_DECRYPT
//          DES_OFB_MODE
//          DES_CFB_MODE

//      byte xdata* key
//          A pointer to a key (or three keys for triple-DES) stored in
//          XDATA memory space. This address must be divisible by eight, i.e.
//          address(_key_) mod 8 = 0. The 56 active bits of a DES-key are
//          expected to be in a compressed 7-byte format, in which all parity
//          bits are removed. In the case of a single key, the 56 bits of the key
//          must lie on _key_[0] - _key_[6], in big-endian order. In the case of
//          three keys (triple-des), the three keys must lie on _key_[0] -
//          _key_[6], _key_[8] - _key_[14] and _key_[16] - _key_[22], all in big-
//          endian order. The macro DES_NORMAL_2_COMPACT_KEY(...) can be used
//          to convert a regular DES key to the compact form. A key can be
//          generated by simply using 7 random bytes.
//
//      byte xdata* buffer
//          Pointer to the data to encrypt/decrypt in XDATA memory space.
//          Encryption/decryption is performed in-place, i.e. the original
//          plaintext/ciphertext is overwritten. The address of _buffer_ must
//          be divisible by eight, i.e. address(_buffer_) mod 8 = 0.
//      word length
//          The number of bytes to perform the encryption/decryption on.
//      bit wait
//          If this bit is set, the function will wait until encryption/decryption
//          is completed, otherwise the function will return a
//
//  Return value:
//      byte*
//          A pointer to the start of _buffer_ is returned.
//----------------------------------------------------------------------------
byte* DES(byte options, byte xdata* buffer, byte xdata* key, word length, bit wait) {

    CRPCON=0x10|(options&0x0E);         // Init control register
    CRPKEY=((word)key)>>3;              // Put address of key(s) into register
    CRPDAT=((word)buffer)>>3;           // Put address of data into register
    CRPINI7=CRPINI6=CRPINI5=CRPINI4=0;  // Clear initialization vector
    CRPINI3=CRPINI2=CRPINI1=CRPINI0=0;

    while (length) {
        // Encryption/decryption performed in blocks of maximum 256 bytes.
        if (length&0xFF00){    // >=256
            CRPCNT=0;
            length-=256;
        } else {
            CRPCNT=length;
            length=0;
        }
        CRPCON|=0x01;           // Start encryption/decryption

        // Wait until finished if wait bit is set
        if (wait)
            while (CRPCON&0x01);
    }

    return buffer;
}
//----------------------------------------------------------------------------