avr-crypto-lib/cscipher/cscipher_small.c

/* cscipher_small_core.c */
/*
 This file is part of the ARM-Crypto-Lib.
 Copyright (C) 2006-2015 Daniel Otte (bg@nerilex.org)

 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/>.
 */

#include <stdint.h>
#include <avr/pgmspace.h>
#include <stdlib.h>
#include <string.h>
#include "memxor.h"
#include "cscipher.h"

#define DEBUG 0

#if DEBUG
#include "cli.h"
#endif

#define ROTL(a) (((a)<<1)|((a)>>7))

#ifndef SBOX_PROG
#define SBOX_PROG 0
#endif

#if SBOX_PROG
static const uint8_t fg_table[] PROGMEM = {
    0xfa, 0xd6, 0xb0, 0xb2, 0x7b, 0x5e, 0x71, 0x78,
    0xed, 0xd4, 0xa5, 0xb3, 0xef, 0xdc, 0xe7, 0xf9
};

static
uint8_t p(uint8_t a) {
    a ^= pgm_read_byte(fg_table+(a&0xf))&0xf0;
    a ^= pgm_read_byte(fg_table+(a>>4)) &0x0f;
    a ^= pgm_read_byte(fg_table+(a&0xf))&0xf0;
    return a;
}
#define P(a) p(a)

#else

#include "cscipher_sbox.h"
#define P(a) pgm_read_byte(cscipher_sbox+(a))
#endif

static const uint8_t round_const[] PROGMEM = {
        0xb7, 0xe1, 0x51, 0x62, 0x8a, 0xed, 0x2a, 0x6a,
        0xbf, 0x71, 0x58, 0x80, 0x9c, 0xf4, 0xf3, 0xc7 };

static const uint8_t ks_const[] PROGMEM = {
        0x29, 0x0d, 0x61, 0x40, 0x9c, 0xeb, 0x9e, 0x8f,
        0x1f, 0x85, 0x5f, 0x58, 0x5b, 0x01, 0x39, 0x86,
        0x97, 0x2e, 0xd7, 0xd6, 0x35, 0xae, 0x17, 0x16,
        0x21, 0xb6, 0x69, 0x4e, 0xa5, 0x72, 0x87, 0x08,
        0x3c, 0x18, 0xe6, 0xe7, 0xfa, 0xad, 0xb8, 0x89,
        0xb7, 0x00, 0xf7, 0x6f, 0x73, 0x84, 0x11, 0x63,
        0x3f, 0x96, 0x7f, 0x6e, 0xbf, 0x14, 0x9d, 0xac,
        0xa4, 0x0e, 0x7e, 0xf6, 0x20, 0x4a, 0x62, 0x30,
        0x03, 0xc5, 0x4b, 0x5a, 0x46, 0xa3, 0x44, 0x65
};

static uint16_t m(uint16_t a)
{
    uint8_t xl, xr, yl, yr;
    uint16_t ret;
    xr = a >> 8;
    xl = a & 0xff;
    yl = (ROTL(xl) & 0x55) ^ xl ^ xr;
    yr = ROTL(xl) ^ xr;
    ret = (P(yr) << 8) | P(yl);
    return ret;
}

static uint16_t m_inv(uint16_t a)
{
    uint8_t xl, xr;
    xr = P(a >> 8);
    xl = P(a & 0xff);
    xl ^= xr;
    xl ^= (ROTL(xl) & 0xaa);
    xr ^= ROTL(xl);
    return (xr << 8) | xl;
}

void cscipher_enc(void *buffer, const cscipher_ctx_t *ctx)
{
    uint8_t i, j, k;
    uint8_t tmp[8];
    for (i = 0; i < 8; ++i) {
#if DEBUG
        cli_putstr_P(PSTR("\r\nDBG: round "));
        cli_hexdump(&i, 1);
        cli_putstr_P(PSTR(" buffer:"));
        cli_hexdump(buffer, 8);
#endif
        for (j = 0; j < 3; ++j) {
            if (j == 0) {
                memxor(buffer, ctx->keys[i], 8);
            } else {
                memxor_P(buffer, round_const + ((j == 1) ? 0 : 8), 8);
            }
            for (k = 0; k < 4; ++k) {
                ((uint16_t*) tmp)[k] = m(((uint16_t*) buffer)[k]);
            }
            for (k = 0; k < 4; ++k) {
                ((uint8_t*) buffer)[k] = tmp[2 * k];
                ((uint8_t*) buffer)[k + 4] = tmp[2 * k + 1];
            }
        }
    }
    memxor(buffer, ctx->keys[8], 8);
}

void cscipher_dec(void *buffer, const cscipher_ctx_t *ctx)
{
    uint8_t i = 7, j, k;
    uint8_t tmp[8];
    memxor(buffer, ctx->keys[8], 8);
    do {
        for (j = 0; j < 3; ++j) {
            for (k = 0; k < 4; ++k) {
                tmp[2 * k] = ((uint8_t*) buffer)[k];
                tmp[2 * k + 1] = ((uint8_t*) buffer)[4 + k];
            }
            for (k = 0; k < 4; ++k) {
                ((uint16_t*) buffer)[k] = m_inv(((uint16_t*) tmp)[k]);
            }
            if (j == 2) {
                memxor(buffer, ctx->keys[i], 8);
            } else {
                memxor_P(buffer, round_const + ((j == 1) ? 0 : 8), 8);
            }

        }
    } while (i--);
}

void cscipher_init(const void *key, cscipher_ctx_t *ctx)
{
    uint8_t tmp_key[16], tmp[8];
    uint8_t i, j, k, t = 0;
    memcpy(tmp_key, key, 16);
    for (i = 0; i < 9; ++i) {
#if DEBUG
        cli_putstr_P(PSTR("\r\nDBG: round "));
        cli_hexdump(&i, 1);
        cli_putstr_P(PSTR(" key state:"));
        cli_hexdump(tmp_key, 16);
#endif
        memcpy(tmp, tmp_key + (((i & 1) == 0) ? 0 : 8), 8);
        memxor_P(tmp, ks_const + 8 * i, 8);
        for (j = 0; j < 8; ++j) {
            tmp[j] = P(tmp[j]);
        }
        for (j = 0; j < 8; ++j) {
            for (k = 0; k < 8; ++k) {
                t <<= 1;
                t |= tmp[k] >> 7;
                tmp[k] <<= 1;
            }
            tmp_key[j + (((i & 1) == 0) ? 8 : 0)] ^= t;
        }
        memcpy(ctx->keys[i], tmp_key + (((i & 1) == 0) ? 8 : 0), 8);
    }
}