/*  crypto1.c

    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 2
    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, write to the Free Software
    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
    MA  02110-1301, US

    Copyright (C) 2008-2008 bla <blapost@gmail.com>
*/
#include "crapto1.h"
#include <stdlib.h>

#define SWAPENDIAN(x)\
  (x = (x >> 8 & 0xff00ff) | (x & 0xff00ff) << 8, x = x >> 16 | x << 16)

struct Crypto1State *crypto1_create(uint64_t key) {
  struct Crypto1State *s = malloc(sizeof(*s));
  int i;

  for (i = 47; s && i > 0; i -= 2) {
    s->odd  = s->odd  << 1 | BIT(key, (i - 1) ^ 7);
    s->even = s->even << 1 | BIT(key, i ^ 7);
  }
  return s;
}
void crypto1_destroy(struct Crypto1State *state)
{
  free(state);
}
void crypto1_get_lfsr(struct Crypto1State *state, uint64_t *lfsr)
{
  int i;
  for (*lfsr = 0, i = 23; i >= 0; --i) {
    *lfsr = *lfsr << 1 | BIT(state->odd, i ^ 3);
    *lfsr = *lfsr << 1 | BIT(state->even, i ^ 3);
  }
}
uint8_t crypto1_bit(struct Crypto1State *s, uint8_t in, int is_encrypted)
{
  uint32_t feedin;
  uint8_t ret = filter(s->odd);

  feedin  = ret & !!is_encrypted;
  feedin ^= !!in;
  feedin ^= LF_POLY_ODD & s->odd;
  feedin ^= LF_POLY_EVEN & s->even;
  s->even = s->even << 1 | parity(feedin);

  s->odd ^= (s->odd ^= s->even, s->even ^= s->odd);

  return ret;
}
uint8_t crypto1_byte(struct Crypto1State *s, uint8_t in, int is_encrypted)
{
  uint8_t i, ret = 0;

  for (i = 0; i < 8; ++i)
    ret |= crypto1_bit(s, BIT(in, i), is_encrypted) << i;

  return ret;
}
uint32_t crypto1_word(struct Crypto1State *s, uint32_t in, int is_encrypted)
{
  uint32_t i, ret = 0;

  for (i = 0; i < 32; ++i)
    ret |= crypto1_bit(s, BEBIT(in, i), is_encrypted) << (i ^ 24);

  return ret;
}

/* prng_successor
 * helper used to obscure the keystream during authentication
 */
uint32_t prng_successor(uint32_t x, uint32_t n)
{
  SWAPENDIAN(x);
  while (n--)
    x = x >> 1 | (x >> 16 ^ x >> 18 ^ x >> 19 ^ x >> 21) << 31;

  return SWAPENDIAN(x);
}
