/*  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(DWORD64 key)
{
    struct Crypto1State *s = (Crypto1State *)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, DWORD64 *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);
    }
}

BYTE crypto1_bit(struct Crypto1State *s, BYTE in, int is_encrypted)
{
    DWORD feedin;
    BYTE 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;
}

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

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

    return ret;
}

DWORD crypto1_word(struct Crypto1State *s, DWORD in, int is_encrypted)
{
    DWORD 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
DWORD prng_successor(DWORD x, DWORD n)
{
    SWAPENDIAN(x);
    while (n--)
        x = x >> 1 | (x >> 16 ^ x >> 18 ^ x >> 19 ^ x >> 21) << 31;

    return SWAPENDIAN(x);
}
