CHG: minor change initializing array.

[proxmark3-svn] / client / nonce2key / crapto1.c

/*  crapto1.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>

#if !defined LOWMEM && defined __GNUC__
uint8_t filterlut[1 << 20];
static void __attribute__((constructor)) fill_lut()
{
        uint32_t x;
        uint32_t f;
        for(x = 0; x < 1 << 20; ++x) {
                f  = 0xf22c0 >> (x       & 0xf) & 16;
                f |= 0x6c9c0 >> (x >>  4 & 0xf) &  8;
                f |= 0x3c8b0 >> (x >>  8 & 0xf) &  4;
                f |= 0x1e458 >> (x >> 12 & 0xf) &  2;
                f |= 0x0d938 >> (x >> 16 & 0xf) &  1;
                filterlut[x] = BIT(0xEC57E80A, f);
        }
}
#endif



typedef struct bucket {
        uint32_t *head;
        uint32_t *bp;
} bucket_t;

typedef bucket_t bucket_array_t[2][0x100];

typedef struct bucket_info {
        struct {
                uint32_t *head, *tail;
                } bucket_info[2][0x100];
                uint32_t numbuckets;
        } bucket_info_t;


static void bucket_sort_intersect(uint32_t* const estart, uint32_t* const estop,
                                                                  uint32_t* const ostart, uint32_t* const ostop,
                                                                  bucket_info_t *bucket_info, bucket_array_t bucket)
{
        uint32_t *p1, *p2;
        uint32_t *start[2];
        uint32_t *stop[2];

        start[0] = estart;
        stop[0] = estop;
        start[1] = ostart;
        stop[1] = ostop;

        // init buckets to be empty
        for (uint32_t i = 0; i < 2; i++) {
                for (uint32_t j = 0x00; j <= 0xff; j++) {
                        bucket[i][j].bp = bucket[i][j].head;
                }
        }

        // sort the lists into the buckets based on the MSB (contribution bits)
        for (uint32_t i = 0; i < 2; i++) {
                for (p1 = start[i]; p1 <= stop[i]; p1++) {
                        uint32_t bucket_index = (*p1 & 0xff000000) >> 24;
                        *(bucket[i][bucket_index].bp++) = *p1;
                }
        }


        // write back intersecting buckets as sorted list.
        // fill in bucket_info with head and tail of the bucket contents in the list and number of non-empty buckets.
        uint32_t nonempty_bucket;
        for (uint32_t i = 0; i < 2; i++) {
                p1 = start[i];
                nonempty_bucket = 0;
                for (uint32_t j = 0x00; j <= 0xff; j++) {
                        if (bucket[0][j].bp != bucket[0][j].head && bucket[1][j].bp != bucket[1][j].head) { // non-empty intersecting buckets only
                                bucket_info->bucket_info[i][nonempty_bucket].head = p1;
                                for (p2 = bucket[i][j].head; p2 < bucket[i][j].bp; *p1++ = *p2++);
                                bucket_info->bucket_info[i][nonempty_bucket].tail = p1 - 1;
                                nonempty_bucket++;
                        }
                }
                bucket_info->numbuckets = nonempty_bucket;
                }
}

/** binsearch
 * Binary search for the first occurence of *stop's MSB in sorted [start,stop]
 */
static inline uint32_t*
binsearch(uint32_t *start, uint32_t *stop)
{
        uint32_t mid, val = *stop & 0xff000000;
        while(start != stop)
                if(start[mid = (stop - start) >> 1] > val)
                        stop = &start[mid];
                else
                        start += mid + 1;

        return start;
}

/** update_contribution
 * helper, calculates the partial linear feedback contributions and puts in MSB
 */
static inline void
update_contribution(uint32_t *item, const uint32_t mask1, const uint32_t mask2)
{
        uint32_t p = *item >> 25;

        p = p << 1 | parity(*item & mask1);
        p = p << 1 | parity(*item & mask2);
        *item = p << 24 | (*item & 0xffffff);
}

/** extend_table
 * using a bit of the keystream extend the table of possible lfsr states
 */
static inline void
extend_table(uint32_t *tbl, uint32_t **end, int bit, int m1, int m2, uint32_t in)
{
        in <<= 24;

        for(uint32_t *p = tbl; p <= *end; p++) {
                *p <<= 1;
                if(filter(*p) != filter(*p | 1)) {                              // replace
                        *p |= filter(*p) ^ bit;
                        update_contribution(p, m1, m2);
                        *p ^= in;
                } else if(filter(*p) == bit) {                                  // insert
                        *++*end = p[1];
                        p[1] = p[0] | 1;
                        update_contribution(p, m1, m2);
                        *p++ ^= in;
                        update_contribution(p, m1, m2);
                        *p ^= in;
                } else {                                                                                // drop
                        *p-- = *(*end)--;
        }
        }

}


/** extend_table_simple
 * using a bit of the keystream extend the table of possible lfsr states
 */
static inline void
extend_table_simple(uint32_t *tbl, uint32_t **end, int bit)
{
        for(*tbl <<= 1; tbl <= *end; *++tbl <<= 1)
                if(filter(*tbl) ^ filter(*tbl | 1)) {   // replace
                        *tbl |= filter(*tbl) ^ bit;
                } else if(filter(*tbl) == bit) {                // insert
                        *++*end = *++tbl;
                        *tbl = tbl[-1] | 1;
                } else                                                                  // drop
                        *tbl-- = *(*end)--;
}


/** recover
 * recursively narrow down the search space, 4 bits of keystream at a time
 */
static struct Crypto1State*
recover(uint32_t *o_head, uint32_t *o_tail, uint32_t oks,
        uint32_t *e_head, uint32_t *e_tail, uint32_t eks, int rem,
        struct Crypto1State *sl, uint32_t in, bucket_array_t bucket)
{
        uint32_t *o, *e;
        bucket_info_t bucket_info;

        if(rem == -1) {
                for(e = e_head; e <= e_tail; ++e) {
                        *e = *e << 1 ^ parity(*e & LF_POLY_EVEN) ^ !!(in & 4);
                        for(o = o_head; o <= o_tail; ++o, ++sl) {
                                sl->even = *o;
                                sl->odd = *e ^ parity(*o & LF_POLY_ODD);
                        }
                }
                sl->odd = sl->even = 0;
                return sl;
        }

        for(uint32_t i = 0; i < 4 && rem--; i++) {
                extend_table(o_head, &o_tail, (oks >>= 1) & 1,
                        LF_POLY_EVEN << 1 | 1, LF_POLY_ODD << 1, 0);
                if(o_head > o_tail)
                        return sl;

                extend_table(e_head, &e_tail, (eks >>= 1) & 1,
                        LF_POLY_ODD, LF_POLY_EVEN << 1 | 1, (in >>= 2) & 3);
                if(e_head > e_tail)
                        return sl;
        }

        bucket_sort_intersect(e_head, e_tail, o_head, o_tail, &bucket_info, bucket);

        for (int i = bucket_info.numbuckets - 1; i >= 0; i--) {
                sl = recover(bucket_info.bucket_info[1][i].head, bucket_info.bucket_info[1][i].tail, oks,
                                     bucket_info.bucket_info[0][i].head, bucket_info.bucket_info[0][i].tail, eks,
                                         rem, sl, in, bucket);
        }

        return sl;
}
/** lfsr_recovery
 * recover the state of the lfsr given 32 bits of the keystream
 * additionally you can use the in parameter to specify the value
 * that was fed into the lfsr at the time the keystream was generated
 */
struct Crypto1State* lfsr_recovery32(uint32_t ks2, uint32_t in)
{
        struct Crypto1State *statelist;
        uint32_t *odd_head = 0, *odd_tail = 0, oks = 0;
        uint32_t *even_head = 0, *even_tail = 0, eks = 0;
        int i;

        // split the keystream into an odd and even part
        for(i = 31; i >= 0; i -= 2)
                oks = oks << 1 | BEBIT(ks2, i);
        for(i = 30; i >= 0; i -= 2)
                eks = eks << 1 | BEBIT(ks2, i);

        odd_head = odd_tail = malloc(sizeof(uint32_t) << 21);
        even_head = even_tail = malloc(sizeof(uint32_t) << 21);
        statelist =  malloc(sizeof(struct Crypto1State) << 18);
        if(!odd_tail-- || !even_tail-- || !statelist) {
                goto out;
        }
        statelist->odd = statelist->even = 0;

        // allocate memory for out of place bucket_sort
        bucket_array_t bucket;
        for (uint32_t i = 0; i < 2; i++)
                for (uint32_t j = 0; j <= 0xff; j++) {
                        bucket[i][j].head = malloc(sizeof(uint32_t)<<14);
                        if (!bucket[i][j].head) {
                                goto out;
                        }
                }

        // initialize statelists: add all possible states which would result into the rightmost 2 bits of the keystream
        for(i = 1 << 20; i >= 0; --i) {
                if(filter(i) == (oks & 1))
                        *++odd_tail = i;
                if(filter(i) == (eks & 1))
                        *++even_tail = i;
        }

        // extend the statelists. Look at the next 8 Bits of the keystream (4 Bit each odd and even):
        for(i = 0; i < 4; i++) {
                extend_table_simple(odd_head,  &odd_tail, (oks >>= 1) & 1);
                extend_table_simple(even_head, &even_tail, (eks >>= 1) & 1);
        }

        // the statelists now contain all states which could have generated the last 10 Bits of the keystream.
        // 22 bits to go to recover 32 bits in total. From now on, we need to take the "in"
        // parameter into account.

        in = (in >> 16 & 0xff) | (in << 16) | (in & 0xff00);            // Byte swapping

        recover(odd_head, odd_tail, oks, even_head, even_tail, eks, 11, statelist, in << 1, bucket);

out:
        free(odd_head);
        free(even_head);
        for (uint32_t i = 0; i < 2; i++)
                for (uint32_t j = 0; j <= 0xff; j++)
                        free(bucket[i][j].head);

        return statelist;
}

static const uint32_t S1[] = {     0x62141, 0x310A0, 0x18850, 0x0C428, 0x06214,
        0x0310A, 0x85E30, 0xC69AD, 0x634D6, 0xB5CDE, 0xDE8DA, 0x6F46D, 0xB3C83,
        0x59E41, 0xA8995, 0xD027F, 0x6813F, 0x3409F, 0x9E6FA};
static const uint32_t S2[] = {  0x3A557B00, 0x5D2ABD80, 0x2E955EC0, 0x174AAF60,
        0x0BA557B0, 0x05D2ABD8, 0x0449DE68, 0x048464B0, 0x42423258, 0x278192A8,
        0x156042D0, 0x0AB02168, 0x43F89B30, 0x61FC4D98, 0x765EAD48, 0x7D8FDD20,
        0x7EC7EE90, 0x7F63F748, 0x79117020};
static const uint32_t T1[] = {
        0x4F37D, 0x279BE, 0x97A6A, 0x4BD35, 0x25E9A, 0x12F4D, 0x097A6, 0x80D66,
        0xC4006, 0x62003, 0xB56B4, 0x5AB5A, 0xA9318, 0xD0F39, 0x6879C, 0xB057B,
        0x582BD, 0x2C15E, 0x160AF, 0x8F6E2, 0xC3DC4, 0xE5857, 0x72C2B, 0x39615,
        0x98DBF, 0xC806A, 0xE0680, 0x70340, 0x381A0, 0x98665, 0x4C332, 0xA272C};
static const uint32_t T2[] = {  0x3C88B810, 0x5E445C08, 0x2982A580, 0x14C152C0,
        0x4A60A960, 0x253054B0, 0x52982A58, 0x2FEC9EA8, 0x1156C4D0, 0x08AB6268,
        0x42F53AB0, 0x217A9D58, 0x161DC528, 0x0DAE6910, 0x46D73488, 0x25CB11C0,
        0x52E588E0, 0x6972C470, 0x34B96238, 0x5CFC3A98, 0x28DE96C8, 0x12CFC0E0,
        0x4967E070, 0x64B3F038, 0x74F97398, 0x7CDC3248, 0x38CE92A0, 0x1C674950,
        0x0E33A4A8, 0x01B959D0, 0x40DCACE8, 0x26CEDDF0};
static const uint32_t C1[] = { 0x846B5, 0x4235A, 0x211AD};
static const uint32_t C2[] = { 0x1A822E0, 0x21A822E0, 0x21A822E0};
/** Reverse 64 bits of keystream into possible cipher states
 * Variation mentioned in the paper. Somewhat optimized version
 */
struct Crypto1State* lfsr_recovery64(uint32_t ks2, uint32_t ks3)
{
        struct Crypto1State *statelist, *sl;
        uint8_t oks[32], eks[32], hi[32];
        uint32_t low = 0,  win = 0;
        uint32_t *tail, table[1 << 16];
        int i, j;

        sl = statelist = malloc(sizeof(struct Crypto1State) << 4);
        if(!sl)
                return 0;
        sl->odd = sl->even = 0;

        for(i = 30; i >= 0; i -= 2) {
                oks[i >> 1] = BIT(ks2, i ^ 24);
                oks[16 + (i >> 1)] = BIT(ks3, i ^ 24);
        }
        for(i = 31; i >= 0; i -= 2) {
                eks[i >> 1] = BIT(ks2, i ^ 24);
                eks[16 + (i >> 1)] = BIT(ks3, i ^ 24);
        }

        for(i = 0xfffff; i >= 0; --i) {
                if (filter(i) != oks[0])
                        continue;

                *(tail = table) = i;
                for(j = 1; tail >= table && j < 29; ++j)
                        extend_table_simple(table, &tail, oks[j]);

                if(tail < table)
                        continue;

                for(j = 0; j < 19; ++j)
                        low = low << 1 | parity(i & S1[j]);
                for(j = 0; j < 32; ++j)
                        hi[j] = parity(i & T1[j]);

                for(; tail >= table; --tail) {
                        for(j = 0; j < 3; ++j) {
                                *tail = *tail << 1;
                                *tail |= parity((i & C1[j]) ^ (*tail & C2[j]));
                                if(filter(*tail) != oks[29 + j])
                                        goto continue2;
                        }

                        for(j = 0; j < 19; ++j)
                                win = win << 1 | parity(*tail & S2[j]);

                        win ^= low;
                        for(j = 0; j < 32; ++j) {
                                win = win << 1 ^ hi[j] ^ parity(*tail & T2[j]);
                                if(filter(win) != eks[j])
                                        goto continue2;
                        }

                        *tail = *tail << 1 | parity(LF_POLY_EVEN & *tail);
                        sl->odd = *tail ^ parity(LF_POLY_ODD & win);
                        sl->even = win;
                        ++sl;
                        sl->odd = sl->even = 0;
                        continue2:;
                }
        }
        return statelist;
}

/** lfsr_rollback_bit
 * Rollback the shift register in order to get previous states
 */
void lfsr_rollback_bit(struct Crypto1State *s, uint32_t in, int fb)
{
        int out;
        uint32_t tmp;

        s->odd &= 0xffffff;
        tmp = s->odd;
        s->odd = s->even;
        s->even = tmp;

        out = s->even & 1;
        out ^= LF_POLY_EVEN & (s->even >>= 1);
        out ^= LF_POLY_ODD & s->odd;
        out ^= !!in;
        out ^= filter(s->odd) & !!fb;

        s->even |= parity(out) << 23;
}
/** lfsr_rollback_byte
 * Rollback the shift register in order to get previous states
 */
void lfsr_rollback_byte(struct Crypto1State *s, uint32_t in, int fb)
{
/*      int i;
        for (i = 7; i >= 0; --i)
                lfsr_rollback_bit(s, BEBIT(in, i), fb);
*/
// unfold loop 20160112
        lfsr_rollback_bit(s, BEBIT(in, 7), fb);
        lfsr_rollback_bit(s, BEBIT(in, 6), fb);
        lfsr_rollback_bit(s, BEBIT(in, 5), fb);
        lfsr_rollback_bit(s, BEBIT(in, 4), fb);
        lfsr_rollback_bit(s, BEBIT(in, 3), fb);
        lfsr_rollback_bit(s, BEBIT(in, 2), fb);
        lfsr_rollback_bit(s, BEBIT(in, 1), fb);
        lfsr_rollback_bit(s, BEBIT(in, 0), fb);
}
/** lfsr_rollback_word
 * Rollback the shift register in order to get previous states
 */
void lfsr_rollback_word(struct Crypto1State *s, uint32_t in, int fb)
{
/*
        int i;
        for (i = 31; i >= 0; --i)
                lfsr_rollback_bit(s, BEBIT(in, i), fb);
*/
// unfold loop 20160112
        lfsr_rollback_bit(s, BEBIT(in, 31), fb);
        lfsr_rollback_bit(s, BEBIT(in, 30), fb);
        lfsr_rollback_bit(s, BEBIT(in, 29), fb);
        lfsr_rollback_bit(s, BEBIT(in, 28), fb);
        lfsr_rollback_bit(s, BEBIT(in, 27), fb);
        lfsr_rollback_bit(s, BEBIT(in, 26), fb);
        lfsr_rollback_bit(s, BEBIT(in, 25), fb);
        lfsr_rollback_bit(s, BEBIT(in, 24), fb);

        lfsr_rollback_bit(s, BEBIT(in, 23), fb);
        lfsr_rollback_bit(s, BEBIT(in, 22), fb);
        lfsr_rollback_bit(s, BEBIT(in, 21), fb);
        lfsr_rollback_bit(s, BEBIT(in, 20), fb);
        lfsr_rollback_bit(s, BEBIT(in, 19), fb);
        lfsr_rollback_bit(s, BEBIT(in, 18), fb);
        lfsr_rollback_bit(s, BEBIT(in, 17), fb);
        lfsr_rollback_bit(s, BEBIT(in, 16), fb);

        lfsr_rollback_bit(s, BEBIT(in, 15), fb);
        lfsr_rollback_bit(s, BEBIT(in, 14), fb);
        lfsr_rollback_bit(s, BEBIT(in, 13), fb);
        lfsr_rollback_bit(s, BEBIT(in, 12), fb);
        lfsr_rollback_bit(s, BEBIT(in, 11), fb);
        lfsr_rollback_bit(s, BEBIT(in, 10), fb);
        lfsr_rollback_bit(s, BEBIT(in, 9), fb);
        lfsr_rollback_bit(s, BEBIT(in, 8), fb);

        lfsr_rollback_bit(s, BEBIT(in, 7), fb);
        lfsr_rollback_bit(s, BEBIT(in, 6), fb);
        lfsr_rollback_bit(s, BEBIT(in, 5), fb);
        lfsr_rollback_bit(s, BEBIT(in, 4), fb);
        lfsr_rollback_bit(s, BEBIT(in, 3), fb);
        lfsr_rollback_bit(s, BEBIT(in, 2), fb);
        lfsr_rollback_bit(s, BEBIT(in, 1), fb);
        lfsr_rollback_bit(s, BEBIT(in, 0), fb);
}

/** nonce_distance
 * x,y valid tag nonces, then prng_successor(x, nonce_distance(x, y)) = y
 */
static uint16_t *dist = 0;
int nonce_distance(uint32_t from, uint32_t to)
{
        uint16_t x, i;
        if(!dist) {
                dist = malloc(2 << 16);
                if(!dist)
                        return -1;
                for (x = i = 1; i; ++i) {
                        dist[(x & 0xff) << 8 | x >> 8] = i;
                        x = x >> 1 | (x ^ x >> 2 ^ x >> 3 ^ x >> 5) << 15;
                }
        }
        return (65535 + dist[to >> 16] - dist[from >> 16]) % 65535;
}


static uint32_t fastfwd[2][8] = {
        { 0, 0x4BC53, 0xECB1, 0x450E2, 0x25E29, 0x6E27A, 0x2B298, 0x60ECB},
        { 0, 0x1D962, 0x4BC53, 0x56531, 0xECB1, 0x135D3, 0x450E2, 0x58980}};


/** lfsr_prefix_ks
 *
 * Is an exported helper function from the common prefix attack
 * Described in the "dark side" paper. It returns an -1 terminated array
 * of possible partial(21 bit) secret state.
 * The required keystream(ks) needs to contain the keystream that was used to
 * encrypt the NACK which is observed when varying only the 4 last bits of Nr
 * only correct iff [NR_3] ^ NR_3 does not depend on Nr_3
 */
uint32_t *lfsr_prefix_ks(uint8_t ks[8], int isodd)
{
        uint32_t *candidates = malloc(4 << 21);
        uint32_t c,  entry;
        int size, i;

        if(!candidates)
                return 0;

        size = (1 << 21) - 1;
        for(i = 0; i <= size; ++i)
                candidates[i] = i;

        for(c = 0;  c < 8; ++c)
                for(i = 0;i <= size; ++i) {
                        entry = candidates[i] ^ fastfwd[isodd][c];

                        if(filter(entry >> 1) == BIT(ks[c], isodd))
                                if(filter(entry) == BIT(ks[c], isodd + 2))
                                        continue;

                        candidates[i--] = candidates[size--];
                }

        candidates[size + 1] = -1;

        return candidates;
}

/** brute_top
 * helper function which eliminates possible secret states using parity bits
 */
static struct Crypto1State*
brute_top(uint32_t prefix, uint32_t rresp, unsigned char parities[8][8],
          uint32_t odd, uint32_t even, struct Crypto1State* sl, uint8_t no_chk)
{
        struct Crypto1State s;
        uint32_t ks1, nr, ks2, rr, ks3, good, c;

        for(c = 0; c < 8; ++c) {
                s.odd = odd ^ fastfwd[1][c];
                s.even = even ^ fastfwd[0][c];

                lfsr_rollback_bit(&s, 0, 0);
                lfsr_rollback_bit(&s, 0, 0);
                lfsr_rollback_bit(&s, 0, 0);

                lfsr_rollback_word(&s, 0, 0);
                lfsr_rollback_word(&s, prefix | c << 5, 1);

                sl->odd = s.odd;
                sl->even = s.even;

                if (no_chk)
                        break;

                ks1 = crypto1_word(&s, prefix | c << 5, 1);
                ks2 = crypto1_word(&s,0,0);
                ks3 = crypto1_word(&s, 0,0);
                nr = ks1 ^ (prefix | c << 5);
                rr = ks2 ^ rresp;

                good = 1;
                good &= parity(nr & 0x000000ff) ^ parities[c][3] ^ BIT(ks2, 24);
                good &= parity(rr & 0xff000000) ^ parities[c][4] ^ BIT(ks2, 16);
                good &= parity(rr & 0x00ff0000) ^ parities[c][5] ^ BIT(ks2,  8);
                good &= parity(rr & 0x0000ff00) ^ parities[c][6] ^ BIT(ks2,  0);
                good &= parity(rr & 0x000000ff) ^ parities[c][7] ^ BIT(ks3, 24);

                if(!good)
                        return sl;
        }

        return ++sl;
}


/** lfsr_common_prefix
 * Implentation of the common prefix attack.
 * Requires the 28 bit constant prefix used as reader nonce (pfx)
 * The reader response used (rr)
 * The keystream used to encrypt the observed NACK's (ks)
 * The parity bits (par)
 * It returns a zero terminated list of possible cipher states after the
 * tag nonce was fed in
 */
struct Crypto1State* lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8], uint8_t no_par)
{
        struct Crypto1State *statelist, *s;
        uint32_t *odd, *even, *o, *e, top;

        odd = lfsr_prefix_ks(ks, 1);
        even = lfsr_prefix_ks(ks, 0);

        statelist = malloc((sizeof *statelist) << 21);  //how large should be?
        if(!statelist || !odd || !even)
        {
                free(statelist);
                free(odd);
                free(even);
                return 0;
        }

        s = statelist;
        for(o = odd; *o != -1; ++o)
                for(e = even; *e != -1; ++e)
                        for(top = 0; top < 64; ++top) {
                                *o = (*o & 0x1fffff) | (top << 21);
                                *e = (*e & 0x1fffff) | (top >> 3) << 21;
                                s = brute_top(pfx, rr, par, *o, *e, s, no_par);
                        }

        s->odd = s->even = -1;
        //printf("state count = %d\n",s-statelist);

        free(odd);
        free(even);

        return statelist;
}

/*
struct Crypto1State* lfsr_common_prefix(uint32_t pfx, uint32_t rr, uint8_t ks[8], uint8_t par[8][8], uint8_t no_par, uint32_t nt, uint32_t uid)
{
    long long int amount = 0;
    struct Crypto1State *statelist, *s;
    uint32_t *odd, *even, *o, *e, top;

    odd = lfsr_prefix_ks(ks, 1);
    even = lfsr_prefix_ks(ks, 0);

    s = statelist = malloc((sizeof *statelist) << 20);
    if(!s || !odd || !even) {
                free(odd);
                free(even);
                free(statelist);
                return 0;
    }

    char filename[50] = "archivo.txt";
    sprintf(filename, "logs/%x.txt", nt);
    PrintAndLog("Name: %s\n", filename);
    FILE *file = fopen(filename,"w+");
        if ( !file ) {
                s->odd = s->even = 0;
                free(odd);
                free(even);
                PrintAndLog("Failed to create file");
                return 0;
        }
    PrintAndLog("Creating file... ");
        uint32_t xored = uid^nt;
        
    int lastOdd = 0;
    for(o = odd; *o + 1; ++o)
        for(e = even; *e + 1; ++e)
            for(top = 0; top < 64; ++top) {
                *o += 1 << 21;
                *e += (!(top & 7) + 1) << 21;

                //added by MG
                if(lastOdd != statelist->odd){
                                        // Here I create a temporal crypto1 state, 
                                        // where I load the odd and even state and work with it,
                                        // in order not to interfere with regular mechanism, This is what I save to file
                                        struct Crypto1State *state;
                    lastOdd = state->odd = statelist->odd; state->even = statelist->even;
                    lfsr_rollback_word(state,xored,0);
                    fprintf(file,"%x %x \n",state->odd,state->even);
                    amount++;
                }
                //s = check_pfx_parity(pfx, rr, par, *o, *e, s); //This is not useful at all when attacking chineese cards
                                s = brute_top(pfx, rr, par, *o, *e, s, no_par); 
            }

        PrintAndLog("File created, amount %u\n",amount);
        fclose(file);
        s->odd = s->even = 0;
        free(odd);
        free(even);
    return statelist;
}
 */