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500 lines
15 KiB
C
500 lines
15 KiB
C
/* reveng.c
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* Greg Cook, 26/Jul/2018
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*/
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/* CRC RevEng: arbitrary-precision CRC calculator and algorithm finder
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* Copyright (C) 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018
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* Gregory Cook
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*
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* This file is part of CRC RevEng.
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*
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* CRC RevEng is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* CRC RevEng is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with CRC RevEng. If not, see <https://www.gnu.org/licenses/>.
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*/
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/* 2013-09-16: calini(), calout() work on shortest argument
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* 2013-06-11: added sequence number to uprog() calls
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* 2013-02-08: added polynomial range search
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* 2013-01-18: refactored model checking to pshres(); renamed chkres()
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* 2012-05-24: efficiently build Init contribution string
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* 2012-05-24: removed broken search for crossed-endian algorithms
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* 2012-05-23: rewrote engini() after Ewing; removed modini()
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* 2011-01-17: fixed ANSI C warnings
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* 2011-01-08: fixed calini(), modini() caters for crossed-endian algos
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* 2011-01-04: renamed functions, added calini(), factored pshres();
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* rewrote engini() and implemented quick Init search
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* 2011-01-01: reveng() initialises terminating entry, addparms()
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* initialises all fields
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* 2010-12-26: renamed CRC RevEng. right results, rejects polys faster
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* 2010-12-24: completed, first tests (unsuccessful)
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* 2010-12-21: completed modulate(), partial sketch of reveng()
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* 2010-12-19: started reveng
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*/
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/* reveng() can in theory be modified to search for polynomials shorter
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* than the full width as well, but this imposes a heavy time burden on
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* the full width search, which is the primary use case, as well as
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* complicating the search range function introduced in version 1.1.0.
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* It is more effective to search for each shorter width directly.
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*/
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#include <stdlib.h>
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#define FILE void
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#include "reveng.h"
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static poly_t *modpol(const poly_t init, int rflags, int args, const poly_t *argpolys);
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static void engini(int *resc, model_t **result, const poly_t divisor, int flags, int args, const poly_t *argpolys);
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static void calout(int *resc, model_t **result, const poly_t divisor, const poly_t init, int flags, int args, const poly_t *argpolys);
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static void calini(int *resc, model_t **result, const poly_t divisor, int flags, const poly_t xorout, int args, const poly_t *argpolys);
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static void chkres(int *resc, model_t **result, const poly_t divisor, const poly_t init, int flags, const poly_t xorout, int args, const poly_t *argpolys);
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static const poly_t pzero = PZERO;
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model_t *
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reveng(const model_t *guess, const poly_t qpoly, int rflags, int args, const poly_t *argpolys) {
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/* Complete the parameters of a model by calculation or brute search. */
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poly_t *pworks, *wptr, rem, gpoly;
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model_t *result = NULL, *rptr;
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int resc = 0;
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unsigned long spin = 0, seq = 0;
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if(~rflags & R_HAVEP) {
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/* The poly is not known.
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* Produce a list of differences between the arguments.
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*/
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pworks = modpol(guess->init, rflags, args, argpolys);
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if(!pworks || !plen(*pworks)) {
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free(pworks);
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goto requit;
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}
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/* Initialise the guessed poly to the starting value. */
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gpoly = pclone(guess->spoly);
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/* Clear the least significant term, to be set in the
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* loop. qpoly does not need fixing as it is only
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* compared with odd polys.
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*/
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if(plen(gpoly))
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pshift(&gpoly, gpoly, 0UL, 0UL, plen(gpoly) - 1UL, 1UL);
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while(piter(&gpoly) && (~rflags & R_HAVEQ || pcmp(&gpoly, &qpoly) < 0)) {
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/* For each possible poly of this size, try
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* dividing all the differences in the list.
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*/
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if(!(spin++ & R_SPMASK)) {
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uprog(gpoly, guess->flags, seq++);
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}
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for(wptr = pworks; plen(*wptr); ++wptr) {
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/* straight divide message by poly, don't multiply by x^n */
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rem = pcrc(*wptr, gpoly, pzero, pzero, 0);
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if(ptst(rem)) {
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pfree(&rem);
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break;
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} else
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pfree(&rem);
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}
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/* If gpoly divides all the differences, it is a
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* candidate. Search for an Init value for this
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* poly or if Init is known, log the result.
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*/
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if(!plen(*wptr)) {
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/* gpoly is a candidate poly */
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if(rflags & R_HAVEI && rflags & R_HAVEX)
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chkres(&resc, &result, gpoly, guess->init, guess->flags, guess->xorout, args, argpolys);
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else if(rflags & R_HAVEI)
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calout(&resc, &result, gpoly, guess->init, guess->flags, args, argpolys);
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else if(rflags & R_HAVEX)
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calini(&resc, &result, gpoly, guess->flags, guess->xorout, args, argpolys);
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else
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engini(&resc, &result, gpoly, guess->flags, args, argpolys);
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}
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if(!piter(&gpoly))
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break;
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}
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/* Finished with gpoly and the differences list, free them.
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*/
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pfree(&gpoly);
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for(wptr = pworks; plen(*wptr); ++wptr)
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pfree(wptr);
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free(pworks);
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}
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else if(rflags & R_HAVEI && rflags & R_HAVEX)
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/* All parameters are known! Submit the result if we get here */
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chkres(&resc, &result, guess->spoly, guess->init, guess->flags, guess->xorout, args, argpolys);
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else if(rflags & R_HAVEI)
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/* Poly and Init are known, calculate XorOut */
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calout(&resc, &result, guess->spoly, guess->init, guess->flags, args, argpolys);
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else if(rflags & R_HAVEX)
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/* Poly and XorOut are known, calculate Init */
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calini(&resc, &result, guess->spoly, guess->flags, guess->xorout, args, argpolys);
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else
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/* Poly is known but not Init; search for Init. */
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engini(&resc, &result, guess->spoly, guess->flags, args, argpolys);
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requit:
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if(!(result = realloc(result, ++resc * sizeof(model_t)))) {
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uerror("cannot reallocate result array");
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return NULL;
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}
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rptr = result + resc - 1;
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rptr->spoly = pzero;
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rptr->init = pzero;
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rptr->flags = 0;
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rptr->xorout = pzero;
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rptr->check = pzero;
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rptr->magic = pzero;
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rptr->name = NULL;
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return(result);
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}
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static poly_t *
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modpol(const poly_t init, int rflags, int args, const poly_t *argpolys) {
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/* Produce, in ascending length order, a list of differences
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* between the arguments in the list by summing pairs of arguments.
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* If R_HAVEI is not set in rflags, only pairs of equal length are
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* summed.
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* Otherwise, sums of right-aligned pairs are also returned, with
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* the supplied init poly added to the leftmost terms of each
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* poly of the pair.
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*/
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poly_t work, swap, *result, *rptr, *iptr;
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const poly_t *aptr, *bptr, *eptr = argpolys + args;
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unsigned long alen, blen;
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if(args < 2) return(NULL);
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result = calloc(((((args - 1) * args) >> 1) + 1) * sizeof(poly_t), sizeof(char));
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if(!result)
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uerror("cannot allocate memory for codeword table");
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rptr = result;
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for(aptr = argpolys; aptr < eptr; ++aptr) {
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alen = plen(*aptr);
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for(bptr = aptr + 1; bptr < eptr; ++bptr) {
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blen = plen(*bptr);
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if(alen == blen) {
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work = pclone(*aptr);
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psum(&work, *bptr, 0UL);
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} else if(rflags & R_HAVEI && alen < blen) {
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work = pclone(*bptr);
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psum(&work, *aptr, blen - alen);
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psum(&work, init, 0UL);
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psum(&work, init, blen - alen);
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} else if(rflags & R_HAVEI /* && alen > blen */) {
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work = pclone(*aptr);
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psum(&work, *bptr, alen - blen);
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psum(&work, init, 0UL);
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psum(&work, init, alen - blen);
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} else
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work = pzero;
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if(plen(work))
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pnorm(&work);
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if((blen = plen(work))) {
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/* insert work into result[] in ascending order of length */
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for(iptr = result; iptr < rptr; ++iptr) {
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if(plen(work) < plen(*iptr)) {
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swap = *iptr;
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*iptr = work;
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work = swap;
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}
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else if(plen(*iptr) == blen && !pcmp(&work, iptr)) {
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pfree(&work);
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work = *--rptr;
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break;
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}
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}
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*rptr++ = work;
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}
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}
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}
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*rptr = pzero;
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return(result);
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}
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static void
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engini(int *resc, model_t **result, const poly_t divisor, int flags, int args, const poly_t *argpolys) {
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/* Search for init values implied by the arguments.
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* Method from: Ewing, Gregory C. (March 2010).
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* "Reverse-Engineering a CRC Algorithm". Christchurch:
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* University of Canterbury.
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* <http://www.cosc.canterbury.ac.nz/greg.ewing/essays/
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* CRC-Reverse-Engineering.html>
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*/
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poly_t apoly = PZERO, bpoly, pone = PZERO, *mat, *jptr;
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const poly_t *aptr, *bptr, *iptr;
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unsigned long alen, blen, dlen, ilen, i, j;
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int cy;
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dlen = plen(divisor);
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/* Allocate the CRC matrix */
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mat = (poly_t *) calloc((dlen << 1) * sizeof(poly_t), sizeof(char));
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if(!mat)
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uerror("cannot allocate memory for CRC matrix");
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/* Find arguments of the two shortest lengths */
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alen = blen = plen(*(aptr = bptr = iptr = argpolys));
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for(++iptr; iptr < argpolys + args; ++iptr) {
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ilen = plen(*iptr);
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if(ilen < alen) {
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bptr = aptr; blen = alen;
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aptr = iptr; alen = ilen;
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} else if(ilen > alen && (aptr == bptr || ilen < blen)) {
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bptr = iptr; blen = ilen;
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}
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}
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if(aptr == bptr) {
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/* if no arguments are suitable, calculate Init with an
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* assumed XorOut of 0. Create a padded XorOut
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*/
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palloc(&apoly, dlen);
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calini(resc, result, divisor, flags, apoly, args, argpolys);
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pfree(&apoly);
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free(mat);
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return;
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}
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/* Find the potential contribution of the bottom bit of Init */
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palloc(&pone, 1UL);
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piter(&pone);
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if(blen < (dlen << 1)) {
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palloc(&apoly, dlen); /* >= 1 */
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psum(&apoly, pone, (dlen << 1) - 1UL - blen); /* >= 0 */
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psum(&apoly, pone, (dlen << 1) - 1UL - alen); /* >= 1 */
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} else {
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palloc(&apoly, blen - dlen + 1UL); /* > dlen */
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psum(&apoly, pone, 0UL);
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psum(&apoly, pone, blen - alen); /* >= 1 */
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}
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if(plen(apoly) > dlen) {
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mat[dlen] = pcrc(apoly, divisor, pzero, pzero, 0);
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pfree(&apoly);
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} else {
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mat[dlen] = apoly;
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}
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/* Find the actual contribution of Init */
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apoly = pcrc(*aptr, divisor, pzero, pzero, 0);
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bpoly = pcrc(*bptr, divisor, pzero, apoly, 0);
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/* Populate the matrix */
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palloc(&apoly, 1UL);
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for(jptr=mat; jptr<mat+dlen; ++jptr)
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*jptr = pzero;
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for(iptr = jptr++; jptr < mat + (dlen << 1); iptr = jptr++)
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*jptr = pcrc(apoly, divisor, *iptr, pzero, P_MULXN);
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pfree(&apoly);
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/* Transpose the matrix, augment with the Init contribution
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* and convert to row echelon form
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*/
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for(i=0UL; i<dlen; ++i) {
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apoly = pzero;
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iptr = mat + (dlen << 1);
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for(j=0UL; j<dlen; ++j)
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ppaste(&apoly, *--iptr, i, j, j + 1UL, dlen + 1UL);
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if(ptst(apoly))
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ppaste(&apoly, bpoly, i, dlen, dlen + 1UL, dlen + 1UL);
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j = pfirst(apoly);
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while(j < dlen && !pident(mat[j], pzero)) {
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psum(&apoly, mat[j], 0UL); /* pfirst(apoly) > j */
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j = pfirst(apoly);
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}
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if(j < dlen)
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mat[j] = apoly; /* pident(mat[j], pzero) || pfirst(mat[j]) == j */
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else
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pfree(&apoly);
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}
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palloc(&bpoly, dlen + 1UL);
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psum(&bpoly, pone, dlen);
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/* Iterate through all solutions */
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do {
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/* Solve the matrix by Gaussian elimination.
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* The parity of the result, masked by each row, should be even.
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*/
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cy = 1;
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apoly = pclone(bpoly);
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jptr = mat + dlen;
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for(i=0UL; i<dlen; ++i) {
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/* Compute next bit of Init */
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if(pmpar(apoly, *--jptr))
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psum(&apoly, pone, dlen - 1UL - i);
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/* Toggle each zero row with carry, for next iteration */
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if(cy) {
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if(pident(*jptr, pzero)) {
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/* 0 to 1, no carry */
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*jptr = bpoly;
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cy = 0;
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} else if(pident(*jptr, bpoly)) {
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/* 1 to 0, carry forward */
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*jptr = pzero;
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}
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}
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}
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/* Trim the augment mask bit */
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praloc(&apoly, dlen);
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/* Test the Init value and add to results if correct */
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calout(resc, result, divisor, apoly, flags, args, argpolys);
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pfree(&apoly);
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} while(!cy);
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pfree(&pone);
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pfree(&bpoly);
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/* Free the matrix. */
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for(jptr=mat; jptr < mat + (dlen << 1); ++jptr)
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pfree(jptr);
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free(mat);
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}
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static void
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calout(int *resc, model_t **result, const poly_t divisor, const poly_t init, int flags, int args, const poly_t *argpolys) {
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/* Calculate Xorout, check it against all the arguments and
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* add to results if consistent.
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*/
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poly_t xorout;
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const poly_t *aptr, *iptr;
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unsigned long alen, ilen;
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if(args < 1) return;
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/* find argument of the shortest length */
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alen = plen(*(aptr = iptr = argpolys));
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for(++iptr; iptr < argpolys + args; ++iptr) {
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ilen = plen(*iptr);
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if(ilen < alen) {
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aptr = iptr; alen = ilen;
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}
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}
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xorout = pcrc(*aptr, divisor, init, pzero, 0);
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/* On little-endian algorithms, the calculations yield
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* the reverse of the actual xorout: in the Williams
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* model, the refout stage intervenes between init and
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* xorout.
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*/
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if(flags & P_REFOUT)
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prev(&xorout);
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/* Submit the model to the results table.
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* Could skip the shortest argument but we wish to check our
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* calculation.
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*/
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chkres(resc, result, divisor, init, flags, xorout, args, argpolys);
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pfree(&xorout);
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}
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static void
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calini(int *resc, model_t **result, const poly_t divisor, int flags, const poly_t xorout, int args, const poly_t *argpolys) {
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/* Calculate Init, check it against all the arguments and add to
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* results if consistent.
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*/
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poly_t rcpdiv, rxor, arg, init;
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const poly_t *aptr, *iptr;
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unsigned long alen, ilen;
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if(args < 1) return;
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/* find argument of the shortest length */
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alen = plen(*(aptr = iptr = argpolys));
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for(++iptr; iptr < argpolys + args; ++iptr) {
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ilen = plen(*iptr);
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if(ilen < alen) {
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aptr = iptr; alen = ilen;
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}
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}
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rcpdiv = pclone(divisor);
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prcp(&rcpdiv);
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/* If the algorithm is reflected, an ordinary CRC requires the
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* model's XorOut to be reversed, as XorOut follows the RefOut
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* stage. To reverse the CRC calculation we need rxor to be the
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* mirror image of the forward XorOut.
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*/
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rxor = pclone(xorout);
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if(~flags & P_REFOUT)
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prev(&rxor);
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arg = pclone(*aptr);
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prev(&arg);
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init = pcrc(arg, rcpdiv, rxor, pzero, 0);
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pfree(&arg);
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pfree(&rxor);
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pfree(&rcpdiv);
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prev(&init);
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/* Submit the model to the results table.
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* Could skip the shortest argument but we wish to check our
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* calculation.
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*/
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chkres(resc, result, divisor, init, flags, xorout, args, argpolys);
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pfree(&init);
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}
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static void
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chkres(int *resc, model_t **result, const poly_t divisor, const poly_t init, int flags, const poly_t xorout, int args, const poly_t *argpolys) {
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/* Checks a model against the argument list, and adds to the
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* external results table if consistent.
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* Extends the result array and updates the external pointer if
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* necessary.
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*/
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model_t *rptr;
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poly_t xor, crc;
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const poly_t *aptr = argpolys, *const eptr = argpolys + args;
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|
|
|
/* If the algorithm is reflected, an ordinary CRC requires the
|
|
* model's XorOut to be reversed, as XorOut follows the RefOut
|
|
* stage.
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|
*/
|
|
xor = pclone(xorout);
|
|
if(flags & P_REFOUT)
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|
prev(&xor);
|
|
|
|
for(; aptr < eptr; ++aptr) {
|
|
crc = pcrc(*aptr, divisor, init, xor, 0);
|
|
if(ptst(crc)) {
|
|
pfree(&crc);
|
|
break;
|
|
} else {
|
|
pfree(&crc);
|
|
}
|
|
}
|
|
pfree(&xor);
|
|
if(aptr != eptr) return;
|
|
|
|
*result = realloc(*result, ++*resc * sizeof(model_t));
|
|
if (!*result) {
|
|
uerror("cannot reallocate result array");
|
|
return;
|
|
}
|
|
|
|
rptr = *result + *resc - 1;
|
|
rptr->spoly = pclone(divisor);
|
|
rptr->init = pclone(init);
|
|
rptr->flags = flags;
|
|
rptr->xorout = pclone(xorout);
|
|
rptr->check = pzero;
|
|
rptr->magic = pzero;
|
|
rptr->name = NULL;
|
|
|
|
/* compute check value for this model */
|
|
mcheck(rptr);
|
|
|
|
/* callback to notify new model */
|
|
ufound(rptr);
|
|
}
|