proxmark3/client/deps/reveng/model.c

/* model.c
 * Greg Cook, 23/Feb/2019
 */

/* CRC RevEng: arbitrary-precision CRC calculator and algorithm finder
 * Copyright (C) 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018,
 * 2019  Gregory Cook
 *
 * This file is part of CRC RevEng.
 *
 * CRC RevEng 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.
 *
 * CRC RevEng 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 CRC RevEng.  If not, see <https://www.gnu.org/licenses/>.
 */

/* 2018-12-17: mnovel() clears class flags
 * 2017-02-19: revised residue calculation for crossed-endian models
 * 2017-02-05: added magic field
 * 2016-02-22: split off preset.c
 * 2012-03-03: single-line Williams model string conversion
 * 2011-09-03: added mrev(), mnovel()
 * 2011-01-17: fixed ANSI C warnings (except preset models)
 * 2010-12-26: renamed CRC RevEng
 * 2010-12-18: minor change to mtostr() output format
 * 2010-12-15: added mcmp()
 * 2010-12-14: finished mtostr()
 * 2010-12-12: started models.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <inttypes.h>
#include "reveng.h"

/* Private declarations */

static const poly_t pzero = PZERO;

/* Definitions */

void mcpy(model_t *dest, const model_t *src) {
    /* Copies the parameters of src to dest.
     * dest must be an initialised model.
     */
    if (!dest || !src) return;
    pcpy(&dest->spoly, src->spoly);
    pcpy(&dest->init, src->init);
    pcpy(&dest->xorout, src->xorout);
    pcpy(&dest->check, src->check);
    pcpy(&dest->magic, src->magic);
    dest->flags = src->flags;
    /* link to the name as it is static */
    dest->name = src->name;
}

void mfree(model_t *model) {
    /* Frees the parameters of model. */
    if (!model) return;
    pfree(&model->spoly);
    pfree(&model->init);
    pfree(&model->xorout);
    pfree(&model->check);
    pfree(&model->magic);
    /* not name as it is static */
    /* not model either, it might point to an array! */
}

int mcmp(const model_t *a, const model_t *b) {
    /* Compares a and b for identical effect, i.e. disregarding
     * trailing zeroes in parameter polys.
     * Intended for bsearch().
     */
    int result;
    if (!a || !b) return (!b - !a);
    if ((result = psncmp(&a->spoly, &b->spoly))) return (result);
    if ((result = psncmp(&a->init, &b->init))) return (result);
    if ((a->flags & P_REFIN) && (~b->flags & P_REFIN)) return (1);
    if ((~a->flags & P_REFIN) && (b->flags & P_REFIN)) return (-1);
    if ((a->flags & P_REFOUT) && (~b->flags & P_REFOUT)) return (1);
    if ((~a->flags & P_REFOUT) && (b->flags & P_REFOUT)) return (-1);
    return (psncmp(&a->xorout, &b->xorout));
}

char *mtostr(const model_t *model) {
    /* Returns a malloc()-ed string containing a Williams model
     * record representing the input model.
     * mcanon() should be called on the argument before printing.
     */
    size_t size;
    char *polystr, *initstr, *xorotstr, *checkstr, *magicstr,
         strbuf[512], *string = NULL;

    if (!model) return (NULL);
    polystr = ptostr(model->spoly, P_RTJUST, 4);
    initstr = ptostr(model->init, P_RTJUST, 4);
    xorotstr = ptostr(model->xorout, P_RTJUST, 4);
    checkstr = ptostr(model->check, P_RTJUST, 4);
    magicstr = ptostr(model->magic, P_RTJUST, 4);

    sprintf(strbuf, "%lu", plen(model->spoly));
    size =
        82
        + strlen(strbuf)
        + (polystr && *polystr ? strlen(polystr) : 6)
        + (initstr && *initstr ? strlen(initstr) : 6)
        + ((model->flags & P_REFIN) ? 4 : 5)
        + ((model->flags & P_REFOUT) ? 4 : 5)
        + (xorotstr && *xorotstr ? strlen(xorotstr) : 6)
        + (checkstr && *checkstr ? strlen(checkstr) : 6)
        + (magicstr && *magicstr ? strlen(magicstr) : 6)
        + (model->name && *model->name ? 2 + strlen(model->name) : 6);
    if ((string = calloc(size, sizeof(uint8_t)))) {
        sprintf(strbuf, "\"%s\"", model->name);
        sprintf(string,
                "width=%lu  "
                "poly=0x%s  "
                "init=0x%s  "
                "refin=%s  "
                "refout=%s  "
                "xorout=0x%s  "
                "check=0x%s  "
                "residue=0x%s  "
                "name=%s",
                plen(model->spoly),
                polystr && *polystr ? polystr : "(none)",
                initstr && *initstr ? initstr :  "(none)",
                (model->flags & P_REFIN) ? "true" : "false",
                (model->flags & P_REFOUT) ? "true" : "false",
                xorotstr && *xorotstr ? xorotstr : "(none)",
                checkstr && *checkstr ? checkstr : "(none)",
                magicstr && *magicstr ? magicstr : "(none)",
                (model->name && *model->name) ? strbuf : "(none)");
    }
    free(polystr);
    free(initstr);
    free(xorotstr);
    free(checkstr);
    free(magicstr);
    if (!string)
        uerror("cannot allocate memory for model description");
    return (string);
}

void mcanon(model_t *model) {
    /* canonicalise a model */
    unsigned long dlen;

    if (!model) return;

    /* extending on the right here. This preserves the functionality
     * of a presumed working model.
     */
    psnorm(&model->spoly);
    dlen = plen(model->spoly);
    praloc(&model->init, dlen);
    praloc(&model->xorout, dlen);

    /* only calculate Check if missing.  Relying on all functions
     * changing parameters to call mnovel().  This is to ensure that
     * the Check value stored in the preset table is printed when
     * the model is dumped.  If something goes wrong with the
     * calculator then the discrepancy with the stored Check value
     * might be noticed.  Storing the Check value with each preset
     * is highly preferred.
     */
    if (!(plen(model->check) && plen(model->magic)))
        mcheck(model);
}

void mcheck(model_t *model) {
    /* calculate a check for the model */
    poly_t checkstr, check, xorout, magic;

    /* erase existing check and magic.  Models with these
     * fields recalculated should have no name.
     */
    mnovel(model);

    /* generate the check string with the correct bit order */
    checkstr = strtop("313233343536373839", model->flags, 8);
    check = pcrc(checkstr, model->spoly, model->init, pzero, model->flags);
    pfree(&checkstr);
    if (model->flags & P_REFOUT)
        prev(&check);
    psum(&check, model->xorout, 0UL);
    model->check = check;

    /* calculate residue by emulating receipt of error-free message
     * The residue of a crossed-endian model is calculated assuming
     * that the characters of the received CRC are specially
     * reflected before submitting the codeword.
     */
    xorout = pclone(model->xorout);
    if (model->flags & P_REFOUT)
        prev(&xorout);
    magic = pcrc(xorout, model->spoly, pzero, pzero, model->flags);
    pfree(&xorout);
    if (model->flags & P_REFIN)
        prev(&magic);
    model->magic = magic;
}

void mrev(model_t *model) {
    /* reverse the model to calculate reversed CRCs */
    /* Here we invert RefIn and RefOut so that the user need only
     * reverse the order of characters in the arguments, not the
     * characters themselves.  If RefOut=True, the mirror image of
     * Init seen through RefOut becomes XorOut, and as RefOut
     * becomes false, the XorOut value moved to Init stays upright.
     * If RefOut=False, Init transfers to XorOut without reflection
     * but the new Init must be reflected to present the same image,
     * as RefOut becomes true.
     */
    poly_t temp;

    prcp(&model->spoly);
    if (model->flags & P_REFOUT)
        prev(&model->init);
    else
        prev(&model->xorout);

    /* exchange init and xorout */
    temp = model->init;
    model->init = model->xorout;
    model->xorout = temp;

    /* invert refin and refout */
    model->flags ^= P_REFIN | P_REFOUT;

    mnovel(model);
}

void mnovel(model_t *model) {
    /* remove name and check string from modified model */
    /* previous classification no longer applies */
    model->name = NULL;
    model->flags &= ~P_CLMASK;
    pfree(&model->check);
    pfree(&model->magic);
}