src/bignum.c - master - niceSOFT/libssh

src/bignum.c
107 строк3 KB
Jakub Jelen
bignum: Make sure the padding is large enough for the number
21 янв 2025, 13:32
21 янв 2025, 13:320cda1c0
/*
 * This file is part of the SSH Library
 *
 * Copyright (c) 2014 by Aris Adamantiadis <aris@badcode.be>
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library 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 Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <stdio.h>

#include "libssh/priv.h"
#include "libssh/bignum.h"
#include "libssh/string.h"

static ssh_string make_bignum_string(bignum num, size_t pad_to_len)
{
    ssh_string ptr = NULL;
    size_t pad = 0;
    size_t len = bignum_num_bytes(num);
    size_t bits = bignum_num_bits(num);

    if (pad_to_len == 0) {
        /* If the first bit is set we have a negative number */
        if (!(bits % 8) && bignum_is_bit_set(num, bits - 1)) {
            pad++;
        }
    } else {
        if (len > pad_to_len) {
            return NULL;
        }
        pad = pad_to_len - len;
    }

#ifdef DEBUG_CRYPTO
    SSH_LOG(SSH_LOG_TRACE, "%zu bits, %zu bytes, %zu padding", bits, len, pad);
#endif /* DEBUG_CRYPTO */

    ptr = ssh_string_new(len + pad);
    if (ptr == NULL) {
        return NULL;
    }

    /* We have a negative number so we need a leading zero */
    if (pad) {
        memset(ptr->data, 0, pad);
    }

    bignum_bn2bin(num, len, ptr->data + pad);

    return ptr;
}

ssh_string ssh_make_bignum_string(bignum num)
{
    return make_bignum_string(num, 0);
}

ssh_string ssh_make_padded_bignum_string(bignum num, size_t pad_len)
{
    return make_bignum_string(num, pad_len);
}

bignum ssh_make_string_bn(ssh_string string)
{
    bignum bn = NULL;
    size_t len = ssh_string_len(string);

#ifdef DEBUG_CRYPTO
    SSH_LOG(SSH_LOG_TRACE,
            "Importing a %zu bits, %zu bytes object ...",
            len * 8,
            len);
#endif /* DEBUG_CRYPTO */

    bignum_bin2bn(string->data, (int)len, &bn);

    return bn;
}

/* prints the bignum on stderr */
void ssh_print_bignum(const char *name, const_bignum num)
{
    unsigned char *hex = NULL;
    if (num != NULL) {
        bignum_bn2hex(num, &hex);
    }
    SSH_LOG(SSH_LOG_DEBUG,
            "%s value: %s",
            name,
            (hex == NULL) ? "(null)" : (char *)hex);
    ssh_crypto_free(hex);
}