crypto/bn/bn_asn1.c

/* Copyright (c) 2015, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

#include <openssl/bn.h>

#include <openssl/bytestring.h>
#include <openssl/err.h>


int BN_cbs2unsigned(CBS *cbs, BIGNUM *ret) {
  CBS child;
  if (!CBS_get_asn1(cbs, &child, CBS_ASN1_INTEGER) ||
      CBS_len(&child) == 0) {
    OPENSSL_PUT_ERROR(BN, BN_R_BAD_ENCODING);
    return 0;
  }

  if (CBS_data(&child)[0] & 0x80) {
    OPENSSL_PUT_ERROR(BN, BN_R_NEGATIVE_NUMBER);
    return 0;
  }

  /* INTEGERs must be minimal. */
  if (CBS_data(&child)[0] == 0x00 &&
      CBS_len(&child) > 1 &&
      !(CBS_data(&child)[1] & 0x80)) {
    OPENSSL_PUT_ERROR(BN, BN_R_BAD_ENCODING);
    return 0;
  }

  return BN_bin2bn(CBS_data(&child), CBS_len(&child), ret) != NULL;
}

int BN_cbs2unsigned_buggy(CBS *cbs, BIGNUM *ret) {
  CBS child;
  if (!CBS_get_asn1(cbs, &child, CBS_ASN1_INTEGER) ||
      CBS_len(&child) == 0) {
    OPENSSL_PUT_ERROR(BN, BN_R_BAD_ENCODING);
    return 0;
  }

  /* INTEGERs must be minimal. */
  if (CBS_data(&child)[0] == 0x00 &&
      CBS_len(&child) > 1 &&
      !(CBS_data(&child)[1] & 0x80)) {
    OPENSSL_PUT_ERROR(BN, BN_R_BAD_ENCODING);
    return 0;
  }

  /* This function intentionally does not reject negative numbers. Estonian IDs
   * issued between September 2014 to September 2015 are broken and use negative
   * moduli. They last five years and are common enough that we need to work
   * around this bug. See https://crbug.com/532048.
   *
   * TODO(davidben): Remove this code and callers in September 2019 when all the
   * bad certificates have expired. */
  return BN_bin2bn(CBS_data(&child), CBS_len(&child), ret) != NULL;
}

int BN_bn2cbb(CBB *cbb, const BIGNUM *bn) {
  /* Negative numbers are unsupported. */
  if (BN_is_negative(bn)) {
    OPENSSL_PUT_ERROR(BN, BN_R_NEGATIVE_NUMBER);
    return 0;
  }

  CBB child;
  if (!CBB_add_asn1(cbb, &child, CBS_ASN1_INTEGER)) {
    OPENSSL_PUT_ERROR(BN, BN_R_ENCODE_ERROR);
    return 0;
  }

  /* The number must be padded with a leading zero if the high bit would
   * otherwise be set (or |bn| is zero). */
  if (BN_num_bits(bn) % 8 == 0 &&
      !CBB_add_u8(&child, 0x00)) {
    OPENSSL_PUT_ERROR(BN, BN_R_ENCODE_ERROR);
    return 0;
  }

  uint8_t *out;
  if (!CBB_add_space(&child, &out, BN_num_bytes(bn))) {
    OPENSSL_PUT_ERROR(BN, BN_R_ENCODE_ERROR);
    return 0;
  }
  BN_bn2bin(bn, out);
  if (!CBB_flush(cbb)) {
    OPENSSL_PUT_ERROR(BN, BN_R_ENCODE_ERROR);
    return 0;
  }
  return 1;
}