path: root/asn1.c

/*
 * asn1.c
 * ------
 * Minimal ASN.1 implementation in support of Cryptech libhal.
 *
 * The functions in this module are not intended to be part of the
 * public API.  Rather, these are utility functions used by more than
 * one module within the library, which would otherwise have to be
 * duplicated.  The main reason for keeping these private is to avoid
 * having the public API depend on any details of the underlying
 * bignum implementation (currently libtfm, but that might change).
 *
 * As of this writing, the ASN.1 support we need is quite minimal, so,
 * rather than attempting to clean all the unecessary cruft out of a
 * general purpose ASN.1 implementation, we hand code the very small
 * number of data types we need.  At some point this will probably
 * become impractical, at which point we might want to look into using
 * something like the asn1c compiler.
 *
 * Authors: Rob Austein
 * Copyright (c) 2015, NORDUnet A/S
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 * - Neither the name of the NORDUnet nor the names of its contributors may
 *   be used to endorse or promote products derived from this software
 *   without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <stdint.h>
#include <assert.h>

#include "hal.h"

#include "asn1_internal.h"

/*
 * Encode tag and length fields of an ASN.1 object.
 *
 * Sets *der_len to the size of of the ASN.1 header (tag and length
 * fields); caller supplied length of value field, so presumably
 * already knows it.
 *
 * If der is NULL, just return the size of the header that would be
 * encoded and returns HAL_OK.
 *
 * If der isn't NULL, returns HAL_ERROR_RESULT_TOO_LONG unless full
 * header plus value will fit; this is a bit weird, but is useful when
 * using this to construct encoders for complte ASN.1 objects.
 */

hal_error_t hal_asn1_encode_header(const uint8_t tag,
				   const size_t value_len,
				   uint8_t *der, size_t *der_len, const size_t der_max)
{
  size_t header_len = 2;	/* Shortest encoding is one octet each for tag and length */

  if (value_len >= 128)		/* Add octets for longer length encoding as needed */
    for (size_t n = value_len; n > 0; n >>= 8)
      ++header_len;

  if (der_len != NULL)
    *der_len = header_len;

  if (der == NULL)		/* If caller just wanted the length, we're done */
    return HAL_OK;

  /*
   * Make sure there's enough room for header + value, then encode.
   */

  if (value_len + header_len > der_max)
    return HAL_ERROR_RESULT_TOO_LONG;

  *der++ = tag;

  if (value_len < 128) {
    *der = (uint8_t) value_len;
  }

  else {
    *der = 0x80 | (uint8_t) (header_len -= 2);
    for (size_t n = value_len; n > 0 && header_len > 0; n >>= 8)
      der[header_len--] = (uint8_t) (n & 0xFF);
  }

  return HAL_OK;
}

/*
 * Encode an unsigned ASN.1 INTEGER from a libtfm bignum.  If der is
 * NULL, just return the length of what we would have encoded.
 */

hal_error_t hal_asn1_encode_integer(const fp_int * const bn,
				    uint8_t *der, size_t *der_len, const size_t der_max)
{
  if (bn == NULL)
    return HAL_ERROR_BAD_ARGUMENTS;

  /*
   * We only handle unsigned INTEGERs, so we need to pad data with a
   * leading zero if the most significant bit is set, to avoid
   * flipping the ASN.1 sign bit.  Conveniently, this also handles the
   * difference between libtfm's and ASN.1's encoding of zero.
   */

  if (fp_cmp_d(unconst_fp_int(bn), 0) == FP_LT)
    return HAL_ERROR_BAD_ARGUMENTS;

  const int leading_zero = fp_iszero(bn) || (fp_count_bits(unconst_fp_int(bn)) & 7) == 0;
  const size_t vlen = fp_unsigned_bin_size(unconst_fp_int(bn)) + leading_zero;
  hal_error_t err;
  size_t hlen;

  err = hal_asn1_encode_header(ASN1_INTEGER, vlen, der, &hlen, der_max);

  if (der_len != NULL)
    *der_len = hlen + vlen;

  if (der == NULL || err != HAL_OK)
    return err;

  assert(hlen + vlen <= der_max);

  der += hlen;
  if (leading_zero)
    *der++ = 0x00;
  fp_to_unsigned_bin(unconst_fp_int(bn), der);

  return HAL_OK;
}

/*
 * Encode a public key into an RFC 5280 SubjectPublicKeyInfo.
 */

hal_error_t hal_asn1_encode_spki(const uint8_t * const alg_oid,   const size_t alg_oid_len,
                                 const uint8_t * const curve_oid, const size_t curve_oid_len,
                                 const uint8_t * const pubkey,    const size_t pubkey_len,
                                 uint8_t *der, size_t *der_len, const size_t der_max)
{
  if (alg_oid == NULL || alg_oid_len == 0 || pubkey == NULL || pubkey_len == 0 || (curve_oid == NULL && curve_oid_len != 0))
    return HAL_ERROR_BAD_ARGUMENTS;

  const uint8_t curve_oid_tag = curve_oid == NULL ? ASN1_NULL : ASN1_OBJECT_IDENTIFIER;

  hal_error_t err;

  size_t hlen, hlen_spki, hlen_algid, hlen_alg, hlen_curve, hlen_bit;

  if ((err = hal_asn1_encode_header(ASN1_OBJECT_IDENTIFIER, alg_oid_len,    NULL, &hlen_alg,   0)) != HAL_OK ||
      (err = hal_asn1_encode_header(curve_oid_tag,          curve_oid_len,  NULL, &hlen_curve, 0)) != HAL_OK ||
      (err = hal_asn1_encode_header(ASN1_BIT_STRING,        1 + pubkey_len, NULL, &hlen_bit,   0)) != HAL_OK)
    return err;

  const size_t algid_len = hlen_alg + alg_oid_len + hlen_curve + curve_oid_len;

  if ((err = hal_asn1_encode_header(ASN1_SEQUENCE,          algid_len,     NULL, &hlen_algid, 0)) != HAL_OK)
    return err;

  const size_t vlen = hlen_algid + hlen_alg + alg_oid_len + hlen_curve + curve_oid_len + hlen_bit + 1 + pubkey_len;

  if ((err = hal_asn1_encode_header(ASN1_SEQUENCE,          vlen,          NULL, &hlen_spki,  0)) != HAL_OK)
    return err;

  /*
   * Handle pubkey early, in case it was staged into our output buffer.
   */
  if (der != NULL && hlen_spki + vlen <= der_max)
    memmove(der + hlen_spki + vlen - pubkey_len, pubkey, pubkey_len);

  err = hal_asn1_encode_header(ASN1_SEQUENCE, vlen, der, &hlen, der_max);

  if (der_len != NULL)
    *der_len = hlen + vlen;

  if (der == NULL || err != HAL_OK)
    return err;

  uint8_t *d = der + hlen;
  memset(d, 0, vlen - pubkey_len);

  if ((err = hal_asn1_encode_header(ASN1_SEQUENCE, algid_len, d, &hlen, der + der_max - d)) != HAL_OK)
    return err;
  d += hlen;

  if ((err = hal_asn1_encode_header(ASN1_OBJECT_IDENTIFIER, alg_oid_len, d, &hlen, der + der_max - d)) != HAL_OK)
    return err;
  d += hlen;
  memcpy(d, alg_oid, alg_oid_len);
  d += alg_oid_len;

  if ((err = hal_asn1_encode_header(curve_oid_tag, curve_oid_len, d, &hlen, der + der_max - d)) != HAL_OK)
    return err;
  d += hlen;
  if (curve_oid != NULL)
    memcpy(d, curve_oid, curve_oid_len);
  d += curve_oid_len;

  if ((err = hal_asn1_encode_header(ASN1_BIT_STRING, 1 + pubkey_len, d, &hlen, der + der_max - d)) != HAL_OK)
    return err;
  d += hlen;
  *d++ = 0x00;

  d += pubkey_len;              /* pubkey handled early, above. */

  assert(d == der + hlen_spki + vlen);
  assert(d <= der + der_max);

  return HAL_OK;
}

/*
 * Parse tag and length of an ASN.1 object.  Tag must match value
 * specified by the caller.  On success, sets hlen and vlen to lengths
 * of header and value, respectively.
 */

hal_error_t hal_asn1_decode_header(const uint8_t tag,
				   const uint8_t * const der, size_t der_max,
				   size_t *hlen, size_t *vlen)
{
  assert(der != NULL && hlen != NULL && vlen != NULL);

  if (der_max < 2 || der[0] != tag)
    return HAL_ERROR_ASN1_PARSE_FAILED;

  if ((der[1] & 0x80) == 0) {
    *hlen = 2;
    *vlen = der[1];
  }

  else {
    *hlen = 2 + (der[1] & 0x7F);
    *vlen = 0;

    if (*hlen > der_max)
      return HAL_ERROR_ASN1_PARSE_FAILED;

    for (size_t i = 2; i < *hlen; i++)
      *vlen = (*vlen << 8) + der[i];
  }

  if (*hlen + *vlen > der_max)
    return HAL_ERROR_ASN1_PARSE_FAILED;

  return HAL_OK;
}

/*
 * Decode an ASN.1 INTEGER into a libtfm bignum.  Since we only
 * support (or need to support, or expect to see) unsigned integers,
 * we return failure if the sign bit is set in the ASN.1 INTEGER.
 */

hal_error_t hal_asn1_decode_integer(fp_int *bn,
				    const uint8_t * const der, size_t *der_len, const size_t der_max)
{
  if (bn == NULL || der == NULL)
    return HAL_ERROR_BAD_ARGUMENTS;

  hal_error_t err;
  size_t hlen, vlen;

  if ((err = hal_asn1_decode_header(ASN1_INTEGER, der, der_max, &hlen, &vlen)) != HAL_OK)
    return err;

  if (der_len != NULL)
    *der_len = hlen + vlen;

  if (vlen < 1 || (der[hlen] & 0x80) != 0x00)
    return HAL_ERROR_ASN1_PARSE_FAILED;

  fp_init(bn);
  fp_read_unsigned_bin(bn, (uint8_t *) der + hlen, vlen);
  return HAL_OK;
}

/*
 * Decode a public key from an RFC 5280 SubjectPublicKeyInfo.
 */

hal_error_t hal_asn1_decode_spki(const uint8_t **alg_oid,   size_t *alg_oid_len,
                                 const uint8_t **curve_oid, size_t *curve_oid_len,
                                 const uint8_t **pubkey,    size_t *pubkey_len,
                                 const uint8_t *const der,  const size_t der_len)
{
  if (alg_oid == NULL || alg_oid_len == NULL || curve_oid == NULL || curve_oid_len == NULL ||
      pubkey == NULL || pubkey_len == NULL || der == NULL)
    return HAL_ERROR_BAD_ARGUMENTS;

  const uint8_t * const der_end = der + der_len;
  const uint8_t *d = der;

  size_t hlen, vlen;
  hal_error_t err;

  if ((err = hal_asn1_decode_header(ASN1_SEQUENCE, d, der_end - d, &hlen, &vlen)) != HAL_OK)
    return err;
  d += hlen;

  if ((err = hal_asn1_decode_header(ASN1_SEQUENCE, d, der_end - d, &hlen, &vlen)) != HAL_OK)
    return err;
  d += hlen;

  const uint8_t * const algid_end = d + vlen;

  if ((err = hal_asn1_decode_header(ASN1_OBJECT_IDENTIFIER, d, algid_end - d, &hlen, &vlen)) != HAL_OK)
    return err;
  d += hlen;
  if (vlen > algid_end - d)
    return HAL_ERROR_ASN1_PARSE_FAILED;
  *alg_oid = d;
  *alg_oid_len = vlen;
  d += vlen;

  *curve_oid = NULL;
  *curve_oid_len = 0;
    
  if (d < algid_end) {
    switch (*d) {

    case ASN1_OBJECT_IDENTIFIER:
      if ((err = hal_asn1_decode_header(ASN1_OBJECT_IDENTIFIER, d, algid_end - d, &hlen, &vlen)) != HAL_OK)
        return err;
      d += hlen;
      if (vlen > algid_end - d)
        return HAL_ERROR_ASN1_PARSE_FAILED;
      *curve_oid = d;
      *curve_oid_len = vlen;
      d += vlen;
      break;

    case ASN1_NULL:
      if ((err = hal_asn1_decode_header(ASN1_NULL, d, algid_end - d, &hlen, &vlen)) != HAL_OK)
        return err;
      d += hlen;
      if (vlen == 0)
        break;

    default:
      return HAL_ERROR_ASN1_PARSE_FAILED;
    }
  }

  if (d != algid_end)
    return HAL_ERROR_ASN1_PARSE_FAILED;

  if ((err = hal_asn1_decode_header(ASN1_BIT_STRING, d, der_end - d, &hlen, &vlen)) != HAL_OK)
    return err;
  d += hlen;
  if (vlen >= algid_end - d || vlen == 0 || *d != 0x00)
    return HAL_ERROR_ASN1_PARSE_FAILED;
  *pubkey = ++d;
  *pubkey_len = --vlen;
  d += vlen;

  if (d != der_end)
    return HAL_ERROR_ASN1_PARSE_FAILED;

  return HAL_OK;
}

/*
 * Local variables:
 * indent-tabs-mode: nil
 * End:
 */