/* $OpenBSD: asn1_lib.c,v 1.54 2022/05/05 19:18:56 jsing Exp $ */

/*

 * Copyright (c) 2021 Joel Sing <jsing@openbsd.org>

 *

 * Permission to use, copy, modify, and 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 <limits.h>

#include <stdlib.h>

#include "bytestring.h"

int

asn1_get_identifier_cbs(CBS *cbs, int der_mode, uint8_t *out_class,

    int *out_constructed, uint32_t *out_tag_number)

{

  uint8_t tag_class, tag_val;

  int tag_constructed;

  uint32_t tag_number;

  /*

   * Decode ASN.1 identifier octets - see ITU-T X.690 section 8.1.2.

   */

  *out_class = 0;

  *out_constructed = 0;

  *out_tag_number = 0;

  if (!CBS_get_u8(cbs, &tag_val))

    return 0;

  /*

   * ASN.1 tag class, encoding (primitive or constructed) and tag number

   * are encoded in one or more identifier octets - the first octet

   * contains the 2 bit tag class, the 1 bit encoding type and 5 bits

   * of tag number.

   *

   * For tag numbers larger than 30 (0x1e) the 5 bit tag number in the

   * first octet is set to all ones (0x1f) - the tag number is then

   * encoded in subsequent octets - each of which have a one bit

   * continuation flag and 7 bits of tag number in big-endian form.

   * The encoding should not contain leading zeros but can for BER.

   */

  tag_class = (tag_val >> 6) & 0x3;

  tag_constructed = (tag_val >> 5) & 0x1;

  tag_number = tag_val & 0x1f;

  /* Long form. */

  if (tag_number == 0x1f) {

    tag_number = 0;

    do {

      if (!CBS_get_u8(cbs, &tag_val))

        return 0;

      if (der_mode && tag_number == 0 && tag_val == 0x80)

        return 0;

      if (tag_number > (UINT32_MAX >> 7))

        return 0;

      tag_number = tag_number << 7 | (tag_val & 0x7f);

    } while ((tag_val & 0x80) != 0);

  }

  *out_class = tag_class;

  *out_constructed = tag_constructed;

  *out_tag_number = tag_number;

  return 1;

}

int

asn1_get_length_cbs(CBS *cbs, int der_mode, int *out_indefinite,

    size_t *out_length)

{

  uint8_t len_bytes;

  size_t length;

  uint8_t val;

  /*

   * Decode ASN.1 length octets - see ITU-T X.690 section 8.1.3.

   */

  *out_length = 0;

  *out_indefinite = 0;

  if (!CBS_get_u8(cbs, &val))

    return 0;

  /*

   * Short form - length is encoded in the lower 7 bits of a single byte.

   */

  if (val < 0x80) {

    *out_length = val;

    return 1;

  }

  /*

   * Indefinite length - content continues until an End of Content (EOC)

   * marker is reached. Must be used with constructed encoding.

   */

  if (val == 0x80) {

    *out_indefinite = 1;

    return 1;

  }

  /*

   * Long form - the lower 7 bits of the first byte specifies the number

   * of bytes used to encode the length, the following bytes specify the

   * length in big-endian form. The encoding should not contain leading

   * zeros but can for BER. A length value of 0x7f is invalid.

   */

  if ((len_bytes = val & 0x7f) == 0x7f)

    return 0;

  length = 0;

  while (len_bytes-- > 0) {

    if (!CBS_get_u8(cbs, &val))

      return 0;

    if (der_mode && length == 0 && val == 0)

      return 0;

    if (length > (SIZE_MAX >> 8))

      return 0;

    length = (length << 8) | val;

  }

  *out_length = length;

  return 1;

}

int

asn1_get_object_cbs(CBS *cbs, int der_mode, uint8_t *out_tag_class,

    int *out_constructed, uint32_t *out_tag_number, int *out_indefinite,

    size_t *out_length)

{

  int constructed, indefinite;

  uint32_t tag_number;

  uint8_t tag_class;

  size_t length;

  *out_tag_class = 0;

  *out_constructed = 0;

  *out_tag_number = 0;

  *out_indefinite = 0;

  *out_length = 0;

  if (!asn1_get_identifier_cbs(cbs, der_mode, &tag_class, &constructed,

      &tag_number))

    return 0;

  if (!asn1_get_length_cbs(cbs, der_mode, &indefinite, &length))

    return 0;

  /* Indefinite length can only be used with constructed encoding. */

  if (indefinite && !constructed)

    return 0;

  *out_tag_class = tag_class;

  *out_constructed = constructed;

  *out_tag_number = tag_number;

  *out_indefinite = indefinite;

  *out_length = length;

  return 1;

}

int

asn1_get_primitive(CBS *cbs, int der_mode, uint32_t *out_tag_number,

    CBS *out_content)

{

  int constructed, indefinite;

  uint32_t tag_number;

  uint8_t tag_class;

  size_t length;

  *out_tag_number = 0;

  CBS_init(out_content, NULL, 0);

  if (!asn1_get_identifier_cbs(cbs, der_mode, &tag_class, &constructed,

      &tag_number))

    return 0;

  if (!asn1_get_length_cbs(cbs, der_mode, &indefinite, &length))

    return 0;

  /* A primitive is not constructed and has a definite length. */

  if (constructed || indefinite)

    return 0;

  if (!CBS_get_bytes(cbs, out_content, length))

    return 0;

  *out_tag_number = tag_number;

  return 1;

}