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/* $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;
}
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