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/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
/* include/k5-der.h - Distinguished Encoding Rules (DER) declarations */
/*
* Copyright (C) 2023 by the Massachusetts Institute of Technology.
* 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.
*
* 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.
*/
/*
* Most ASN.1 encoding and decoding is done using the table-driven framework in
* libkrb5. When that is not an option, these helpers can be used to encode
* and decode simple types.
*/
#ifndef K5_DER_H
#define K5_DER_H
#include <stdint.h>
#include <stdbool.h>
#include "k5-buf.h"
#include "k5-input.h"
/* Return the number of bytes needed to encode len as a DER encoding length. */
static inline size_t
k5_der_len_len(size_t len)
{
size_t llen;
if (len < 128)
return 1;
llen = 1;
while (len > 0) {
len >>= 8;
llen++;
}
return llen;
}
/* Return the number of bytes needed to encode a DER value (with identifier
* byte and length) for a given contents length. */
static inline size_t
k5_der_value_len(size_t contents_len)
{
return 1 + k5_der_len_len(contents_len) + contents_len;
}
/* Add a DER identifier byte (composed by the caller, including the ASN.1
* class, tag, and constructed bit) and length. */
static inline void
k5_der_add_taglen(struct k5buf *buf, uint8_t idbyte, size_t len)
{
uint8_t *p;
size_t llen = k5_der_len_len(len);
p = k5_buf_get_space(buf, 1 + llen);
if (p == NULL)
return;
*p++ = idbyte;
if (len < 128) {
*p = len;
} else {
*p = 0x80 | (llen - 1);
/* Encode the length bytes backwards so the most significant byte is
* first. */
p += llen;
while (len > 0) {
*--p = len & 0xFF;
len >>= 8;
}
}
}
/* Add a DER value (identifier byte, length, and contents). */
static inline void
k5_der_add_value(struct k5buf *buf, uint8_t idbyte, const void *contents,
size_t len)
{
k5_der_add_taglen(buf, idbyte, len);
k5_buf_add_len(buf, contents, len);
}
/*
* If the next byte in in matches idbyte and the subsequent DER length is
* valid, advance in past the value, set *contents_out to the value contents,
* and return true. Otherwise return false. Only set an error on in if the
* next bytes matches idbyte but the ensuing length is invalid. contents_out
* may be aliased to in; it will only be written to on successful decoding of a
* value.
*/
static inline bool
k5_der_get_value(struct k5input *in, uint8_t idbyte,
struct k5input *contents_out)
{
uint8_t lenbyte, i;
size_t len;
const void *bytes;
/* Do nothing if in is empty or the next byte doesn't match idbyte. */
if (in->status || in->len == 0 || *in->ptr != idbyte)
return false;
/* Advance past the identifier byte and decode the length. */
(void)k5_input_get_byte(in);
lenbyte = k5_input_get_byte(in);
if (lenbyte < 128) {
len = lenbyte;
} else {
len = 0;
for (i = 0; i < (lenbyte & 0x7F); i++) {
if (len > (SIZE_MAX >> 8)) {
k5_input_set_status(in, EOVERFLOW);
return false;
}
len = (len << 8) | k5_input_get_byte(in);
}
}
bytes = k5_input_get_bytes(in, len);
if (bytes == NULL)
return false;
k5_input_init(contents_out, bytes, len);
return true;
}
#endif /* K5_DER_H */
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