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This library is meant to be small and quick. It's based on WPACKET,
which was extended to support DER writing. The way it's used is a
bit unusual, as it's used to write the structures backward into a
given buffer. A typical quick call looks like this:
/*
* Fill in this structure:
*
* something ::= SEQUENCE {
* id OBJECT IDENTIFIER,
* x [0] INTEGER OPTIONAL,
* y [1] BOOLEAN OPTIONAL,
* n INTEGER
* }
*/
unsigned char buf[nnnn], *p = NULL;
size_t encoded_len = 0;
WPACKET pkt;
int ok;
ok = WPACKET_init_der(&pkt, buf, sizeof(buf)
&& DER_w_start_sequence(&pkt, -1)
&& DER_w_bn(&pkt, -1, bn)
&& DER_w_boolean(&pkt, 1, bool)
&& DER_w_precompiled(&pkt, -1, OID, sizeof(OID))
&& DER_w_end_sequence(&pkt, -1)
&& WPACKET_finish(&pkt)
&& WPACKET_get_total_written(&pkt, &encoded_len)
&& (p = WPACKET_get_curr(&pkt)) != NULL;
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11450)
49 lines
1.4 KiB
Plaintext
49 lines
1.4 KiB
Plaintext
=pod
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=head1 NAME
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DER_w_begin_sequence, DER_w_end_sequence
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- internal DER writers for DER constructed elements
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=head1 SYNOPSIS
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#include "internal/der.h"
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int DER_w_begin_sequence(WPACKET *pkt, int tag);
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int DER_w_end_sequence(WPACKET *pkt, int tag);
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=head1 DESCRIPTION
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All functions described here are wrappers for constructed structures,
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i.e. the ASN.1 SEQUENCE, SET and CHOICE specifications. They all come
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in pairs, as noted by the function names containing the words C<begin>
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and B<end>.
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When using these, special care must be taken to ensure that the ASN.1 tag
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value I<tag> is the same in the matching C<begin> and C<end> function calls.
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DER_w_begin_sequence() and DER_w_end_sequence() begins and ends a
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SEQUENCE.
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=head1 RETURN VALUES
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All the functions return 1 on success and 0 on failure. Failure may
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mean that the buffer held by the I<pkt> is too small, but may also
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mean that the values given to the functions are invalid, such as the provided
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I<tag> value being too large for the implementation.
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=head1 SEE ALSO
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L<DERlib(7)>
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=head1 COPYRIGHT
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Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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