mirror of
https://github.com/openssl/openssl.git
synced 2024-11-27 05:21:51 +08:00
a55b00bdbc
Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/13038)
150 lines
4.9 KiB
Plaintext
150 lines
4.9 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
DERlib - internal OpenSSL DER library
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
OpenSSL contains an internal small DER reading and writing library,
|
|
as an alternative to the publicly known i2d and d2i functions. It's
|
|
solely constituted of functions that work as building blocks to create
|
|
more similar functions to encode and decode larger structures.
|
|
|
|
All these functions have similar function signatures (C<something>
|
|
will vary depending on what the function will encode):
|
|
|
|
int DER_w_something(WPACKET *pkt, int tag, ...);
|
|
|
|
=begin comment
|
|
|
|
When readers are added, add this:
|
|
|
|
int DER_r_something(PACKET *pkt, int tag, ...);
|
|
|
|
=end comment
|
|
|
|
I<pkt> is the packet context used, and I<tag> should be the
|
|
context-specific tag value of the element being handled, or -1 if there
|
|
is no tag number for that element (you may use the convenience macro
|
|
B<DER_NO_CONTEXT> instead of -1). Any argument following is the C
|
|
variable that's being encoded or decoded.
|
|
|
|
=head2 DER writers / encoders
|
|
|
|
DER writers are based in L<WPACKET(3)>, a generic packet writing
|
|
library, so before using any of them, I<pkt> must be initialized
|
|
using L<WPACKET_init_der(3)> or L<WPACKET_init_null_der(3)>
|
|
|
|
DER writers must be used in reverse order, except for the wrapping
|
|
functions that implement a constructed element. The latter are easily
|
|
recognised by their function name including the words C<begin> and
|
|
C<end>. As an example, we can look at the DSA signature structure,
|
|
which is defined like this in ASN.1 terms:
|
|
|
|
-- Copied from RFC 3279, section 2.2.2
|
|
Dss-Sig-Value ::= SEQUENCE {
|
|
r INTEGER,
|
|
s INTEGER }
|
|
|
|
With the DER library, this is the corresponding code, given two OpenSSL
|
|
B<BIGNUM>s I<r> and I<s>:
|
|
|
|
int ok = ossl_DER_w_begin_sequence(pkt, -1)
|
|
&& ossl_DER_w_bn(pkg, -1, s)
|
|
&& ossl_DER_w_bn(pkg, -1, r)
|
|
&& ossl_DER_w_end_sequence(pkt, -1);
|
|
|
|
As an example of the use of I<tag>, an ASN.1 element like this:
|
|
|
|
v [1] INTEGER OPTIONAL
|
|
|
|
Would be encoded like this:
|
|
|
|
ossl_DER_w_bn(pkt, 1, v)
|
|
|
|
=begin comment
|
|
|
|
=head2 DER readers / decoders
|
|
|
|
TBA
|
|
|
|
=end comment
|
|
|
|
=head1 EXAMPLES
|
|
|
|
A more complex example, encoding the AlgorithmIdentifier with
|
|
RSASSA-PSS values.
|
|
|
|
As a reminder, the AlgorithmIdentifier is specified like this:
|
|
|
|
-- From RFC 3280, section 4.1.1.2
|
|
AlgorithmIdentifier ::= SEQUENCE {
|
|
algorithm OBJECT IDENTIFIER,
|
|
parameters ANY DEFINED BY algorithm OPTIONAL }
|
|
|
|
And the RSASSA-PSS OID and parameters are specified like this:
|
|
|
|
-- From RFC 3279, section 3.1
|
|
id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }
|
|
|
|
RSASSA-PSS-params ::= SEQUENCE {
|
|
hashAlgorithm [0] HashAlgorithm DEFAULT
|
|
sha1Identifier,
|
|
maskGenAlgorithm [1] MaskGenAlgorithm DEFAULT
|
|
mgf1SHA1Identifier,
|
|
saltLength [2] INTEGER DEFAULT 20,
|
|
trailerField [3] INTEGER DEFAULT 1 }
|
|
|
|
The value we want to encode, written in ASN.1 syntax:
|
|
|
|
{
|
|
algorithm id-RSASSA-PSS,
|
|
parameters {
|
|
hashAlgorithm sha256Identifier,
|
|
maskGenAlgorithm mgf1SHA256Identifier,
|
|
saltLength 20 -- unnecessarily explicit
|
|
}
|
|
}
|
|
|
|
Assuming that we have precompiled constants for C<id-RSASSA-PSS>,
|
|
C<sha256Identifier> and C<mgf1SHA256Identifier>, the DER writing code
|
|
looks as follows. This is a complete function to write that specific
|
|
value:
|
|
|
|
int DER_w_AlgorithmIdentifier_RSASSA_PSS_special(WPACKET *pkt,
|
|
int tag,
|
|
RSA *rsa)
|
|
{
|
|
return ossl_DER_w_begin_sequence(pkt, tag)
|
|
&& (ossl_DER_w_begin_sequence(pkt, DER_NO_CONTEXT)
|
|
&& ossl_DER_w_ulong(pkt, 2, 20)
|
|
&& ossl_DER_w_precompiled(pkt, 1,
|
|
der_mgf1SHA256Identifier,
|
|
sizeof(der_mgf1SHA256Identifier))
|
|
&& ossl_DER_w_precompiled(pkt, 0,
|
|
der_sha256Identifier,
|
|
sizeof(der_sha256Identifier))
|
|
&& ossl_DER_w_end_sequence(pkt, DER_NO_CONTEXT))
|
|
&& ossl_DER_w_precompiled(pkt, DER_NO_CONTEXT,
|
|
der_id_RSASSA_PSS,
|
|
sizeof(der_id_RSASSA_PSS))
|
|
&& ossl_DER_w_end_sequence(pkt, tag);
|
|
}
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<ossl_DER_w_bn(3)>, L<ossl_DER_w_begin_sequence(3)>,
|
|
L<ossl_DER_w_precompiled(3)>
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
|
|
|
|
Licensed under the Apache License 2.0 (the "License"). You may not use
|
|
this file except in compliance with the License. You can obtain a copy
|
|
in the file LICENSE in the source distribution or at
|
|
L<https://www.openssl.org/source/license.html>.
|
|
|
|
=cut
|