1=pod
2
3=head1 NAME
4
5SSL_get_shared_sigalgs, SSL_get_sigalgs - get supported signature algorithms
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 int SSL_get_shared_sigalgs(SSL *s, int idx,
12                            int *psign, int *phash, int *psignhash,
13                            unsigned char *rsig, unsigned char *rhash);
14
15 int SSL_get_sigalgs(SSL *s, int idx,
16                     int *psign, int *phash, int *psignhash,
17                     unsigned char *rsig, unsigned char *rhash);
18
19=head1 DESCRIPTION
20
21SSL_get_shared_sigalgs() returns information about the shared signature
22algorithms supported by peer B<s>. The parameter B<idx> indicates the index
23of the shared signature algorithm to return starting from zero. The signature
24algorithm NID is written to B<*psign>, the hash NID to B<*phash> and the
25sign and hash NID to B<*psignhash>. The raw signature and hash values
26are written to B<*rsig> and B<*rhash>.
27
28SSL_get_sigalgs() is similar to SSL_get_shared_sigalgs() except it returns
29information about all signature algorithms supported by B<s> in the order
30they were sent by the peer.
31
32=head1 RETURN VALUES
33
34SSL_get_shared_sigalgs() and SSL_get_sigalgs() return the number of
35signature algorithms or B<0> if the B<idx> parameter is out of range.
36
37=head1 NOTES
38
39These functions are typically called for debugging purposes (to report
40the peer's preferences) or where an application wants finer control over
41certificate selection. Most applications will rely on internal handling
42and will not need to call them.
43
44If an application is only interested in the highest preference shared
45signature algorithm it can just set B<idx> to zero.
46
47Any or all of the parameters B<psign>, B<phash>, B<psignhash>, B<rsig> or
48B<rhash> can be set to B<NULL> if the value is not required. By setting
49them all to B<NULL> and setting B<idx> to zero the total number of
50signature algorithms can be determined: which can be zero.
51
52These functions must be called after the peer has sent a list of supported
53signature algorithms: after a client hello (for servers) or a certificate
54request (for clients). They can (for example) be called in the certificate
55callback.
56
57Only TLS 1.2, TLS 1.3 and DTLS 1.2 currently support signature algorithms.
58If these
59functions are called on an earlier version of TLS or DTLS zero is returned.
60
61The shared signature algorithms returned by SSL_get_shared_sigalgs() are
62ordered according to configuration and peer preferences.
63
64The raw values correspond to the on the wire form as defined by RFC5246 et al.
65The NIDs are OpenSSL equivalents. For example if the peer sent sha256(4) and
66rsa(1) then B<*rhash> would be 4, B<*rsign> 1, B<*phash> NID_sha256, B<*psig>
67NID_rsaEncryption and B<*psignhash> NID_sha256WithRSAEncryption.
68
69If a signature algorithm is not recognised the corresponding NIDs
70will be set to B<NID_undef>. This may be because the value is not supported,
71is not an appropriate combination (for example MD5 and DSA) or the
72signature algorithm does not use a hash (for example Ed25519).
73
74=head1 SEE ALSO
75
76L<SSL_CTX_set_cert_cb(3)>,
77L<ssl(7)>
78
79=head1 COPYRIGHT
80
81Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.
82
83Licensed under the Apache License 2.0 (the "License").  You may not use
84this file except in compliance with the License.  You can obtain a copy
85in the file LICENSE in the source distribution or at
86L<https://www.openssl.org/source/license.html>.
87
88=cut
89