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SSL_GET_SHARED_SIGALGS(3)           OpenSSL          SSL_GET_SHARED_SIGALGS(3)
NAME
       SSL_get_shared_sigalgs, SSL_get_sigalgs - get supported signature
       algorithms
SYNOPSIS
        #include <openssl/ssl.h>
        int SSL_get_shared_sigalgs(SSL *s, int idx,
                                   int *psign, int *phash, int *psignhash,
                                   unsigned char *rsig, unsigned char *rhash);
        int SSL_get_sigalgs(SSL *s, int idx,
                            int *psign, int *phash, int *psignhash,
                            unsigned char *rsig, unsigned char *rhash);
DESCRIPTION
       SSL_get_shared_sigalgs() returns information about the shared signature
       algorithms supported by peer s. The parameter idx indicates the index
       of the shared signature algorithm to return starting from zero. The
       signature algorithm NID is written to *psign, the hash NID to *phash
       and the sign and hash NID to *psignhash. The raw signature and hash
       values are written to *rsig and *rhash.
       SSL_get_sigalgs() is similar to SSL_get_shared_sigalgs() except it
       returns information about all signature algorithms supported by s in
       the order they were sent by the peer.
RETURN VALUES
       SSL_get_shared_sigalgs() and SSL_get_sigalgs() return the number of
       signature algorithms or 0 if the idx parameter is out of range.
NOTES
       These functions are typically called for debugging purposes (to report
       the peer's preferences) or where an application wants finer control
       over certificate selection. Most applications will rely on internal
       handling and will not need to call them.
       If an application is only interested in the highest preference shared
       signature algorithm it can just set idx to zero.
       Any or all of the parameters psign, phash, psignhash, rsig or rhash can
       be set to NULL if the value is not required. By setting them all to
       NULL and setting idx to zero the total number of signature algorithms
       can be determined: which can be zero.
       These functions must be called after the peer has sent a list of
       supported signature algorithms: after a client hello (for servers) or a
       certificate request (for clients). They can (for example) be called in
       the certificate callback.
       Only TLS 1.2, TLS 1.3 and DTLS 1.2 currently support signature
       algorithms.  If these functions are called on an earlier version of TLS
       or DTLS zero is returned.
       The shared signature algorithms returned by SSL_get_shared_sigalgs()
       are ordered according to configuration and peer preferences.
       The raw values correspond to the on the wire form as defined by RFC5246
       et al.  The NIDs are OpenSSL equivalents. For example if the peer sent
       sha256(4) and rsa(1) then *rhash would be 4, *rsign 1, *phash
       NID_sha256, *psig NID_rsaEncryption and *psighash
       NID_sha256WithRSAEncryption.
       If a signature algorithm is not recognised the corresponding NIDs will
       be set to NID_undef. This may be because the value is not supported, is
       not an appropriate combination (for example MD5 and DSA) or the
       signature algorithm does not use a hash (for example Ed25519).
SEE ALSO
       SSL_CTX_set_cert_cb(3), ssl(7)
COPYRIGHT
       Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.
       Licensed under the OpenSSL license (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
       <https://www.openssl.org/source/license.html>;.
1.1.1k                            2021-03-25         SSL_GET_SHARED_SIGALGS(3)