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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 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 <https://www.openssl.org/source/license.html>.