1=pod
2
3=head1 NAME
4
5SSL_check_chain - check certificate chain suitability
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 int SSL_check_chain(SSL *s, X509 *x, EVP_PKEY *pk, STACK_OF(X509) *chain);
12
13=head1 DESCRIPTION
14
15SSL_check_chain() checks whether certificate B<x>, private key B<pk> and
16certificate chain B<chain> is suitable for use with the current session
17B<s>.
18
19=head1 RETURN VALUES
20
21SSL_check_chain() returns a bitmap of flags indicating the validity of the
22chain.
23
24B<CERT_PKEY_VALID>: the chain can be used with the current session.
25If this flag is B<not> set then the certificate will never be used even
26if the application tries to set it because it is inconsistent with the
27peer preferences.
28
29B<CERT_PKEY_SIGN>: the EE key can be used for signing.
30
31B<CERT_PKEY_EE_SIGNATURE>: the signature algorithm of the EE certificate is
32acceptable.
33
34B<CERT_PKEY_CA_SIGNATURE>: the signature algorithms of all CA certificates
35are acceptable.
36
37B<CERT_PKEY_EE_PARAM>: the parameters of the end entity certificate are
38acceptable (e.g. it is a supported curve).
39
40B<CERT_PKEY_CA_PARAM>: the parameters of all CA certificates are acceptable.
41
42B<CERT_PKEY_EXPLICIT_SIGN>: the end entity certificate algorithm
43can be used explicitly for signing (i.e. it is mentioned in the signature
44algorithms extension).
45
46B<CERT_PKEY_ISSUER_NAME>: the issuer name is acceptable. This is only
47meaningful for client authentication.
48
49B<CERT_PKEY_CERT_TYPE>: the certificate type is acceptable. Only meaningful
50for client authentication.
51
52B<CERT_PKEY_SUITEB>: chain is suitable for Suite B use.
53
54=head1 NOTES
55
56SSL_check_chain() must be called in servers after a client hello message or in
57clients after a certificate request message. It will typically be called
58in the certificate callback.
59
60An application wishing to support multiple certificate chains may call this
61function on each chain in turn: starting with the one it considers the
62most secure. It could then use the chain of the first set which returns
63suitable flags.
64
65As a minimum the flag B<CERT_PKEY_VALID> must be set for a chain to be
66usable. An application supporting multiple chains with different CA signature
67algorithms may also wish to check B<CERT_PKEY_CA_SIGNATURE> too. If no
68chain is suitable a server should fall back to the most secure chain which
69sets B<CERT_PKEY_VALID>.
70
71The validity of a chain is determined by checking if it matches a supported
72signature algorithm, supported curves and in the case of client authentication
73certificate types and issuer names.
74
75Since the supported signature algorithms extension is only used in TLS 1.2,
76TLS 1.3 and DTLS 1.2 the results for earlier versions of TLS and DTLS may not
77be very useful. Applications may wish to specify a different "legacy" chain
78for earlier versions of TLS or DTLS.
79
80=head1 SEE ALSO
81
82L<SSL_CTX_set_cert_cb(3)>,
83L<ssl(7)>
84
85=head1 COPYRIGHT
86
87Copyright 2015-2018 The OpenSSL Project Authors. All Rights Reserved.
88
89Licensed under the Apache License 2.0 (the "License").  You may not use
90this file except in compliance with the License.  You can obtain a copy
91in the file LICENSE in the source distribution or at
92L<https://www.openssl.org/source/license.html>.
93
94=cut
95