1=pod
2
3=head1 NAME
4
5X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc - X.509 certificate matching
6
7=head1 SYNOPSIS
8
9 #include <openssl/x509v3.h>
10
11 int X509_check_host(X509 *, const char *name, size_t namelen,
12                     unsigned int flags, char **peername);
13 int X509_check_email(X509 *, const char *address, size_t addresslen,
14                      unsigned int flags);
15 int X509_check_ip(X509 *, const unsigned char *address, size_t addresslen,
16                   unsigned int flags);
17 int X509_check_ip_asc(X509 *, const char *address, unsigned int flags);
18
19=head1 DESCRIPTION
20
21The certificate matching functions are used to check whether a
22certificate matches a given hostname, email address, or IP address.
23The validity of the certificate and its trust level has to be checked by
24other means.
25
26X509_check_host() checks if the certificate Subject Alternative
27Name (SAN) or Subject CommonName (CN) matches the specified hostname,
28which must be encoded in the preferred name syntax described
29in section 3.5 of RFC 1034.  By default, wildcards are supported
30and they match  only in the left-most label; but they may match
31part of that label with an explicit prefix or suffix.  For example,
32by default, the host B<name> "www.example.com" would match a
33certificate with a SAN or CN value of "*.example.com", "w*.example.com"
34or "*w.example.com".
35
36Per section 6.4.2 of RFC 6125, B<name> values representing international
37domain names must be given in A-label form.  The B<namelen> argument
38must be the number of characters in the name string or zero in which
39case the length is calculated with strlen(B<name>).  When B<name> starts
40with a dot (e.g. ".example.com"), it will be matched by a certificate
41valid for any sub-domain of B<name>, (see also
42B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> below).
43
44When the certificate is matched, and B<peername> is not NULL, a
45pointer to a copy of the matching SAN or CN from the peer certificate
46is stored at the address passed in B<peername>.  The application
47is responsible for freeing the peername via OPENSSL_free() when it
48is no longer needed.
49
50X509_check_email() checks if the certificate matches the specified
51email B<address>. The mailbox syntax of RFC 822 is supported,
52comments are not allowed, and no attempt is made to normalize quoted
53characters. The mailbox syntax of RFC 6531 is supported for
54SmtpUTF8Mailbox address in subjectAltName according to RFC 8398,
55with similar limitations as for RFC 822 syntax, and no attempt
56is made to convert from A-label to U-label before comparison.
57The B<addresslen> argument must be the number of
58characters in the address string or zero in which case the length
59is calculated with strlen(B<address>).
60
61X509_check_ip() checks if the certificate matches a specified IPv4 or
62IPv6 address.  The B<address> array is in binary format, in network
63byte order.  The length is either 4 (IPv4) or 16 (IPv6).  Only
64explicitly marked addresses in the certificates are considered; IP
65addresses stored in DNS names and Common Names are ignored. There are
66currently no B<flags> that would affect the behavior of this call.
67
68X509_check_ip_asc() is similar, except that the NUL-terminated
69string B<address> is first converted to the internal representation.
70
71The B<flags> argument is usually 0.  It can be the bitwise OR of the
72flags:
73
74=over 4
75
76=item B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT>,
77
78=item B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT>,
79
80=item B<X509_CHECK_FLAG_NO_WILDCARDS>,
81
82=item B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS>,
83
84=item B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>.
85
86=item B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>.
87
88=back
89
90The B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> flag causes the function
91to consider the subject DN even if the certificate contains at least
92one subject alternative name of the right type (DNS name or email
93address as appropriate); the default is to ignore the subject DN
94when at least one corresponding subject alternative names is present.
95
96The B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> flag causes the function to never
97consider the subject DN even if the certificate contains no subject alternative
98names of the right type (DNS name or email address as appropriate); the default
99is to use the subject DN when no corresponding subject alternative names are
100present.
101If both B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> and
102B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> are specified, the latter takes
103precedence and the subject DN is not checked for matching names.
104
105If set, B<X509_CHECK_FLAG_NO_WILDCARDS> disables wildcard
106expansion; this only applies to B<X509_check_host>.
107
108If set, B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS> suppresses support
109for "*" as wildcard pattern in labels that have a prefix or suffix,
110such as: "www*" or "*www"; this only applies to B<X509_check_host>.
111
112If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS> allows a "*" that
113constitutes the complete label of a DNS name (e.g. "*.example.com")
114to match more than one label in B<name>; this flag only applies
115to B<X509_check_host>.
116
117If set, B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> restricts B<name>
118values which start with ".", that would otherwise match any sub-domain
119in the peer certificate, to only match direct child sub-domains.
120Thus, for instance, with this flag set a B<name> of ".example.com"
121would match a peer certificate with a DNS name of "www.example.com",
122but would not match a peer certificate with a DNS name of
123"www.sub.example.com"; this flag only applies to B<X509_check_host>.
124
125=head1 RETURN VALUES
126
127The functions return 1 for a successful match, 0 for a failed match
128and -1 for an internal error: typically a memory allocation failure
129or an ASN.1 decoding error.
130
131All functions can also return -2 if the input is malformed. For example,
132X509_check_host() returns -2 if the provided B<name> contains embedded
133NULs.
134
135=head1 NOTES
136
137Applications are encouraged to use X509_VERIFY_PARAM_set1_host()
138rather than explicitly calling L<X509_check_host(3)>. Hostname
139checks may be out of scope with the DANE-EE(3) certificate usage,
140and the internal checks will be suppressed as appropriate when
141DANE support is enabled.
142
143=head1 SEE ALSO
144
145L<SSL_get_verify_result(3)>,
146L<X509_VERIFY_PARAM_set1_host(3)>,
147L<X509_VERIFY_PARAM_add1_host(3)>,
148L<X509_VERIFY_PARAM_set1_email(3)>,
149L<X509_VERIFY_PARAM_set1_ip(3)>
150
151=head1 HISTORY
152
153These functions were added in OpenSSL 1.0.2.
154
155=head1 COPYRIGHT
156
157Copyright 2012-2022 The OpenSSL Project Authors. All Rights Reserved.
158
159Licensed under the Apache License 2.0 (the "License").  You may not use
160this file except in compliance with the License.  You can obtain a copy
161in the file LICENSE in the source distribution or at
162L<https://www.openssl.org/source/license.html>.
163
164=cut
165