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 host name, 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 host
28name, which 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>.  Only the mailbox syntax of RFC 822 is supported,
52comments are not allowed, and no attempt is made to normalize quoted
53characters.  The B<addresslen> argument must be the number of
54characters in the address string or zero in which case the length
55is calculated with strlen(B<address>).
56
57X509_check_ip() checks if the certificate matches a specified IPv4 or
58IPv6 address.  The B<address> array is in binary format, in network
59byte order.  The length is either 4 (IPv4) or 16 (IPv6).  Only
60explicitly marked addresses in the certificates are considered; IP
61addresses stored in DNS names and Common Names are ignored.
62
63X509_check_ip_asc() is similar, except that the NUL-terminated
64string B<address> is first converted to the internal representation.
65
66The B<flags> argument is usually 0.  It can be the bitwise OR of the
67flags:
68
69=over 4
70
71=item B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT>,
72
73=item B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT>,
74
75=item B<X509_CHECK_FLAG_NO_WILDCARDS>,
76
77=item B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS>,
78
79=item B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>.
80
81=item B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>.
82
83=back
84
85The B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> flag causes the function
86to consider the subject DN even if the certificate contains at least
87one subject alternative name of the right type (DNS name or email
88address as appropriate); the default is to ignore the subject DN
89when at least one corresponding subject alternative names is present.
90
91The B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> flag causes the function to never
92consider the subject DN even if the certificate contains no subject alternative
93names of the right type (DNS name or email address as appropriate); the default
94is to use the subject DN when no corresponding subject alternative names are
95present.
96If both B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> and
97B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> are specified, the latter takes
98precedence and the subject DN is not checked for matching names.
99
100If set, B<X509_CHECK_FLAG_NO_WILDCARDS> disables wildcard
101expansion; this only applies to B<X509_check_host>.
102
103If set, B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS> suppresses support
104for "*" as wildcard pattern in labels that have a prefix or suffix,
105such as: "www*" or "*www"; this only applies to B<X509_check_host>.
106
107If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS> allows a "*" that
108constitutes the complete label of a DNS name (e.g. "*.example.com")
109to match more than one label in B<name>; this flag only applies
110to B<X509_check_host>.
111
112If set, B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> restricts B<name>
113values which start with ".", that would otherwise match any sub-domain
114in the peer certificate, to only match direct child sub-domains.
115Thus, for instance, with this flag set a B<name> of ".example.com"
116would match a peer certificate with a DNS name of "www.example.com",
117but would not match a peer certificate with a DNS name of
118"www.sub.example.com"; this flag only applies to B<X509_check_host>.
119
120=head1 RETURN VALUES
121
122The functions return 1 for a successful match, 0 for a failed match
123and -1 for an internal error: typically a memory allocation failure
124or an ASN.1 decoding error.
125
126All functions can also return -2 if the input is malformed. For example,
127X509_check_host() returns -2 if the provided B<name> contains embedded
128NULs.
129
130=head1 NOTES
131
132Applications are encouraged to use X509_VERIFY_PARAM_set1_host()
133rather than explicitly calling L<X509_check_host(3)>. Host name
134checks may be out of scope with the DANE-EE(3) certificate usage,
135and the internal checks will be suppressed as appropriate when
136DANE support is enabled.
137
138=head1 SEE ALSO
139
140L<SSL_get_verify_result(3)>,
141L<X509_VERIFY_PARAM_set1_host(3)>,
142L<X509_VERIFY_PARAM_add1_host(3)>,
143L<X509_VERIFY_PARAM_set1_email(3)>,
144L<X509_VERIFY_PARAM_set1_ip(3)>,
145L<X509_VERIFY_PARAM_set1_ipasc(3)>
146
147=head1 HISTORY
148
149These functions were added in OpenSSL 1.0.2.
150
151=head1 COPYRIGHT
152
153Copyright 2012-2018 The OpenSSL Project Authors. All Rights Reserved.
154
155Licensed under the OpenSSL license (the "License").  You may not use
156this file except in compliance with the License.  You can obtain a copy
157in the file LICENSE in the source distribution or at
158L<https://www.openssl.org/source/license.html>.
159
160=cut
161