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.
66
67X509_check_ip_asc() is similar, except that the NUL-terminated
68string B<address> is first converted to the internal representation.
69
70The B<flags> argument is usually 0.  It can be the bitwise OR of the
71flags:
72
73=over 4
74
75=item B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT>,
76
77=item B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT>,
78
79=item B<X509_CHECK_FLAG_NO_WILDCARDS>,
80
81=item B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS>,
82
83=item B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>.
84
85=item B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>.
86
87=back
88
89The B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> flag causes the function
90to consider the subject DN even if the certificate contains at least
91one subject alternative name of the right type (DNS name or email
92address as appropriate); the default is to ignore the subject DN
93when at least one corresponding subject alternative names is present.
94
95The B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> flag causes the function to never
96consider the subject DN even if the certificate contains no subject alternative
97names of the right type (DNS name or email address as appropriate); the default
98is to use the subject DN when no corresponding subject alternative names are
99present.
100If both B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> and
101B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> are specified, the latter takes
102precedence and the subject DN is not checked for matching names.
103
104If set, B<X509_CHECK_FLAG_NO_WILDCARDS> disables wildcard
105expansion; this only applies to B<X509_check_host>.
106
107If set, B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS> suppresses support
108for "*" as wildcard pattern in labels that have a prefix or suffix,
109such as: "www*" or "*www"; this only applies to B<X509_check_host>.
110
111If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS> allows a "*" that
112constitutes the complete label of a DNS name (e.g. "*.example.com")
113to match more than one label in B<name>; this flag only applies
114to B<X509_check_host>.
115
116If set, B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> restricts B<name>
117values which start with ".", that would otherwise match any sub-domain
118in the peer certificate, to only match direct child sub-domains.
119Thus, for instance, with this flag set a B<name> of ".example.com"
120would match a peer certificate with a DNS name of "www.example.com",
121but would not match a peer certificate with a DNS name of
122"www.sub.example.com"; this flag only applies to B<X509_check_host>.
123
124=head1 RETURN VALUES
125
126The functions return 1 for a successful match, 0 for a failed match
127and -1 for an internal error: typically a memory allocation failure
128or an ASN.1 decoding error.
129
130All functions can also return -2 if the input is malformed. For example,
131X509_check_host() returns -2 if the provided B<name> contains embedded
132NULs.
133
134=head1 NOTES
135
136Applications are encouraged to use X509_VERIFY_PARAM_set1_host()
137rather than explicitly calling L<X509_check_host(3)>. Hostname
138checks may be out of scope with the DANE-EE(3) certificate usage,
139and the internal checks will be suppressed as appropriate when
140DANE support is enabled.
141
142=head1 SEE ALSO
143
144L<SSL_get_verify_result(3)>,
145L<X509_VERIFY_PARAM_set1_host(3)>,
146L<X509_VERIFY_PARAM_add1_host(3)>,
147L<X509_VERIFY_PARAM_set1_email(3)>,
148L<X509_VERIFY_PARAM_set1_ip(3)>
149
150=head1 HISTORY
151
152These functions were added in OpenSSL 1.0.2.
153
154=head1 COPYRIGHT
155
156Copyright 2012-2021 The OpenSSL Project Authors. All Rights Reserved.
157
158Licensed under the Apache License 2.0 (the "License").  You may not use
159this file except in compliance with the License.  You can obtain a copy
160in the file LICENSE in the source distribution or at
161L<https://www.openssl.org/source/license.html>.
162
163=cut
164