openssl/doc/crypto/X509_check_host.pod

=pod

=head1 NAME

X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc - X.509 certificate matching

=head1 SYNOPSIS

 #include <openssl/x509.h>

 int X509_check_host(X509 *, const char *name, size_t namelen,
		     unsigned int flags, char **peername);
 int X509_check_email(X509 *, const char *address, size_t addresslen,
		      unsigned int flags);
 int X509_check_ip(X509 *, const unsigned char *address, size_t addresslen,
		   unsigned int flags);
 int X509_check_ip_asc(X509 *, const char *address, unsigned int flags);

=head1 DESCRIPTION

The certificate matching functions are intended to be called to check
if a certificate matches a given host name, email address, or IP
address.  The validity of the certificate and its trust level has to
be checked by other means.

X509_check_host() checks if the certificate matches the specified
host name, which must be encoded in the preferred name syntax
described in section 3.5 of RFC 1034. Per section 6.4.2 of RFC 6125,
B<name> values representing international domain names must be given
in A-label form.  The B<namelen> argument must be the number of
characters in the name string or zero in which case the length is
calculated with strlen(name).  When B<name> starts with a dot (e.g
".example.com"), it will be matched by a certificate valid for any
sub-domain of B<name>, (see also B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>
below).  When the certificate is matched and B<peername> is not
NULL a pointer to a copy of the matching hostname or CommonName
from the peer certificate is stored at the address passed in
B<peername>.  The application is responsible for freeing the peername
via OPENSSL_free() when it is no longer needed.  Applications are
advised to use X509_VERIFY_PARAM_set1_host() in preference to
explicitly calling L<X509_check_host(3)>, hostname checks are out
of scope with the DANE-EE(3) certificate usage, and the internal
check will be suppressed as appropriate when DANE support is added
to OpenSSL.

X509_check_email() checks if the certificate matches the specified
email address.  Only the mailbox syntax of RFC 822 is supported,
comments are not allowed, and no attempt is made to normalize quoted
characters.  The B<addresslen> argument must be the number of
characters in the address string. The B<namelen> argument must be
the number of characters in the name string or zero in which case the
length is calculated with strlen(name).

X509_check_ip() checks if the certificate matches a specified IPv4 or
IPv6 address.  The B<address> array is in binary format, in network
byte order.  The length is either 4 (IPv4) or 16 (IPv6).  Only
explicitly marked addresses in the certificates are considered; IP
addresses stored in DNS names and Common Names are ignored.

X509_check_ip_asc() is similar, except that the NUL-terminated
string B<address> is first converted to the internal representation.

The B<flags> argument is usually 0.  It can be the bitwise OR of the
flags:

=over 4

=item B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT>,

=item B<X509_CHECK_FLAG_NO_WILDCARDS>,

=item B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS>,

=item B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>.

=item B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>.

=back

The B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> flag causes the function
to consider the subject DN even if the certificate contains at least
one subject alternative name of the right type (DNS name or email
address as appropriate); the default is to ignore the subject DN
when at least one corresponding subject alternative names is present.

If set, B<X509_CHECK_FLAG_NO_WILDCARDS> disables wildcard
expansion; this only applies to B<X509_check_host>.

If set, B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS> suppresses support
for "*" as wildcard pattern in labels that have a prefix or suffix,
such as: "www*" or "*www"; this only aplies to B<X509_check_host>.

If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS> allows a "*" that
constitutes the complete label of a DNS name (e.g. "*.example.com")
to match more than one label in B<name>; this flag only applies
to B<X509_check_host>.

If set, B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> restricts B<name>
values which start with ".", that would otherwise match any sub-domain
in the peer certificate, to only match direct child sub-domains.
Thus, for instance, with this flag set a B<name> of ".example.com"
would match a peer certificate with a DNS name of "www.example.com",
but would not match a peer certificate with a DNS name of
"www.sub.example.com"; this flag only applies to B<X509_check_host>.

=head1 RETURN VALUES

The functions return 1 for a successful match, 0 for a failed match
and -1 for an internal error: typically a memory allocation failure.

X509_check_ip_asc() can also return -2 if the IP address string is malformed.

=head1 SEE ALSO

L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
L<X509_VERIFY_PARAM_set1_host(3)|X509_VERIFY_PARAM_set1_host(3)>,
L<X509_VERIFY_PARAM_add1_host(3)|X509_VERIFY_PARAM_add1_host(3)>,
L<X509_VERIFY_PARAM_set1_email(3)|X509_VERIFY_PARAM_set1_email(3)>,
L<X509_VERIFY_PARAM_set1_ip(3)|X509_VERIFY_PARAM_set1_ip(3)>,
L<X509_VERIFY_PARAM_set1_ipasc(3)|X509_VERIFY_PARAM_set1_ipasc(3)>

=head1 HISTORY

These functions were added in OpenSSL 1.1.0.

=cut