X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc - X.509
certificate matching
#include <openssl/x509v3.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);
The certificate matching functions are used to check whether a certificate
matches a given hostname, 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 Subject Alternative Name
(SAN) or Subject CommonName (CN) matches the specified hostname, which must be
encoded in the preferred name syntax described in section 3.5 of RFC 1034. By
default, wildcards are supported and they match only in the left-most label;
but they may match part of that label with an explicit prefix or suffix. For
example, by default, the host
name "
www.example.com" would
match a certificate with a SAN or CN value of "*.example.com",
"w*.example.com" or "*w.example.com".
Per section 6.4.2 of RFC 6125,
name values representing international
domain names must be given in A-label form. The
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
name starts with a
dot (e.g. ".example.com"), it will be matched by a certificate valid
for any sub-domain of
name, (see also
X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS below).
When the certificate is matched, and
peername is not NULL, a pointer to a
copy of the matching SAN or CN from the peer certificate is stored at the
address passed in
peername. The application is responsible for freeing
the peername via
OPENSSL_free() when it is no longer needed.
X509_check_email() checks if the certificate matches the specified email
address. The mailbox syntax of RFC 822 is supported, comments are not
allowed, and no attempt is made to normalize quoted characters. The mailbox
syntax of RFC 6531 is supported for SmtpUTF8Mailbox address in subjectAltName
according to RFC 8398, with similar limitations as for RFC 822 syntax, and no
attempt is made to convert from A-label to U-label before comparison. The
addresslen argument must be the number of characters in the address
string or zero in which case the length is calculated with strlen(
address).
X509_check_ip() checks if the certificate matches a specified IPv4 or
IPv6 address. The
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. There are currently no
flags that would
affect the behavior of this call.
X509_check_ip_asc() is similar, except that the NUL-terminated string
address is first converted to the internal representation.
The
flags argument is usually 0. It can be the bitwise OR of the flags:
-
X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT,
-
X509_CHECK_FLAG_NEVER_CHECK_SUBJECT,
-
X509_CHECK_FLAG_NO_WILDCARDS,
-
X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS,
-
X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS.
-
X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS.
The
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.
The
X509_CHECK_FLAG_NEVER_CHECK_SUBJECT flag causes the function to never
consider the subject DN even if the certificate contains no subject
alternative names of the right type (DNS name or email address as
appropriate); the default is to use the subject DN when no corresponding
subject alternative names are present. If both
X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT and
X509_CHECK_FLAG_NEVER_CHECK_SUBJECT are specified, the latter takes
precedence and the subject DN is not checked for matching names.
If set,
X509_CHECK_FLAG_NO_WILDCARDS disables wildcard expansion; this
only applies to
X509_check_host.
If set,
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 applies to
X509_check_host.
If set,
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
name; this flag only applies to
X509_check_host.
If set,
X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS restricts
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
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
X509_check_host.
The functions return 1 for a successful match, 0 for a failed match and -1 for
an internal error: typically a memory allocation failure or an ASN.1 decoding
error.
All functions can also return -2 if the input is malformed. For example,
X509_check_host() returns -2 if the provided
name contains
embedded NULs.
Applications are encouraged to use
X509_VERIFY_PARAM_set1_host() rather
than explicitly calling . Hostname checks may be out
of scope with the
DANE-EE(3) certificate usage, and the internal checks
will be suppressed as appropriate when DANE support is enabled.
SSL_get_verify_result(3),
X509_VERIFY_PARAM_set1_host(3),
X509_VERIFY_PARAM_add1_host(3),
X509_VERIFY_PARAM_set1_email(3),
X509_VERIFY_PARAM_set1_ip(3)
These functions were added in OpenSSL 1.0.2.
Copyright 2012-2022 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy in the
file LICENSE in the source distribution or at
<
https://www.openssl.org/source/license.html>.