X509_check_host
Section: OpenSSL (3)
Updated: 2017-05-25
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NAME
X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc - X.509 certificate matching
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);
DESCRIPTION
The certificate matching functions are used to check whether 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 Subject Alternative
Name (SAN) or Subject CommonName (CN) matches the specified host
name, 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. Only the mailbox syntax of RFC 822 is supported,
comments are not allowed, and no attempt is made to normalize quoted
characters. 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.
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_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.
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 aplies 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.
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
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.
NOTES
Applications are encouraged to use
X509_VERIFY_PARAM_set1_host()
rather than explicitly calling
X509_check_host(3). Host name
checks are out of scope with the
DANE-EE(3) certificate usage,
and the internal checks will be suppressed as appropriate when
DANE support is added to OpenSSL.
SEE ALSO
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),
X509_VERIFY_PARAM_set1_ipasc(3)
HISTORY
These functions were added in OpenSSL 1.0.2.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUES
-
- NOTES
-
- SEE ALSO
-
- HISTORY
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