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X509_check_host(3) OpenSSL X509_check_host(3)
X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc -
X.509 certificate matching
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 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
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
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
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
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
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
These functions were added in OpenSSL 1.0.2.
1.0.2h 2016-05-03 X509_check_host(3)