X.509 certificate matching
const char *name, size_t
namelen, unsigned int flags,
const char *address, size_t
addresslen, unsigned int flags);
const unsigned char *address, size_t
addresslen, unsigned int flags);
const char *address, unsigned int
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.
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; 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
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
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
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 free(3) when it is no longer needed.
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
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.
is similar, except that the NUL-terminated string
address is first converted to the internal
The flags argument is usually 0, but it can be the bitwise OR of the following flags.
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 remaining flags are only meaningful for
disables wildcard expansion.
flag suppresses support for "*" as a wildcard pattern in labels
that have a prefix or suffix, such as "www*" or
flag allows a "*" that constitutes the complete label of a DNS
name (e.g. "*.example.com") to match more than one label in
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
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
X509_check_host() returns -2 if the
provided name contains embedded NUL bytes.
X509_EXTENSION_new(3), X509_get1_email(3), X509_new(3)
These functions first appeared in OpenSSL 1.0.2 and have been available since OpenBSD 6.1.