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.