Ubuntu Manpage: X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc

Provided by: libssl-doc_1.0.2g-1ubuntu4.20_all

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.

HISTORY