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X509_check_host(3)                  OpenSSL                 X509_check_host(3)



NAME
       X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc -
       X.509 certificate matching

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/x509v3.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_NEVER_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.

       The X509_CHECK_FLAG_NEVER_CHECK_SUBJECT flag causes the function to
       never consider the subject DN even if the certificate contains no
       subject alternative names of the right type (DNS name or email address
       as appropriate); the default is to use the subject DN when no
       corresponding subject alternative names are present.  If both
       X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT and
       X509_CHECK_FLAG_NEVER_CHECK_SUBJECT are specified, the latter takes
       precedence and the subject DN is not checked for matching names.

       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 applies 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 may be out
       of scope with the DANE-EE(3) certificate usage, and the internal checks
       will be suppressed as appropriate when DANE support is enabled.

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.

COPYRIGHT
       Copyright 2012-2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



1.1.1                             2018-09-17                X509_check_host(3)