.\" $OpenBSD: X509_check_host.3,v 1.6 2020/09/17 08:04:22 schwarze Exp $ .\" full merge up to: OpenSSL a09e4d24 Jun 12 01:56:31 2014 -0400 .\" selective merge up to: OpenSSL 6328d367 Jul 4 21:58:30 2020 +0200 .\" .\" This file was written by Florian Weimer and .\" Viktor Dukhovni . .\" Copyright (c) 2012, 2014, 2015, 2016 The OpenSSL Project. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: September 17 2020 $ .Dt X509_CHECK_HOST 3 .Os .Sh NAME .Nm X509_check_host , .Nm X509_check_email , .Nm X509_check_ip , .Nm X509_check_ip_asc .Nd X.509 certificate matching .Sh SYNOPSIS .In openssl/x509v3.h .Ft int .Fo X509_check_host .Fa "X509 *x" .Fa "const char *name" .Fa "size_t namelen" .Fa "unsigned int flags" .Fa "char **peername" .Fc .Ft int .Fo X509_check_email .Fa "X509 *x" .Fa "const char *address" .Fa "size_t addresslen" .Fa "unsigned int flags" .Fc .Ft int .Fo X509_check_ip .Fa "X509 *x" .Fa "const unsigned char *address" .Fa "size_t addresslen" .Fa "unsigned int flags" .Fc .Ft int .Fo X509_check_ip_asc .Fa "X509 *x" .Fa "const char *address" .Fa "unsigned int flags" .Fc .Sh DESCRIPTION The certificate matching functions are used to check whether a certificate matches a given hostname, email address, or IP address. The validity of the certificate and its trust level has to be checked by other means. .Pp .Fn X509_check_host checks if the certificate Subject Alternative Name (SAN) or Subject CommonName (CN) matches the specified hostname, 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 .Fa name .Qq www.example.com would match a certificate with a SAN or CN value of .Qq *.example.com , .Qq w*.example.com or .Qq *w.example.com . .Pp Per section 6.4.2 of RFC 6125, .Fa name values representing international domain names must be given in A-label form. The .Fa namelen argument must be the number of characters in the name string or zero, in which case the length is calculated with .Fn strlen name . When .Fa name starts with a dot (e.g.\& .Qq .example.com ) , it will be matched by a certificate valid for any sub-domain of .Fa name ; see also .Fa X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS below. .Pp When the certificate is matched and .Fa peername is not .Dv NULL , a pointer to a copy of the matching SAN or CN from the peer certificate is stored at the address passed in .Fa peername . The application is responsible for freeing the peername via .Xr free 3 when it is no longer needed. .Pp .Fn X509_check_email checks if the certificate matches the specified email .Fa address . Only the mailbox syntax of RFC 822 is supported. Comments are not allowed, and no attempt is made to normalize quoted characters. The .Fa addresslen argument must be the number of characters in the address string or zero, in which case the length is calculated with .Fn strlen address . .Pp .Fn X509_check_ip checks if the certificate matches a specified IPv4 or IPv6 address. The .Fa 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. .Pp .Fn X509_check_ip_asc is similar, except that the NUL-terminated string .Fa address is first converted to the internal representation. .Pp The .Fa flags argument is usually 0, but it can be the bitwise OR of the following flags. .Pp The .Dv 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. .Pp The remaining flags are only meaningful for .Fn X509_check_host . .Pp The .Dv X509_CHECK_FLAG_NO_WILDCARDS flag disables wildcard expansion. .Pp The .Dv X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS flag suppresses support for .Qq * as a wildcard pattern in labels that have a prefix or suffix, such as .Qq www* or .Qq *www . .Pp The .Dv X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS flag allows a .Qq * that constitutes the complete label of a DNS name (e.g.\& .Qq *.example.com ) to match more than one label in .Fa name . .Pp The .Dv X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS flag restricts .Fa name values which start with .Qq \&. , 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 .Fa name of .Qq .example.com would match a peer certificate with a DNS name of .Qq www.example.com , but would not match a peer certificate with a DNS name of .Qq www.sub.example.com . .Sh 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. .Pp All functions can also return -2 if the input is malformed. For example, .Fn X509_check_host returns -2 if the provided .Fa name contains embedded NUL bytes. .Sh SEE ALSO .Xr SSL_set1_host 3 , .Xr X509_EXTENSION_new 3 , .Xr X509_get1_email 3 , .Xr X509_new 3 , .Xr X509_VERIFY_PARAM_set1_host 3 .Sh HISTORY These functions first appeared in OpenSSL 1.0.2 and have been available since .Ox 6.1 .