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Title "X509_CHECK_HOST 3ossl" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc - X.509 certificate matching Header "SYNOPSIS" .Vb 1 #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); .Ve Header "DESCRIPTION" The certificate matching functions are used to check whether a certificate matches a given hostname, email address, or \s-1IP\s0 address. The validity of the certificate and its trust level has to be checked by other means.

\fBX509_check_host() checks if the certificate Subject Alternative Name (\s-1SAN\s0) or Subject CommonName (\s-1CN\s0) matches the specified hostname, which must be encoded in the preferred name syntax described in section 3.5 of \s-1RFC 1034.\s0 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 \*(L"www.example.com\*(R" would match a certificate with a \s-1SAN\s0 or \s-1CN\s0 value of \*(L"*.example.com\*(R", \*(L"w*.example.com\*(R" or \*(L"*w.example.com\*(R".

Per section 6.4.2 of \s-1RFC 6125,\s0 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. \*(L".example.com\*(R"), it will be matched by a certificate valid for any sub-domain of name, (see also \fBX509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS below).

When the certificate is matched, and peername is not \s-1NULL,\s0 a pointer to a copy of the matching \s-1SAN\s0 or \s-1CN\s0 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.

\fBX509_check_email() checks if the certificate matches the specified email address. The mailbox syntax of \s-1RFC 822\s0 is supported, comments are not allowed, and no attempt is made to normalize quoted characters. The mailbox syntax of \s-1RFC 6531\s0 is supported for SmtpUTF8Mailbox address in subjectAltName according to \s-1RFC 8398,\s0 with similar limitations as for \s-1RFC 822\s0 syntax, and no attempt is made to convert from A-label to U-label before comparison. 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).

\fBX509_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; \s-1IP\s0 addresses stored in \s-1DNS\s0 names and Common Names are ignored. There are currently no flags that would affect the behavior of this call.

\fBX509_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 \s-1OR\s0 of the flags:

Item "X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT,"

0

Item "X509_CHECK_FLAG_NEVER_CHECK_SUBJECT," Item "X509_CHECK_FLAG_NO_WILDCARDS," Item "X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS," Item "X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS." Item "X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS."

The X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT flag causes the function to consider the subject \s-1DN\s0 even if the certificate contains at least one subject alternative name of the right type (\s-1DNS\s0 name or email address as appropriate); the default is to ignore the subject \s-1DN\s0 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 \s-1DN\s0 even if the certificate contains no subject alternative names of the right type (\s-1DNS\s0 name or email address as appropriate); the default is to use the subject \s-1DN\s0 when no corresponding subject alternative names are present. If both X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT and \fBX509_CHECK_FLAG_NEVER_CHECK_SUBJECT are specified, the latter takes precedence and the subject \s-1DN\s0 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 \*(L"*\*(R" as wildcard pattern in labels that have a prefix or suffix, such as: \*(L"www*\*(R" or \*(L"*www\*(R"; this only applies to X509_check_host.

If set, X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS allows a \*(L"*\*(R" that constitutes the complete label of a \s-1DNS\s0 name (e.g. \*(L"*.example.com\*(R") 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 \*(L".\*(R", 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 \*(L".example.com\*(R" would match a peer certificate with a \s-1DNS\s0 name of \*(L"www.example.com\*(R", but would not match a peer certificate with a \s-1DNS\s0 name of \*(L"www.sub.example.com\*(R"; this flag only applies to X509_check_host.

Header "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 \s-1ASN.1\s0 decoding error.

All functions can also return -2 if the input is malformed. For example, \fBX509_check_host() returns -2 if the provided name contains embedded NULs.

Header "NOTES" Applications are encouraged to use X509_VERIFY_PARAM_set1_host() rather than explicitly calling X509_check_host\|(3). Hostname checks may be out of scope with the \s-1DANE-EE\s0\|(3) certificate usage, and the internal checks will be suppressed as appropriate when \s-1DANE\s0 support is enabled. Header "SEE ALSO" \fBSSL_get_verify_result\|(3), \fBX509_VERIFY_PARAM_set1_host\|(3), \fBX509_VERIFY_PARAM_add1_host\|(3), \fBX509_VERIFY_PARAM_set1_email\|(3), \fBX509_VERIFY_PARAM_set1_ip\|(3) Header "HISTORY" These functions were added in OpenSSL 1.0.2. Header "COPYRIGHT" Copyright 2012-2022 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.