| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | X509_check_host, X509_check_email, X509_check_ip, X509_check_ip_asc - X.509 certificate matching
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| 6 |
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| 7 | =head1 SYNOPSIS
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| 8 |
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| 9 | #include <openssl/x509v3.h>
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| 10 |
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| 11 | int X509_check_host(X509 *, const char *name, size_t namelen,
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| 12 | unsigned int flags, char **peername);
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| 13 | int X509_check_email(X509 *, const char *address, size_t addresslen,
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| 14 | unsigned int flags);
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| 15 | int X509_check_ip(X509 *, const unsigned char *address, size_t addresslen,
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| 16 | unsigned int flags);
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| 17 | int X509_check_ip_asc(X509 *, const char *address, unsigned int flags);
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| 18 |
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| 19 | =head1 DESCRIPTION
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| 20 |
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| 21 | The certificate matching functions are used to check whether a
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| 22 | certificate matches a given hostname, email address, or IP address.
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| 23 | The validity of the certificate and its trust level has to be checked by
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| 24 | other means.
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| 25 |
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| 26 | X509_check_host() checks if the certificate Subject Alternative
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| 27 | Name (SAN) or Subject CommonName (CN) matches the specified hostname,
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| 28 | which must be encoded in the preferred name syntax described
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| 29 | in section 3.5 of RFC 1034. By default, wildcards are supported
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| 30 | and they match only in the left-most label; but they may match
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| 31 | part of that label with an explicit prefix or suffix. For example,
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| 32 | by default, the host B<name> "www.example.com" would match a
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| 33 | certificate with a SAN or CN value of "*.example.com", "w*.example.com"
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| 34 | or "*w.example.com".
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| 35 |
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| 36 | Per section 6.4.2 of RFC 6125, B<name> values representing international
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| 37 | domain names must be given in A-label form. The B<namelen> argument
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| 38 | must be the number of characters in the name string or zero in which
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| 39 | case the length is calculated with strlen(B<name>). When B<name> starts
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| 40 | with a dot (e.g. ".example.com"), it will be matched by a certificate
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| 41 | valid for any sub-domain of B<name>, (see also
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| 42 | B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> below).
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| 43 |
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| 44 | When the certificate is matched, and B<peername> is not NULL, a
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| 45 | pointer to a copy of the matching SAN or CN from the peer certificate
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| 46 | is stored at the address passed in B<peername>. The application
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| 47 | is responsible for freeing the peername via OPENSSL_free() when it
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| 48 | is no longer needed.
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| 49 |
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| 50 | X509_check_email() checks if the certificate matches the specified
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| 51 | email B<address>. The mailbox syntax of RFC 822 is supported,
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| 52 | comments are not allowed, and no attempt is made to normalize quoted
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| 53 | characters. The mailbox syntax of RFC 6531 is supported for
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| 54 | SmtpUTF8Mailbox address in subjectAltName according to RFC 8398,
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| 55 | with similar limitations as for RFC 822 syntax, and no attempt
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| 56 | is made to convert from A-label to U-label before comparison.
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| 57 | The B<addresslen> argument must be the number of
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| 58 | characters in the address string or zero in which case the length
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| 59 | is calculated with strlen(B<address>).
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| 60 |
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| 61 | X509_check_ip() checks if the certificate matches a specified IPv4 or
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| 62 | IPv6 address. The B<address> array is in binary format, in network
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| 63 | byte order. The length is either 4 (IPv4) or 16 (IPv6). Only
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| 64 | explicitly marked addresses in the certificates are considered; IP
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| 65 | addresses stored in DNS names and Common Names are ignored.
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| 66 |
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| 67 | X509_check_ip_asc() is similar, except that the NUL-terminated
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| 68 | string B<address> is first converted to the internal representation.
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| 69 |
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| 70 | The B<flags> argument is usually 0. It can be the bitwise OR of the
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| 71 | flags:
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| 72 |
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| 73 | =over 4
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| 74 |
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| 75 | =item B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT>,
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| 76 |
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| 77 | =item B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT>,
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| 78 |
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| 79 | =item B<X509_CHECK_FLAG_NO_WILDCARDS>,
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| 80 |
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| 81 | =item B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS>,
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| 82 |
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| 83 | =item B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS>.
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| 84 |
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| 85 | =item B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS>.
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| 86 |
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| 87 | =back
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| 88 |
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| 89 | The B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> flag causes the function
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| 90 | to consider the subject DN even if the certificate contains at least
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| 91 | one subject alternative name of the right type (DNS name or email
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| 92 | address as appropriate); the default is to ignore the subject DN
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| 93 | when at least one corresponding subject alternative names is present.
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| 94 |
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| 95 | The B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> flag causes the function to never
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| 96 | consider the subject DN even if the certificate contains no subject alternative
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| 97 | names of the right type (DNS name or email address as appropriate); the default
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| 98 | is to use the subject DN when no corresponding subject alternative names are
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| 99 | present.
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| 100 | If both B<X509_CHECK_FLAG_ALWAYS_CHECK_SUBJECT> and
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| 101 | B<X509_CHECK_FLAG_NEVER_CHECK_SUBJECT> are specified, the latter takes
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| 102 | precedence and the subject DN is not checked for matching names.
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| 103 |
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| 104 | If set, B<X509_CHECK_FLAG_NO_WILDCARDS> disables wildcard
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| 105 | expansion; this only applies to B<X509_check_host>.
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| 106 |
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| 107 | If set, B<X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS> suppresses support
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| 108 | for "*" as wildcard pattern in labels that have a prefix or suffix,
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| 109 | such as: "www*" or "*www"; this only applies to B<X509_check_host>.
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| 110 |
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| 111 | If set, B<X509_CHECK_FLAG_MULTI_LABEL_WILDCARDS> allows a "*" that
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| 112 | constitutes the complete label of a DNS name (e.g. "*.example.com")
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| 113 | to match more than one label in B<name>; this flag only applies
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| 114 | to B<X509_check_host>.
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| 115 |
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| 116 | If set, B<X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS> restricts B<name>
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| 117 | values which start with ".", that would otherwise match any sub-domain
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| 118 | in the peer certificate, to only match direct child sub-domains.
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| 119 | Thus, for instance, with this flag set a B<name> of ".example.com"
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| 120 | would match a peer certificate with a DNS name of "www.example.com",
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| 121 | but would not match a peer certificate with a DNS name of
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| 122 | "www.sub.example.com"; this flag only applies to B<X509_check_host>.
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| 123 |
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| 124 | =head1 RETURN VALUES
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| 125 |
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| 126 | The functions return 1 for a successful match, 0 for a failed match
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| 127 | and -1 for an internal error: typically a memory allocation failure
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| 128 | or an ASN.1 decoding error.
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| 129 |
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| 130 | All functions can also return -2 if the input is malformed. For example,
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| 131 | X509_check_host() returns -2 if the provided B<name> contains embedded
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| 132 | NULs.
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| 133 |
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| 134 | =head1 NOTES
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| 135 |
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| 136 | Applications are encouraged to use X509_VERIFY_PARAM_set1_host()
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| 137 | rather than explicitly calling L<X509_check_host(3)>. Hostname
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| 138 | checks may be out of scope with the DANE-EE(3) certificate usage,
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| 139 | and the internal checks will be suppressed as appropriate when
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| 140 | DANE support is enabled.
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| 141 |
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| 142 | =head1 SEE ALSO
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| 143 |
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| 144 | L<SSL_get_verify_result(3)>,
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| 145 | L<X509_VERIFY_PARAM_set1_host(3)>,
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| 146 | L<X509_VERIFY_PARAM_add1_host(3)>,
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| 147 | L<X509_VERIFY_PARAM_set1_email(3)>,
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| 148 | L<X509_VERIFY_PARAM_set1_ip(3)>
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| 149 |
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| 150 | =head1 HISTORY
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| 151 |
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| 152 | These functions were added in OpenSSL 1.0.2.
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| 153 |
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| 154 | =head1 COPYRIGHT
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| 155 |
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| 156 | Copyright 2012-2021 The OpenSSL Project Authors. All Rights Reserved.
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| 157 |
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| 158 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 159 | this file except in compliance with the License. You can obtain a copy
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| 160 | in the file LICENSE in the source distribution or at
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| 161 | L<https://www.openssl.org/source/license.html>.
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| 162 |
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| 163 | =cut
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