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.\"
.IX Title "X509_CMP 3ossl"
.TH X509_CMP 3ossl "2026-01-16" "3.5.1" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
X509_cmp, X509_NAME_cmp,
X509_issuer_and_serial_cmp, X509_issuer_name_cmp, X509_subject_name_cmp,
X509_CRL_cmp, X509_CRL_match
\&\- compare X509 certificates and related values
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/x509.h>
\&
\& int X509_cmp(const X509 *a, const X509 *b);
\& int X509_NAME_cmp(const X509_NAME *a, const X509_NAME *b);
\& int X509_issuer_and_serial_cmp(const X509 *a, const X509 *b);
\& int X509_issuer_name_cmp(const X509 *a, const X509 *b);
\& int X509_subject_name_cmp(const X509 *a, const X509 *b);
\& int X509_CRL_cmp(const X509_CRL *a, const X509_CRL *b);
\& int X509_CRL_match(const X509_CRL *a, const X509_CRL *b);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This set of functions are used to compare X509 objects, including X509
certificates, X509 \s-1CRL\s0 objects and various values in an X509 certificate.
.PP
The \fBX509_cmp()\fR function compares two \fBX509\fR objects indicated by parameters
\&\fIa\fR and \fIb\fR. The comparison is based on the \fBmemcmp\fR result of the hash
values of two \fBX509\fR objects and the canonical (\s-1DER\s0) encoding values.
.PP
The \fBX509_NAME_cmp()\fR function compares two \fBX509_NAME\fR objects indicated by
parameters \fIa\fR and \fIb\fR, any of which may be \s-1NULL.\s0
The comparison is based on the \fBmemcmp\fR result of the
canonical (\s-1DER\s0) encoding values of the two objects using \fBi2d_X509_NAME\fR\|(3).
This procedure adheres to the matching rules for Distinguished Names (\s-1DN\s0)
given in \s-1RFC 4517\s0 section 4.2.15 and \s-1RFC 5280\s0 section 7.1.
In particular, the order of Relative Distinguished Names (RDNs) is relevant.
On the other hand, if an \s-1RDN\s0 is multi-valued, i.e., it contains a set of
AttributeValueAssertions (AVAs), its members are effectively not ordered.
.PP
The \fBX509_issuer_and_serial_cmp()\fR function compares the serial number and issuer
values in the given \fBX509\fR objects \fIa\fR and \fIb\fR.
.PP
The \fBX509_issuer_name_cmp()\fR, \fBX509_subject_name_cmp()\fR and \fBX509_CRL_cmp()\fR functions
are effectively wrappers of the \fBX509_NAME_cmp()\fR function. These functions compare
issuer names and subject names of the  objects, or issuers of \fBX509_CRL\fR
objects, respectively.
.IX Xref "509"
.PP
The \fBX509_CRL_match()\fR function compares two \fBX509_CRL\fR objects. Unlike the
\&\fBX509_CRL_cmp()\fR function, this function compares the whole \s-1CRL\s0 content instead
of just the issuer name.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
The \fBX509\fR comparison functions return \fB\-1\fR, \fB0\fR, or \fB1\fR if object \fIa\fR is
found to be less than, to match, or be greater than object \fIb\fR, respectively.
.PP
\&\fBX509_NAME_cmp()\fR, \fBX509_issuer_and_serial_cmp()\fR, \fBX509_issuer_name_cmp()\fR,
\&\fBX509_subject_name_cmp()\fR, \fBX509_CRL_cmp()\fR, and \fBX509_CRL_match()\fR
may return \fB\-2\fR to indicate an error.
.SH "NOTES"
.IX Header "NOTES"
These functions in fact utilize the underlying \fBmemcmp\fR of the C library to do
the comparison job. Data to be compared varies from \s-1DER\s0 encoding data, hash
value or \fB\s-1ASN1_STRING\s0\fR. The sign of the comparison can be used to order the
objects but it does not have a special meaning in some cases.
.PP
\&\fBX509_NAME_cmp()\fR and wrappers utilize the value \fB\-2\fR to indicate errors in some
circumstances, which could cause confusion for the applications.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBi2d_X509_NAME\fR\|(3), \fBi2d_X509\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2019\-2022 The OpenSSL Project Authors. All Rights Reserved.
.PP
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>.
