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=head1 NAME

X509_verify_cert - discover and verify X509 certificate chain

=head1 SYNOPSIS

 #include <openssl/x509.h>

 int X509_verify_cert(X509_STORE_CTX *ctx);

=head1 DESCRIPTION

The X509_verify_cert() function attempts to discover and validate a
certificate chain based on parameters in B<ctx>.
The verification context, of type B<X509_STORE_CTX>, can be constructed
using L<X509_STORE_CTX_new(3)> and L<X509_STORE_CTX_init(3)>.
It usually includes a set of certificates serving as trust anchors,
a set of non-trusted certificates that may be needed for chain construction,
flags such as X509_V_FLAG_X509_STRICT, and various other optional components
such as a callback function that allows customizing the verification outcome.
A complete description of the certificate verification process is contained in
the L<openssl-verification-options(1)> manual page.

Applications rarely call this function directly but it is used by
OpenSSL internally for certificate validation, in both the S/MIME and
SSL/TLS code.

A negative return value from X509_verify_cert() can occur if it is invoked
incorrectly, such as with no certificate set in B<ctx>, or when it is called
twice in succession without reinitialising B<ctx> for the second call.
A negative return value can also happen due to internal resource problems or if
a retry operation is requested during internal lookups (which never happens
with standard lookup methods).
Applications must check for <= 0 return value on error.

=head1 RETURN VALUES

If a complete chain can be built and validated this function returns 1,
otherwise it return zero, in exceptional circumstances it can also
return a negative code.

If the function fails additional error information can be obtained by
examining B<ctx> using, for example L<X509_STORE_CTX_get_error(3)>.

=head1 BUGS

This function uses the header F<< <openssl/x509.h> >>
as opposed to most chain verification
functions which use F<< <openssl/x509_vfy.h> >>.

=head1 SEE ALSO

L<X509_STORE_CTX_new(3)>, L<X509_STORE_CTX_init(3)>,
L<X509_STORE_CTX_get_error(3)>

=head1 COPYRIGHT

Copyright 2009-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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
L<https://www.openssl.org/source/license.html>.

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