1=pod
2
3=head1 NAME
4
5SSL_CTX_set_cert_verify_callback - set peer certificate verification procedure
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *,void *), void *arg);
12
13=head1 DESCRIPTION
14
15SSL_CTX_set_cert_verify_callback() sets the verification callback function for
16I<ctx>. SSL objects that are created from I<ctx> inherit the setting valid at
17the time when L<SSL_new(3)|SSL_new(3)> is called.
18
19=head1 NOTES
20
21Whenever a certificate is verified during a SSL/TLS handshake, a verification
22function is called. If the application does not explicitly specify a
23verification callback function, the built-in verification function is used.
24If a verification callback I<callback> is specified via
25SSL_CTX_set_cert_verify_callback(), the supplied callback function is called
26instead. By setting I<callback> to NULL, the default behaviour is restored.
27
28When the verification must be performed, I<callback> will be called with
29the arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The
30argument I<arg> is specified by the application when setting I<callback>.
31
32I<callback> should return 1 to indicate verification success and 0 to
33indicate verification failure. If SSL_VERIFY_PEER is set and I<callback>
34returns 0, the handshake will fail. As the verification procedure may
35allow to continue the connection in case of failure (by always returning 1)
36the verification result must be set in any case using the B<error>
37member of I<x509_store_ctx> so that the calling application will be informed
38about the detailed result of the verification procedure!
39
40Within I<x509_store_ctx>, I<callback> has access to the I<verify_callback>
41function set using L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>.
42
43=head1 WARNINGS
44
45Do not mix the verification callback described in this function with the
46B<verify_callback> function called during the verification process. The
47latter is set using the L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>
48family of functions.
49
50Providing a complete verification procedure including certificate purpose
51settings etc is a complex task. The built-in procedure is quite powerful
52and in most cases it should be sufficient to modify its behaviour using
53the B<verify_callback> function.
54
55=head1 BUGS
56
57=head1 RETURN VALUES
58
59SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
60
61=head1 SEE ALSO
62
63L<ssl(3)|ssl(3)>, L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>,
64L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
65L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>
66
67=head1 HISTORY
68
69Previous to OpenSSL 0.9.7, the I<arg> argument to B<SSL_CTX_set_cert_verify_callback>
70was ignored, and I<callback> was called simply as
71 int (*callback)(X509_STORE_CTX *)
72To compile software written for previous versions of OpenSSL, a dummy
73argument will have to be added to I<callback>.
74
75=cut
76