5 SSL_CTX_set_cert_verify_callback - set peer certificate verification procedure
9 #include <openssl/ssl.h>
11 void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(),
17 SSL_CTX_set_cert_verify_callback() sets the verification callback function for
18 B<ctx>. SSL objects, that are created from B<ctx> inherit the setting valid at
19 the time, L<SSL_new(3)|SSL_new(3)> is called. B<arg> is currently ignored.
23 Whenever a certificate is verified during a SSL/TLS handshake, a verification
24 function is called. If the application does not explicitly specify a
25 verification callback function, the built-in verification function is used.
26 If a verification callback B<callback> is specified via
27 SSL_CTX_set_cert_verify_callback(), the supplied callback function is called
28 instead. By setting B<callback> to NULL, the default behaviour is restored.
30 When the verification must be performed, B<callback> will be called with
31 the argument callback(X509_STORE_CTX *x509_store_ctx). The arguments B<arg>
32 that can be specified when setting B<callback> are currently ignored.
34 B<callback> should return 1 to indicate verification success and 0 to
35 indicate verification failure. If SSL_VERIFY_PEER is set and B<callback>
36 returns 0, the handshake will fail. As the verification procedure may
37 allow to continue the connection in case of failure (by always returning 1)
38 the verification result must be set in any case using the B<error>
39 member of B<x509_store_ctx>, so that the calling application will be informed
40 about the detailed result of the verification procedure!
42 Within B<x509_store_ctx>, B<callback> has access to the B<verify_callback>
43 function set using L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>.
47 Do not mix the verification callback described in this function with the
48 B<verify_callback> function called during the verification process. The
49 latter is set using the L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>
52 Providing a complete verification procedure including certificate purpose
53 settings etc is a complex task. The built-in procedure is quite powerful
54 and in most cases it should be sufficient to modify its behaviour using
55 the B<verify_callback> function.
59 It is possible to specify arguments to be passed to the verification callback.
60 Currently they are however not passed but ignored.
62 The B<callback> function is not specified via a prototype, so that no
63 type checking takes place.
67 SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
71 L<ssl(3)|ssl(3)>, L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>,
72 L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
73 L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>