76 lines
2.8 KiB
Plaintext
76 lines
2.8 KiB
Plaintext
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=pod
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=head1 NAME
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SSL_CTX_set_cert_verify_callback - set peer certificate verification procedure
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=head1 SYNOPSIS
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#include <openssl/ssl.h>
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void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *,void *), void *arg);
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=head1 DESCRIPTION
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SSL_CTX_set_cert_verify_callback() sets the verification callback function for
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I<ctx>. SSL objects that are created from I<ctx> inherit the setting valid at
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the time when L<SSL_new(3)|SSL_new(3)> is called.
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=head1 NOTES
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Whenever a certificate is verified during a SSL/TLS handshake, a verification
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function is called. If the application does not explicitly specify a
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verification callback function, the built-in verification function is used.
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If a verification callback I<callback> is specified via
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SSL_CTX_set_cert_verify_callback(), the supplied callback function is called
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instead. By setting I<callback> to NULL, the default behaviour is restored.
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When the verification must be performed, I<callback> will be called with
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the arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The
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argument I<arg> is specified by the application when setting I<callback>.
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I<callback> should return 1 to indicate verification success and 0 to
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indicate verification failure. If SSL_VERIFY_PEER is set and I<callback>
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returns 0, the handshake will fail. As the verification procedure may
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allow to continue the connection in case of failure (by always returning 1)
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the verification result must be set in any case using the B<error>
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member of I<x509_store_ctx> so that the calling application will be informed
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about the detailed result of the verification procedure!
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Within I<x509_store_ctx>, I<callback> has access to the I<verify_callback>
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function set using L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>.
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=head1 WARNINGS
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Do not mix the verification callback described in this function with the
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B<verify_callback> function called during the verification process. The
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latter is set using the L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>
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family of functions.
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Providing a complete verification procedure including certificate purpose
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settings etc is a complex task. The built-in procedure is quite powerful
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and in most cases it should be sufficient to modify its behaviour using
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the B<verify_callback> function.
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=head1 BUGS
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=head1 RETURN VALUES
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SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
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=head1 SEE ALSO
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L<ssl(3)|ssl(3)>, L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>,
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L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
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L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>
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=head1 HISTORY
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Previous to OpenSSL 0.9.7, the I<arg> argument to B<SSL_CTX_set_cert_verify_callback>
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was ignored, and I<callback> was called simply as
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int (*callback)(X509_STORE_CTX *)
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To compile software written for previous versions of OpenSSL, a dummy
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argument will have to be added to I<callback>.
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=cut
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