doc/man3/SSL_CTX_set_ct_validation_callback.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 ssl_ct_validation_cb,
 SSL_enable_ct, SSL_CTX_enable_ct, SSL_disable_ct, SSL_CTX_disable_ct,
 SSL_set_ct_validation_callback, SSL_CTX_set_ct_validation_callback,
 SSL_ct_is_enabled, SSL_CTX_ct_is_enabled -
 control Certificate Transparency policy

 =head1 SYNOPSIS

  #include <openssl/ssl.h>

  typedef int (*ssl_ct_validation_cb)(const CT_POLICY_EVAL_CTX *ctx,
                                     const STACK_OF(SCT) *scts, void *arg);

  int SSL_enable_ct(SSL *s, int validation_mode);
  int SSL_CTX_enable_ct(SSL_CTX *ctx, int validation_mode);
  int SSL_set_ct_validation_callback(SSL *s, ssl_ct_validation_cb callback,
                                     void *arg);
  int SSL_CTX_set_ct_validation_callback(SSL_CTX *ctx,
                                         ssl_ct_validation_cb callback,
                                         void *arg);
  void SSL_disable_ct(SSL *s);
  void SSL_CTX_disable_ct(SSL_CTX *ctx);
  int SSL_ct_is_enabled(const SSL *s);
  int SSL_CTX_ct_is_enabled(const SSL_CTX *ctx);

 =head1 DESCRIPTION

 SSL_enable_ct() and SSL_CTX_enable_ct() enable the processing of signed
 certificate timestamps (SCTs) either for a given SSL connection or for all
 connections that share the given SSL context, respectively.
 This is accomplished by setting a built-in CT validation callback.
 The behaviour of the callback is determined by the B<validation_mode> argument,
 which can be either of B<SSL_CT_VALIDATION_PERMISSIVE> or
 B<SSL_CT_VALIDATION_STRICT> as described below.

 If B<validation_mode> is equal to B<SSL_CT_VALIDATION_STRICT>, then in a full
 TLS handshake with the verification mode set to B<SSL_VERIFY_PEER>, if the peer
 presents no valid SCTs the handshake will be aborted.
 If the verification mode is B<SSL_VERIFY_NONE>, the handshake will continue
 despite lack of valid SCTs.
 However, in that case if the verification status before the built-in callback
 was B<X509_V_OK> it will be set to B<X509_V_ERR_NO_VALID_SCTS> after the
 callback.
 Applications can call L<SSL_get_verify_result(3)> to check the status at
 handshake completion, even after session resumption since the verification
 status is part of the saved session state.
 See L<SSL_set_verify(3)>, <SSL_get_verify_result(3)>, L<SSL_session_reused(3)>.

 If B<validation_mode> is equal to B<SSL_CT_VALIDATION_PERMISSIVE>, then the
 handshake continues, and the verification status is not modified, regardless of
 the validation status of any SCTs.
 The application can still inspect the validation status of the SCTs at
 handshake completion.
 Note that with session resumption there will not be any SCTs presented during
 the handshake.
 Therefore, in applications that delay SCT policy enforcement until after
 handshake completion, such delayed SCT checks should only be performed when the
 session is not resumed.

 SSL_set_ct_validation_callback() and SSL_CTX_set_ct_validation_callback()
 register a custom callback that may implement a different policy than either of
 the above.
 This callback can examine the peer's SCTs and determine whether they are
 sufficient to allow the connection to continue.
 The TLS handshake is aborted if the verification mode is not B<SSL_VERIFY_NONE>
 and the callback returns a non-positive result.

 An arbitrary callback data argument, B<arg>, can be passed in when setting
 the callback.
 This will be passed to the callback whenever it is invoked.
 Ownership of this context remains with the caller.

 If no callback is set, SCTs will not be requested and Certificate Transparency
 validation will not occur.

 No callback will be invoked when the peer presents no certificate, e.g. by
 employing an anonymous (aNULL) cipher suite.
 In that case the handshake continues as it would had no callback been
 requested.
 Callbacks are also not invoked when the peer certificate chain is invalid or
 validated via DANE-TA(2) or DANE-EE(3) TLSA records which use a private X.509
 PKI, or no X.509 PKI at all, respectively.
 Clients that require SCTs are expected to not have enabled any aNULL ciphers
 nor to have specified server verification via DANE-TA(2) or DANE-EE(3) TLSA
 records.

 SSL_disable_ct() and SSL_CTX_disable_ct() turn off CT processing, whether
 enabled via the built-in or the custom callbacks, by setting a NULL callback.
 These may be implemented as macros.

 SSL_ct_is_enabled() and SSL_CTX_ct_is_enabled() return 1 if CT processing is
 enabled via either SSL_enable_ct() or a non-null custom callback, and 0
 otherwise.

 =head1 NOTES

 When SCT processing is enabled, OCSP stapling will be enabled. This is because
 one possible source of SCTs is the OCSP response from a server.

 The time returned by SSL_SESSION_get_time() will be used to evaluate whether any
 presented SCTs have timestamps that are in the future (and therefore invalid).

 =head1 RESTRICTIONS

 Certificate Transparency validation cannot be enabled and so a callback cannot
 be set if a custom client extension handler has been registered to handle SCT
 extensions (B<TLSEXT_TYPE_signed_certificate_timestamp>).

 =head1 RETURN VALUES

 SSL_enable_ct(), SSL_CTX_enable_ct(), SSL_CTX_set_ct_validation_callback() and
 SSL_set_ct_validation_callback() return 1 if the B<callback> is successfully
 set.
 They return 0 if an error occurs, e.g. a custom client extension handler has
 been setup to handle SCTs.

 SSL_disable_ct() and SSL_CTX_disable_ct() do not return a result.

 SSL_CTX_ct_is_enabled() and SSL_ct_is_enabled() return a 1 if a non-null CT
 validation callback is set, or 0 if no callback (or equivalently a NULL
 callback) is set.

 =head1 SEE ALSO

 L<ssl(7)>,
 <SSL_get_verify_result(3)>,
 L<SSL_session_reused(3)>,
 L<SSL_set_verify(3)>,
 L<SSL_CTX_set_verify(3)>,
 L<SSL_SESSION_get_time(3)>

 =head1 COPYRIGHT

 Copyright 2016-2020 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>.

 =cut
	=pod

	=head1 NAME

	ssl_ct_validation_cb,
	SSL_enable_ct, SSL_CTX_enable_ct, SSL_disable_ct, SSL_CTX_disable_ct,
	SSL_set_ct_validation_callback, SSL_CTX_set_ct_validation_callback,
	SSL_ct_is_enabled, SSL_CTX_ct_is_enabled -
	control Certificate Transparency policy

	=head1 SYNOPSIS

	#include <openssl/ssl.h>

	typedef int (ssl_ct_validation_cb)(const CT_POLICY_EVAL_CTX ctx,
	const STACK_OF(SCT) scts, void arg);

	int SSL_enable_ct(SSL *s, int validation_mode);
	int SSL_CTX_enable_ct(SSL_CTX *ctx, int validation_mode);
	int SSL_set_ct_validation_callback(SSL *s, ssl_ct_validation_cb callback,
	void *arg);
	int SSL_CTX_set_ct_validation_callback(SSL_CTX *ctx,
	ssl_ct_validation_cb callback,
	void *arg);
	void SSL_disable_ct(SSL *s);
	void SSL_CTX_disable_ct(SSL_CTX *ctx);
	int SSL_ct_is_enabled(const SSL *s);
	int SSL_CTX_ct_is_enabled(const SSL_CTX *ctx);

	=head1 DESCRIPTION

	SSL_enable_ct() and SSL_CTX_enable_ct() enable the processing of signed
	certificate timestamps (SCTs) either for a given SSL connection or for all
	connections that share the given SSL context, respectively.
	This is accomplished by setting a built-in CT validation callback.
	The behaviour of the callback is determined by the B<validation_mode> argument,
	which can be either of B<SSL_CT_VALIDATION_PERMISSIVE> or
	B<SSL_CT_VALIDATION_STRICT> as described below.

	If B<validation_mode> is equal to B<SSL_CT_VALIDATION_STRICT>, then in a full
	TLS handshake with the verification mode set to B<SSL_VERIFY_PEER>, if the peer
	presents no valid SCTs the handshake will be aborted.
	If the verification mode is B<SSL_VERIFY_NONE>, the handshake will continue
	despite lack of valid SCTs.
	However, in that case if the verification status before the built-in callback
	was B<X509_V_OK> it will be set to B<X509_V_ERR_NO_VALID_SCTS> after the
	callback.
	Applications can call L<SSL_get_verify_result(3)> to check the status at
	handshake completion, even after session resumption since the verification
	status is part of the saved session state.
	See L<SSL_set_verify(3)>, <SSL_get_verify_result(3)>, L<SSL_session_reused(3)>.

	If B<validation_mode> is equal to B<SSL_CT_VALIDATION_PERMISSIVE>, then the
	handshake continues, and the verification status is not modified, regardless of
	the validation status of any SCTs.
	The application can still inspect the validation status of the SCTs at
	handshake completion.
	Note that with session resumption there will not be any SCTs presented during
	the handshake.
	Therefore, in applications that delay SCT policy enforcement until after
	handshake completion, such delayed SCT checks should only be performed when the
	session is not resumed.

	SSL_set_ct_validation_callback() and SSL_CTX_set_ct_validation_callback()
	register a custom callback that may implement a different policy than either of
	the above.
	This callback can examine the peer's SCTs and determine whether they are
	sufficient to allow the connection to continue.
	The TLS handshake is aborted if the verification mode is not B<SSL_VERIFY_NONE>
	and the callback returns a non-positive result.

	An arbitrary callback data argument, B<arg>, can be passed in when setting
	the callback.
	This will be passed to the callback whenever it is invoked.
	Ownership of this context remains with the caller.

	If no callback is set, SCTs will not be requested and Certificate Transparency
	validation will not occur.

	No callback will be invoked when the peer presents no certificate, e.g. by
	employing an anonymous (aNULL) cipher suite.
	In that case the handshake continues as it would had no callback been
	requested.
	Callbacks are also not invoked when the peer certificate chain is invalid or
	validated via DANE-TA(2) or DANE-EE(3) TLSA records which use a private X.509
	PKI, or no X.509 PKI at all, respectively.
	Clients that require SCTs are expected to not have enabled any aNULL ciphers
	nor to have specified server verification via DANE-TA(2) or DANE-EE(3) TLSA
	records.

	SSL_disable_ct() and SSL_CTX_disable_ct() turn off CT processing, whether
	enabled via the built-in or the custom callbacks, by setting a NULL callback.
	These may be implemented as macros.

	SSL_ct_is_enabled() and SSL_CTX_ct_is_enabled() return 1 if CT processing is
	enabled via either SSL_enable_ct() or a non-null custom callback, and 0
	otherwise.

	=head1 NOTES

	When SCT processing is enabled, OCSP stapling will be enabled. This is because
	one possible source of SCTs is the OCSP response from a server.

	The time returned by SSL_SESSION_get_time() will be used to evaluate whether any
	presented SCTs have timestamps that are in the future (and therefore invalid).

	=head1 RESTRICTIONS

	Certificate Transparency validation cannot be enabled and so a callback cannot
	be set if a custom client extension handler has been registered to handle SCT
	extensions (B<TLSEXT_TYPE_signed_certificate_timestamp>).

	=head1 RETURN VALUES

	SSL_enable_ct(), SSL_CTX_enable_ct(), SSL_CTX_set_ct_validation_callback() and
	SSL_set_ct_validation_callback() return 1 if the B<callback> is successfully
	set.
	They return 0 if an error occurs, e.g. a custom client extension handler has
	been setup to handle SCTs.

	SSL_disable_ct() and SSL_CTX_disable_ct() do not return a result.

	SSL_CTX_ct_is_enabled() and SSL_ct_is_enabled() return a 1 if a non-null CT
	validation callback is set, or 0 if no callback (or equivalently a NULL
	callback) is set.

	=head1 SEE ALSO

	L<ssl(7)>,
	<SSL_get_verify_result(3)>,
	L<SSL_session_reused(3)>,
	L<SSL_set_verify(3)>,
	L<SSL_CTX_set_verify(3)>,
	L<SSL_SESSION_get_time(3)>

	=head1 COPYRIGHT

	Copyright 2016-2020 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>.

	=cut