doc/ssl/SSL_CTX_set_options.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

 SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options,
 SSL_clear_options, SSL_CTX_get_options, SSL_get_options,
 SSL_get_secure_renegotiation_support - manipulate SSL options

 =head1 SYNOPSIS

  #include <openssl/ssl.h>

  long SSL_CTX_set_options(SSL_CTX *ctx, long options);
  long SSL_set_options(SSL *ssl, long options);

  long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
  long SSL_clear_options(SSL *ssl, long options);

  long SSL_CTX_get_options(SSL_CTX *ctx);
  long SSL_get_options(SSL *ssl);

  long SSL_get_secure_renegotiation_support(SSL *ssl);

 =head1 DESCRIPTION

 SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>.
 Options already set before are not cleared!

 SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>.
 Options already set before are not cleared!

 SSL_CTX_clear_options() clears the options set via bitmask in B<options>
 to B<ctx>.

 SSL_clear_options() clears the options set via bitmask in B<options> to B<ssl>.

 SSL_CTX_get_options() returns the options set for B<ctx>.

 SSL_get_options() returns the options set for B<ssl>.

 SSL_get_secure_renegotiation_support() indicates whether the peer supports
 secure renegotiation.
 Note, this is implemented via a macro.

 =head1 NOTES

 The behaviour of the SSL library can be changed by setting several options.
 The options are coded as bitmasks and can be combined by a bitwise B<or>
 operation (|).

 SSL_CTX_set_options() and SSL_set_options() affect the (external)
 protocol behaviour of the SSL library. The (internal) behaviour of
 the API can be changed by using the similar
 L<SSL_CTX_set_mode(3)> and SSL_set_mode() functions.

 During a handshake, the option settings of the SSL object are used. When
 a new SSL object is created from a context using SSL_new(), the current
 option setting is copied. Changes to B<ctx> do not affect already created
 SSL objects. SSL_clear() does not affect the settings.

 The following B<bug workaround> options are available:

 =over 4

 =item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG

 ...

 =item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER

 ...

 =item SSL_OP_SAFARI_ECDHE_ECDSA_BUG

 Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X.
 OS X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.

 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG

 ...

 =item SSL_OP_TLS_D5_BUG

 ...

 =item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS

 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
 vulnerability affecting CBC ciphers, which cannot be handled by some
 broken SSL implementations.  This option has no effect for connections
 using other ciphers.

 =item SSL_OP_TLSEXT_PADDING

 Adds a padding extension to ensure the ClientHello size is never between
 256 and 511 bytes in length. This is needed as a workaround for some
 implementations.

 =item SSL_OP_ALL

 All of the above bug workarounds.

 =back

 It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
 options if compatibility with somewhat broken implementations is
 desired.

 The following B<modifying> options are available:

 =over 4

 =item SSL_OP_TLS_ROLLBACK_BUG

 Disable version rollback attack detection.

 During the client key exchange, the client must send the same information
 about acceptable SSL/TLS protocol levels as during the first hello. Some
 clients violate this rule by adapting to the server's answer. (Example:
 the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
 only understands up to SSLv3. In this case the client must still use the
 same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
 to the server's answer and violate the version rollback protection.)

 =item SSL_OP_SINGLE_DH_USE

 Always create a new key when using temporary/ephemeral DH parameters
 (see L<SSL_CTX_set_tmp_dh_callback(3)>).
 This option must be used to prevent small subgroup attacks, when
 the DH parameters were not generated using "strong" primes
 (e.g. when using DSA-parameters, see L<dhparam(1)>).
 If "strong" primes were used, it is not strictly necessary to generate
 a new DH key during each handshake but it is also recommended.
 B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
 temporary/ephemeral DH parameters are used.

 =item SSL_OP_EPHEMERAL_RSA

 This option is no longer implemented and is treated as no op.

 =item SSL_OP_CIPHER_SERVER_PREFERENCE

 When choosing a cipher, use the server's preferences instead of the client
 preferences. When not set, the SSL server will always follow the clients
 preferences. When set, the SSL/TLS server will choose following its
 own preferences.

 =item SSL_OP_PKCS1_CHECK_1

 ...

 =item SSL_OP_PKCS1_CHECK_2

 ...


 =item SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1,
 SSL_OP_NO_TLSv1_2, SSL_OP_NO_DTLSv1, SSL_OP_NO_DTLSv1_2

 These options turn off the SSLv3, TLSv1, TLSv1.1 or TLSv1.2 protocol
 versions with TLS or the DTLSv1, DTLSv1.2 versions with DTLS,
 respectively.
 As of OpenSSL 1.1.0, these options are deprecated, use
 L<SSL_CTX_set_min_proto_version(3)> and
 L<SSL_CTX_set_max_proto_version(3)> instead.

 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION

 When performing renegotiation as a server, always start a new session
 (i.e., session resumption requests are only accepted in the initial
 handshake). This option is not needed for clients.

 =item SSL_OP_NO_TICKET

 Normally clients and servers will, where possible, transparently make use
 of RFC4507bis tickets for stateless session resumption.

 If this option is set this functionality is disabled and tickets will
 not be used by clients or servers.

 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION

 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
 servers. See the B<SECURE RENEGOTIATION> section for more details.

 =item SSL_OP_LEGACY_SERVER_CONNECT

 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
 B<only>: this option is currently set by default. See the
 B<SECURE RENEGOTIATION> section for more details.

 =item SSL_OP_NO_ENCRYPT_THEN_MAC

 Normally clients and servers will transparently attempt to negotiate the
 RFC7366 Encrypt-then-MAC option on TLS and DTLS connection.

 If this option is set, Encrypt-then-MAC is disabled. Clients will not
 propose, and servers will not accept the extension.

 =back

 =head1 SECURE RENEGOTIATION

 OpenSSL always attempts to use secure renegotiation as
 described in RFC5746. This counters the prefix attack described in
 CVE-2009-3555 and elsewhere.

 This attack has far reaching consequences which application writers should be
 aware of. In the description below an implementation supporting secure
 renegotiation is referred to as I<patched>. A server not supporting secure
 renegotiation is referred to as I<unpatched>.

 The following sections describe the operations permitted by OpenSSL's secure
 renegotiation implementation.

 =head2 Patched client and server

 Connections and renegotiation are always permitted by OpenSSL implementations.

 =head2 Unpatched client and patched OpenSSL server

 The initial connection succeeds but client renegotiation is denied by the
 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
 B<handshake_failure> alert in SSL v3.0.

 If the patched OpenSSL server attempts to renegotiate a fatal
 B<handshake_failure> alert is sent. This is because the server code may be
 unaware of the unpatched nature of the client.

 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
 renegotiation B<always> succeeds.

 =head2 Patched OpenSSL client and unpatched server.

 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
 and renegotiation between patched OpenSSL clients and unpatched servers
 succeeds. If neither option is set then initial connections to unpatched
 servers will fail.

 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
 though it has security implications: otherwise it would be impossible to
 connect to unpatched servers (i.e. all of them initially) and this is clearly
 not acceptable. Renegotiation is permitted because this does not add any
 additional security issues: during an attack clients do not see any
 renegotiations anyway.

 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
 B<not> be set by default in a future version of OpenSSL.

 OpenSSL client applications wishing to ensure they can connect to unpatched
 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>

 OpenSSL client applications that want to ensure they can B<not> connect to
 unpatched servers (and thus avoid any security issues) should always B<clear>
 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
 SSL_clear_options().

 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
 renegotiation between OpenSSL clients and unpatched servers B<only>, while
 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
 and renegotiation between OpenSSL and unpatched clients or servers.

 =head1 RETURN VALUES

 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
 after adding B<options>.

 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
 after clearing B<options>.

 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.

 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
 secure renegotiation and 0 if it does not.

 =head1 SEE ALSO

 L<ssl(3)>, L<SSL_new(3)>, L<SSL_clear(3)>,
 L<SSL_CTX_set_tmp_dh_callback(3)>,
 L<SSL_CTX_set_min_proto_version(3)>,
 L<dhparam(1)>

 =head1 HISTORY

 The attempt to always try to use secure renegotiation was added in
 Openssl 0.9.8m.

 =head1 COPYRIGHT

 Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.

 Licensed under the OpenSSL license (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_CTX_set_options, SSL_set_options, SSL_CTX_clear_options,
	SSL_clear_options, SSL_CTX_get_options, SSL_get_options,
	SSL_get_secure_renegotiation_support - manipulate SSL options

	=head1 SYNOPSIS

	#include <openssl/ssl.h>

	long SSL_CTX_set_options(SSL_CTX *ctx, long options);
	long SSL_set_options(SSL *ssl, long options);

	long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
	long SSL_clear_options(SSL *ssl, long options);

	long SSL_CTX_get_options(SSL_CTX *ctx);
	long SSL_get_options(SSL *ssl);

	long SSL_get_secure_renegotiation_support(SSL *ssl);

	=head1 DESCRIPTION

	SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>.
	Options already set before are not cleared!

	SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>.
	Options already set before are not cleared!

	SSL_CTX_clear_options() clears the options set via bitmask in B<options>
	to B<ctx>.

	SSL_clear_options() clears the options set via bitmask in B<options> to B<ssl>.

	SSL_CTX_get_options() returns the options set for B<ctx>.

	SSL_get_options() returns the options set for B<ssl>.

	SSL_get_secure_renegotiation_support() indicates whether the peer supports
	secure renegotiation.
	Note, this is implemented via a macro.

	=head1 NOTES

	The behaviour of the SSL library can be changed by setting several options.
	The options are coded as bitmasks and can be combined by a bitwise B<or>
	operation (\|).

	SSL_CTX_set_options() and SSL_set_options() affect the (external)
	protocol behaviour of the SSL library. The (internal) behaviour of
	the API can be changed by using the similar
	L<SSL_CTX_set_mode(3)> and SSL_set_mode() functions.

	During a handshake, the option settings of the SSL object are used. When
	a new SSL object is created from a context using SSL_new(), the current
	option setting is copied. Changes to B<ctx> do not affect already created
	SSL objects. SSL_clear() does not affect the settings.

	The following B<bug workaround> options are available:

	=over 4

	=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG

	...

	=item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER

	...

	=item SSL_OP_SAFARI_ECDHE_ECDSA_BUG

	Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X.
	OS X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.

	=item SSL_OP_SSLEAY_080_CLIENT_DH_BUG

	...

	=item SSL_OP_TLS_D5_BUG

	...

	=item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS

	Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
	vulnerability affecting CBC ciphers, which cannot be handled by some
	broken SSL implementations. This option has no effect for connections
	using other ciphers.

	=item SSL_OP_TLSEXT_PADDING

	Adds a padding extension to ensure the ClientHello size is never between
	256 and 511 bytes in length. This is needed as a workaround for some
	implementations.

	=item SSL_OP_ALL

	All of the above bug workarounds.

	=back

	It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
	options if compatibility with somewhat broken implementations is
	desired.

	The following B<modifying> options are available:

	=over 4

	=item SSL_OP_TLS_ROLLBACK_BUG

	Disable version rollback attack detection.

	During the client key exchange, the client must send the same information
	about acceptable SSL/TLS protocol levels as during the first hello. Some
	clients violate this rule by adapting to the server's answer. (Example:
	the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
	only understands up to SSLv3. In this case the client must still use the
	same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
	to the server's answer and violate the version rollback protection.)

	=item SSL_OP_SINGLE_DH_USE

	Always create a new key when using temporary/ephemeral DH parameters
	(see L<SSL_CTX_set_tmp_dh_callback(3)>).
	This option must be used to prevent small subgroup attacks, when
	the DH parameters were not generated using "strong" primes
	(e.g. when using DSA-parameters, see L<dhparam(1)>).
	If "strong" primes were used, it is not strictly necessary to generate
	a new DH key during each handshake but it is also recommended.
	B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
	temporary/ephemeral DH parameters are used.

	=item SSL_OP_EPHEMERAL_RSA

	This option is no longer implemented and is treated as no op.

	=item SSL_OP_CIPHER_SERVER_PREFERENCE

	When choosing a cipher, use the server's preferences instead of the client
	preferences. When not set, the SSL server will always follow the clients
	preferences. When set, the SSL/TLS server will choose following its
	own preferences.

	=item SSL_OP_PKCS1_CHECK_1

	...

	=item SSL_OP_PKCS1_CHECK_2

	...


	=item SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1,
	SSL_OP_NO_TLSv1_2, SSL_OP_NO_DTLSv1, SSL_OP_NO_DTLSv1_2

	These options turn off the SSLv3, TLSv1, TLSv1.1 or TLSv1.2 protocol
	versions with TLS or the DTLSv1, DTLSv1.2 versions with DTLS,
	respectively.
	As of OpenSSL 1.1.0, these options are deprecated, use
	L<SSL_CTX_set_min_proto_version(3)> and
	L<SSL_CTX_set_max_proto_version(3)> instead.

	=item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION

	When performing renegotiation as a server, always start a new session
	(i.e., session resumption requests are only accepted in the initial
	handshake). This option is not needed for clients.

	=item SSL_OP_NO_TICKET

	Normally clients and servers will, where possible, transparently make use
	of RFC4507bis tickets for stateless session resumption.

	If this option is set this functionality is disabled and tickets will
	not be used by clients or servers.

	=item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION

	Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
	servers. See the B<SECURE RENEGOTIATION> section for more details.

	=item SSL_OP_LEGACY_SERVER_CONNECT

	Allow legacy insecure renegotiation between OpenSSL and unpatched servers
	B<only>: this option is currently set by default. See the
	B<SECURE RENEGOTIATION> section for more details.

	=item SSL_OP_NO_ENCRYPT_THEN_MAC

	Normally clients and servers will transparently attempt to negotiate the
	RFC7366 Encrypt-then-MAC option on TLS and DTLS connection.

	If this option is set, Encrypt-then-MAC is disabled. Clients will not
	propose, and servers will not accept the extension.

	=back

	=head1 SECURE RENEGOTIATION

	OpenSSL always attempts to use secure renegotiation as
	described in RFC5746. This counters the prefix attack described in
	CVE-2009-3555 and elsewhere.

	This attack has far reaching consequences which application writers should be
	aware of. In the description below an implementation supporting secure
	renegotiation is referred to as I<patched>. A server not supporting secure
	renegotiation is referred to as I<unpatched>.

	The following sections describe the operations permitted by OpenSSL's secure
	renegotiation implementation.

	=head2 Patched client and server

	Connections and renegotiation are always permitted by OpenSSL implementations.

	=head2 Unpatched client and patched OpenSSL server

	The initial connection succeeds but client renegotiation is denied by the
	server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
	B<handshake_failure> alert in SSL v3.0.

	If the patched OpenSSL server attempts to renegotiate a fatal
	B<handshake_failure> alert is sent. This is because the server code may be
	unaware of the unpatched nature of the client.

	If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
	renegotiation B<always> succeeds.

	=head2 Patched OpenSSL client and unpatched server.

	If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
	B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
	and renegotiation between patched OpenSSL clients and unpatched servers
	succeeds. If neither option is set then initial connections to unpatched
	servers will fail.

	The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
	though it has security implications: otherwise it would be impossible to
	connect to unpatched servers (i.e. all of them initially) and this is clearly
	not acceptable. Renegotiation is permitted because this does not add any
	additional security issues: during an attack clients do not see any
	renegotiations anyway.

	As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
	B<not> be set by default in a future version of OpenSSL.

	OpenSSL client applications wishing to ensure they can connect to unpatched
	servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>

	OpenSSL client applications that want to ensure they can B<not> connect to
	unpatched servers (and thus avoid any security issues) should always B<clear>
	B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
	SSL_clear_options().

	The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
	B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
	B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
	renegotiation between OpenSSL clients and unpatched servers B<only>, while
	B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
	and renegotiation between OpenSSL and unpatched clients or servers.

	=head1 RETURN VALUES

	SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
	after adding B<options>.

	SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
	after clearing B<options>.

	SSL_CTX_get_options() and SSL_get_options() return the current bitmask.

	SSL_get_secure_renegotiation_support() returns 1 is the peer supports
	secure renegotiation and 0 if it does not.

	=head1 SEE ALSO

	L<ssl(3)>, L<SSL_new(3)>, L<SSL_clear(3)>,
	L<SSL_CTX_set_tmp_dh_callback(3)>,
	L<SSL_CTX_set_min_proto_version(3)>,
	L<dhparam(1)>

	=head1 HISTORY

	The attempt to always try to use secure renegotiation was added in
	Openssl 0.9.8m.

	=head1 COPYRIGHT

	Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.

	Licensed under the OpenSSL license (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