=head1 NAME
-SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - manipulate SSL engine options
+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
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
+Note: all these functions are implemented using macros.
+
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.
+
=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 logical B<or>
-operation (|). Options can only be added but can never be reset.
+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_modes(3)|SSL_CTX_set_modes(3)> and SSL_set_modes() functions.
+L<SSL_CTX_set_mode(3)|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
=item SSL_OP_MICROSOFT_SESS_ID_BUG
-www.microsoft.com - when talking SSLv2, if session-id reuse is
-performed, the session-id passed back in the server-finished message
-is different from the one decided upon.
+As of OpenSSL 1.0.0 this option has no effect.
=item SSL_OP_NETSCAPE_CHALLENGE_BUG
-Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte
-challenge but then appears to only use 16 bytes when generating the
-encryption keys. Using 16 bytes is ok but it should be ok to use 32.
-According to the SSLv3 spec, one should use 32 bytes for the challenge
-when operating in SSLv2/v3 compatibility mode, but as mentioned above,
-this breaks this server so 16 bytes is the way to go.
+As of OpenSSL 1.0.0 this option has no effect.
=item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
-ssl3.netscape.com:443, first a connection is established with RC4-MD5.
-If it is then resumed, we end up using DES-CBC3-SHA. It should be
-RC4-MD5 according to 7.6.1.3, 'cipher_suite'.
-
-Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug.
-It only really shows up when connecting via SSLv2/v3 then reconnecting
-via SSLv3. The cipher list changes....
-
-NEW INFORMATION. Try connecting with a cipher list of just
-DES-CBC-SHA:RC4-MD5. For some weird reason, each new connection uses
-RC4-MD5, but a re-connect tries to use DES-CBC-SHA. So netscape, when
-doing a re-connect, always takes the first cipher in the cipher list.
+As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect.
=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...
-=item SSL_OP_MSIE_SSLV2_RSA_PADDING
+=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_BLOCK_PADDING_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
=back
-It is safe and recommended to use SSL_OP_ALL to enable the bug workaround
-options.
+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:
(e.g. when using DSA-parameters, see L<dhparam(1)|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.
-SSL_OP_SINGLE_DH_USE should therefore be enabled whenever
+B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
temporary/ephemeral DH parameters are used.
=item SSL_OP_EPHEMERAL_RSA
-Always use ephemeral (temporary) RSA key when doing RSA operations
-(see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
-According to the specifications this is only done, when a RSA key
-can only be used for signature operations (namely under export ciphers
-with restricted RSA keylength). By setting this option, ephemeral
-RSA keys are always used. This option breaks compatibility with the
-SSL/TLS specifications and may lead to interoperability problems with
-clients and should therefore never be used. Ciphers with EDH (ephemeral
-Diffie-Hellman) key exchange should be used instead.
+This option is no longer implemented and is treated as no op.
=item SSL_OP_CIPHER_SERVER_PREFERENCE
preferences. When not set, the SSL server will always follow the clients
preferences. When set, the SSLv3/TLSv1 server will choose following its
own preferences. Because of the different protocol, for SSLv2 the server
-will send his list of preferences to the client and the client chooses.
+will send its list of preferences to the client and the client chooses.
=item SSL_OP_PKCS1_CHECK_1
...
-=item SSL_OP_NETSCAPE_CA_DN_BUG
-If we accept a netscape connection, demand a client cert, have a
-non-self-sighed CA which does not have it's CA in netscape, and the
-browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
-
-=item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
-
-...
=item SSL_OP_NO_SSLv2
Do not use the TLSv1 protocol.
+=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.
+
=back
+=head1 SECURE RENEGOTIATION
+
+OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
+described in RFC5746. This counters the prefix attack described in
+CVE-2009-3555 and elsewhere.
+
+The deprecated and highly broken SSLv2 protocol does not support
+renegotiation at all: its use is B<strongly> discouraged.
+
+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.
+
+B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
+unpatched) will result in the connection hanging if it receives a
+B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
+a B<no_renegotiation> alert as fatal and respond with a fatal
+B<handshake_failure> alert. This is because the OpenSSL API currently has
+no provision to indicate to an application that a renegotiation attempt
+was refused.
+
+=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)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
=head1 HISTORY
-SSL_OP_CIPHER_SERVER_PREFERENCE has been added in OpenSSL 0.9.7.
+B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
+B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
+OpenSSL 0.9.7.
-SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6 and was automatically
-enabled with SSL_OP_ALL. As of 0.9.7 it is no longer included in SSL_OP_ALL
+B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
+enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
and must be explicitly set.
+B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
+Versions up to OpenSSL 0.9.6c do not include the countermeasure that
+can be disabled with this option (in OpenSSL 0.9.6d, it was always
+enabled).
+
+SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
+0.9.8m.
+
+B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
+and the function SSL_get_secure_renegotiation_support() were first added in
+OpenSSL 0.9.8m.
+
=cut
projects / openssl.git / blobdiff