=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
+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
=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_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 logical B<or>
+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)|SSL_CTX_set_mode(3)> and SSL_set_mode() functions.
+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
=over 4
-=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.
-
-=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.
-
-=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.
-
=item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
...
...
-=item SSL_OP_MSIE_SSLV2_RSA_PADDING
+=item SSL_OP_SAFARI_ECDHE_ECDSA_BUG
-As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
+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
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.
=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)|SSL_CTX_set_tmp_dh_callback(3)>).
+(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)|dhparam(1)>).
+(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
=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
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 SSLv3/TLSv1 server will choose following its
-own preferences. Because of the different protocol, for SSLv2 the server
-will send its list of preferences to the client and the client chooses.
+preferences. When set, the SSL/TLS server will choose following its
+own preferences.
=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-signed CA which does not have its 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 SSLv2 protocol.
-
-=item SSL_OP_NO_SSLv3
-Do not use the SSLv3 protocol.
+=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
-=item SSL_OP_NO_TLSv1
-
-Do not use the TLSv1 protocol.
+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
=item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
-See the B<SECURE RENEGOTIATION> section for a discussion of the purpose of
-this option
+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 0.9.8m and later always attempts to use secure renegotiation as
-described in draft-ietf-tls-renegotiation (FIXME: replace by RFC). This
-counters a prefix attack described in the draft and elsewhere (FIXME: need full
-reference).
+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>.
-If an unpatched client attempts to connect to a patched OpenSSL server then
-the attempt will succeed but renegotiation is not permitted. As required
-by the standard a B<no_renegotiation> alert is sent back to the client if
-the TLS v1.0 protocol is used. If SSLv3.0 is used then renegotiation results
-in a fatal B<handshake_failed> alert.
+The following sections describe the operations permitted by OpenSSL's secure
+renegotiation implementation.
-If a patched OpenSSL client attempts to connect to an unpatched server
-then the connection will fail because it is not possible to determine
-whether an attack is taking place.
+=head2 Patched client and server
-If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then the
-above restrictions are relaxed. Renegotiation is permissible and initial
-connections to unpatched servers will succeed.
+Connections and renegotiation are always permitted by OpenSSL implementations.
-This option should be used with caution because it leaves both clients and
-servers vulnerable. However unpatched servers and clients are likely to be
-around for some time and refusing to connect to unpatched servers or denying
-renegotion altogether may be unacceptable. So applications may be forced to
-tolerate unsafe renegotiation for the immediate future.
+=head2 Unpatched client and patched OpenSSL server
-The function SSL_get_secure_renegotiation_support() indicates whether the peer
-supports secure renegotiation.
+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.
-The deprecated SSLv2 protocol does not support secure renegotiation at all.
+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
=head1 SEE ALSO
-L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
-L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
-L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
-L<dhparam(1)|dhparam(1)>
+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
-B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
-B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
-OpenSSL 0.9.7.
-
-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.
+The attempt to always try to use secure renegotiation was added in
+Openssl 0.9.8m.
-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).
+=head1 COPYRIGHT
-SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
-0.9.8m.
+Copyright 2001-2016 The OpenSSL Project Authors. All Rights Reserved.
-B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> was first added in OpenSSL
-0.9.8m.
+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
projects / openssl.git / blobdiff