Allow renegotiation if SSL_OP_LEGACY_SERVER_CONNECT is set as well as

[openssl.git] / doc / ssl / SSL_CTX_set_options.pod

diff --git a/doc/ssl/SSL_CTX_set_options.pod b/doc/ssl/SSL_CTX_set_options.pod
index c10055c6e7aba574e83fe5d0b600654bb88d5dc1..1abda2898e6a2c4a6f73d215b1115562d6110ea2 100644 (file)
--- a/doc/ssl/SSL_CTX_set_options.pod
+++ b/doc/ssl/SSL_CTX_set_options.pod
@@ -2,7 +2,7 @@
 
 =head1 NAME
 
 
 =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
 
 
 =head1 SYNOPSIS
 


@@ -11,31 +11,46 @@ SSL_CTX_set_options, SSL_set_options, SSL_CTX_get_options, SSL_get_options - man
  long SSL_CTX_set_options(SSL_CTX *ctx, long options);
  long SSL_set_options(SSL *ssl, long options);
 
  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_CTX_get_options(SSL_CTX *ctx);
  long SSL_get_options(SSL *ssl);
 

+ long SSL_get_secure_renegotiation_support(SSL *ssl);
+

 =head1 DESCRIPTION
 
 =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_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_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>
 =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.
+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
 
 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
 
 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


@@ -86,7 +101,7 @@ doing a re-connect, always takes the first cipher in the cipher list.
 
 =item SSL_OP_MSIE_SSLV2_RSA_PADDING
 
 
 =item SSL_OP_MSIE_SSLV2_RSA_PADDING
 

-...
+As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.

 
 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
 
 
 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
 


@@ -100,14 +115,22 @@ doing a re-connect, always takes the first cipher in the cipher list.
 
 ...
 
 
 ...
 

+=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_ALL
 
 All of the above bug workarounds.
 
 =back
 
 =item SSL_OP_ALL
 
 All of the above bug workarounds.
 
 =back
 

-It is safe and recommended to use B<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:
 
 
 The following B<modifying> options are available:
 


@@ -155,7 +178,7 @@ 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
 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_PKCS1_CHECK_1
 


@@ -168,7 +191,7 @@ will send his list of preferences to the client and the client chooses.
 =item SSL_OP_NETSCAPE_CA_DN_BUG
 
 If we accept a netscape connection, demand a client cert, have a
 =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
+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
 browser has a cert, it will crash/hang.  Works for 3.x and 4.xbeta 
 
 =item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG


@@ -191,17 +214,105 @@ Do not use the TLSv1 protocol.
 
 When performing renegotiation as a server, always start a new session
 (i.e., session resumption requests are only accepted in the initial
 
 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.
+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, SSL_OP_LEGACY_SERVER_CONNECT
+
+See the B<SECURE RENEGOTIATION> section for a discussion of the purpose of
+these options.

 
 =back
 
 
 =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 suceeds 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> is set then initial connections
+and renegotiation between patched OpenSSL clients and unpatched servers
+succeeds.
+
+This option 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().
+
+As in the previous case if the option
+B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then renegotiation
+B<always> succeeds.
+

 =head1 RETURN VALUES
 
 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
 after adding B<options>.
 
 =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_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 SEE ALSO
 
 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,


@@ -219,4 +330,16 @@ 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.
 
 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
 =cut