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-rw-r--r--doc/ssl/SSL_CTX_set_options.pod120
1 files changed, 117 insertions, 3 deletions
diff --git a/doc/ssl/SSL_CTX_set_options.pod b/doc/ssl/SSL_CTX_set_options.pod
index eaed19080975..06025d13fafb 100644
--- a/doc/ssl/SSL_CTX_set_options.pod
+++ b/doc/ssl/SSL_CTX_set_options.pod
@@ -2,7 +2,7 @@
=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
@@ -11,26 +11,41 @@ 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_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.
+operation (|).
SSL_CTX_set_options() and SSL_set_options() affect the (external)
protocol behaviour of the SSL library. The (internal) behaviour of
@@ -199,7 +214,7 @@ 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
-handshake). This option is not needed for clients.
+handshake). This option is not needed for clients.
=item SSL_OP_NO_TICKET
@@ -210,15 +225,107 @@ is explicitly set when OpenSSL is compiled.
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 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> 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)>,
@@ -241,4 +348,11 @@ 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