update documentation to reflect new renegotiation options

1 files changed, 46 insertions, 23 deletions

diff --git a/doc/ssl/SSL_CTX_set_options.pod b/doc/ssl/SSL_CTX_set_options.pod
index 9331e67153..7ffe948112 100644
--- a/doc/ssl/SSL_CTX_set_options.pod
+++ b/doc/ssl/SSL_CTX_set_options.pod
@@ -224,10 +224,10 @@ 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
+=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
-this option
+these options.
 
 =back
 
@@ -235,38 +235,60 @@ this option
 
 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).
+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.
+=head2 Patched client and server
 
-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.
+Connections and renegotiation will always succeed.
 
-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.
+=head2 Unpatched client and patched server
 
-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.
+The initial connection suceeds but client renegotiation is denied 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 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.
+
+=head2 Patched client and unpatched server.
+
+If the option B<SSL_OP_LEGACY_SERVER_CONNECT> is set then initial connections
+to unpatched servers succeed. 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.
+
+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.
+
+Applications that want to ensure they can connect to unpatched servers should
+always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
+
+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 function SSL_get_secure_renegotiation_support() indicates whether the peer
 supports secure renegotiation. 
 
-The deprecated SSLv2 protocol does not support secure renegotiation at all.
+The deprecated and highly broken SSLv2 protocol does not support secure
+renegotiation at all: its use is B<strongly> discouraged.
 
 =head1 RETURN VALUES
 
@@ -306,7 +328,8 @@ enabled).
 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
 0.9.8m.
 
-B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> was 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