update documentation to reflect new renegotiation options

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

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

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