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| -rw-r--r-- | doc/gnutls.texi | 50 |
1 files changed, 28 insertions, 22 deletions
diff --git a/doc/gnutls.texi b/doc/gnutls.texi index 3dc3b1f177..312bc23a59 100644 --- a/doc/gnutls.texi +++ b/doc/gnutls.texi @@ -1262,32 +1262,38 @@ initial negotiation. When the extension is used, the attack is detected and the session can be terminated. The extension is specified in @xcite{RFC5746}. -GnuTLS supports the safe renegotiation extension. By default, GnuTLS -clients will attempt to negotiate the safe renegotiation extension -when talking to servers. Also by default, GnuTLS servers will accept -the extension when presented by clients. However, by default GnuTLS -client and servers will not refuse renegotiation attempts when the -extension has not been negotiated, as this would break backwards -compatibility and cause too much operational problems. We will likely -reconsider these defaults in the future. - -To modify the default behaviour, we have introduced four new priority +GnuTLS supports the safe renegotiation extension. The default +behavior is as follows. Clients will attempt to negotiate the safe +renegotiation extension when talking to servers. Servers will accept +the extension when presented by clients. Clients and servers will +permit an initial handshake to complete even when the other side does +not support the safe renegotiation extension. Clients and servers +will refuse renegotiation attempts when the extension has not been +negotiated. + +Note that permitting clients to connect to servers even when the safe +renegotiation extension is not negotiated open up for some attacks. +Changing this default behaviour would prevent interoperability against +the majority of deployed servers out there. We will reconsider this +default behaviour in the future when more servers have been upgraded. +Note that it is easy to configure clients to always require the safe +renegotiation extension from servers (see below on the +%SAFE_RENEGOTIATION priority string). + +To modify the default behaviour, we have introduced some new priority strings. The priority strings can be used by applications (@pxref{gnutls_priority_set}) and end users (e.g., @code{--priority} parameter to @code{gnutls-cli} and @code{gnutls-serv}). -The @code{%UNSAFE_RENEGOTIATION} priority string requests what is -today the default behaviour, i.e., that handshakes without the safe -renegotiation extension is permitted. To make more use of the -extension, you may provide the @code{%SAFE_RENEGOTIATION} priority -string. In this mode, clients will require that the server supports -the extension for the initial handshake, and servers will require that -the client supports the extension for renegotiated handshakes. If you -want to make a server refuse even initial handshakes without the safe -renegotiation extension, use the @code{%INITIAL_SAFE_RENEGOTIATION} -priority string. It is possible to disable use of the extension -completely by using the @code{%DISABLE_SAFE_RENEGOTIATION} priority -string however this is recommended against except for debugging. +The @code{%UNSAFE_RENEGOTIATION} priority string permits +(re-)handshakes even when the safe renegotiation extension was not +negotiated. The @code{%SAFE_RENEGOTIATION} priority string makes +client and servers require the extension for every handshake. + +It is possible to disable use of the extension completely, in both +clients and servers, by using the @code{%DISABLE_SAFE_RENEGOTIATION} +priority string however we strongly recommend you to only do this for +debugging and test purposes. For applications we have introduced a new API related to safe renegotiation. The @ref{gnutls_safe_renegotiation_status} function is |