[gnutls-devel] [RFC] Relaxing cipher suite (priority) string requirements

Nikos Mavrogiannopoulos nmav at gnutls.org
Tue Jan 29 09:29:50 CET 2013

On 01/28/2013 07:54 AM, Jouko Orava wrote:

>> It could be two different modes. One that you specify explicitly
>> ciphersuites, and the other that is like now (level+ciphers,macs etc.).
>> Does this make sense?
> Absolutely, and that's also the reason I haven't yet tested the patches I
> proposed earlier (making '+' optional, for example).
> Here's the logic rules I've been considering.
> I'm not entirely happy with it, and I think it needs further work.
> It is quite possibly too complicated (for users).
> (I do believe the implementation would be straightforward, though.)
> 	"!" <ciphersuite>
> 	"!" <protocol>
> 	"!" <certificate>
> 	"!" <compression>
> 	"!" <signature>
> 	"!" <cipher>
> 	"!" <mac>
> 	"!" <key exchange>
> 		Completely disallow (ban).
> 		Applies as if these were listed last in the string.
> 	"!" <level>
> 		Ban all cipher suites in <level>
> 		from the current priority set.
> 		(Other features of <level> are ignored.)

What is the purpose of being able to remove ciphersuites from a level?

> Instead of "-ALL" suffixes, catch-alls could use an asterisk "*".
> For example, any TLSv1 protocol could be "TLSv1.*".

That is more intuitive and could be added to the old format as well, in
a backwards compatible way.

> "NONE" should include "no compression". Compression can be required
> by explicitly banning or removing "no compression".

Why is that? None should be really none, so that you can specify exactly
what you need. That's how it is used now.

> To distinguish between the existing parsing, this format would
> require a start marker, for example "@" or "New".

I'd propose the new string to be simpler:
> 	x <ciphersuite>
> 	x <protocol>
> 	x <certificate>
> 	x <compression>
> 	x <signature>
>       % <cmd>
x = + | " "

That is you'll choose the new format to specify ciphersuites, and use
the old format if you want to specify individual algorithms/levels.

I wouldn't like to have more than a way to do the same thing.


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