Re: HTTP2 allowed ciphers

On 29/04/2016 10:33 p.m., Philipp Junghannß wrote:
> I have read the forbidden ciphers for HTTP2 (appendix A) which is quite a
> long list and I think it might be intresting to see what ciphers actually
> ARE allowed, also because whitelisting a small number of ciphers might be
> more efficient than blacklisting everything that's listed there (especially
> concidering the different naming conventions among servers.
> 

The result of that test depends on your library and its age. IIRC you
will find that AEAD, EC, DH or AES GCM based ciphers are almost the only
allowed ones. Those are all fairly recent developments and not available
on OS more than a few years old.

(One would expect that any OS getting updated to software doing h2 is
also capable of getting security library updates. But weirder things
have happened in HTTP.)

The blacklist set is fixed, whereas the whitelist is variable and must
also cope with a group of not-yet-invented ciphers. Figuring out that
variable part on the go can be a lot less efficient than using a static
blacklist and leaving the details to the library.

It is up to you how to implement of course. Just saying blacklist is
actually the easy way. You can also shortcut the list somewhat - notice
that CBC, RC4, etc. are common occurance on the forbidden so just making
your software avoid old cruft will get you a long way towards compliance
and will help with general HTTPS security as well.

Amos

Received on Friday, 29 April 2016 12:18:38 UTC