On Tue, Sep 20, 2016 at 2:14 PM Hubert Kario <hka...@redhat.com> wrote:
> On Tuesday, 20 September 2016 15:56:01 CEST David Benjamin wrote: > > On Tue, Sep 20, 2016 at 11:33 AM Ilari Liusvaara < > ilariliusva...@welho.com> > > > > wrote: > > > On Tue, Sep 20, 2016 at 03:07:51PM +0000, David Benjamin wrote: > > > > Hi folks, > > > > > > > > I've just uploaded this PR to slightly tweak SignatureScheme > numbering: > > > > https://github.com/tlswg/tls13-spec/pull/641 > > > > > > > > In principle, we should only have needed to burn values starting with > > > > > > known > > > > > > > HashAlgorithms, but TLS 1.2 said: > > > > signature > > > > > > > > This field indicates the signature algorithm that may be used. > > > > The values indicate anonymous signatures, RSASSA-PKCS1-v1_5 > > > > [PKCS1] and DSA [DSS], and ECDSA [ECDSA], respectively. The > > > > "anonymous" value is meaningless in this context but used in > > > > Section 7.4.3. It MUST NOT appear in this extension. > > > > > > > > We'd started RSA-PSS along the train to get shipped in Chrome to get > > > > > > early > > > > > > > warning on any interoperability issues. We ran into an implementation > > > > > > which > > > > > > > enforced this MUST NOT. It's a MUST NOT in 1.2, so it seems prudent > to > > > > allocate around it and avoid ending in known SignatureAlgorithms. > Thus, > > > > rather than only burning {0x00-0x06, *}, we also burn {*, 0x00-0x03}. > > > > > > This > > > > > > > has the added benefit that TLS 1.2 dissector tools don't get > confused. > > > > > > Heck, I think one could put the RSA-PSS ones as 0404, 0504 and 0604, > > > as those do have the indicated "prehashes". > > > > > > And one could probably also stick Ed25519/Ed448 in 00xx, as those have > > > no prehash, which is exactly what "hash #0" is about. > > > > > > (Of course, this all is pretty pointless bikeshedding). > > > > The ecdsa_p256_sha256 business means that the old scheme isn't quite > > accurate. And if we are to drop the old scheme, it was intentional on my > > part that RSA-PSS did not look like it, even though it still fit. I think > > that paid off. No one's going to implement Ed25519 for a while, so > RSA-PSS > > is our smoke test that this SignatureScheme idea is sane. (Both for > interop > > and for making sure removing the hash/sig decomposition in > implementations > > internally is sound.) > > I'll be running test looking for intolerances like this over the Alexa top > 1 > million next month. > (I've already done this, by the way. It's where the numbers in the version negotiation thread came from.) > For now I have a probe that adds values 0x0003, 0x0004, 0x0700, 0x0703 and > 0x0704 at the end of the list of algorithms. > At the front is probably more realistic. There is even a MUST-level requirement in the current TLS 1.3 spec for SHA-1 sigalgs to be at the end, so the new ones can't be (unless you take SHA-1 out, which is, sadly, unrealistic today... an upsetting number of 1.2 servers only sign SHA-1). I was able to find a few instances of an NSS bug ( https://bugzilla.mozilla.org/show_bug.cgi?id=1119983), but nothing else. The offending implementation for this thread was actually a WebRTC stack (DTLS), not an HTTPS server. We hit it via Chrome's Dev channel. But since this intolerance comes from a MUST-level requirement in TLS 1.2, I think it's prudent to renumber. > Would you suggest doing something more with it? > > (I will be looking for key_share extension intolerance as a whole too) > -- > Regards, > Hubert Kario > Senior Quality Engineer, QE BaseOS Security team > Web: www.cz.redhat.com > Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic
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