On Tue, Jul 10, 2018 at 6:38 AM, Hubert Kario <hka...@redhat.com> wrote:
> On Tuesday, 10 July 2018 06:17:56 CEST Viktor Dukhovni wrote: > > On Tue, Jul 10, 2018 at 08:56:14AM +1000, Martin Thomson wrote: > > > Is there any reason why we wouldn't also consider deprecating cipher > > > suites we don't like? For instance, RFC 5246 mandates the > > > implementation of TLS_RSA_WITH_AES_128_CBC_SHA, which we can probably > > > agree isn't ideal for several reasons. > > > > Is the objection primarily to AES-128-CBC or to RSA key exchange? > > With EtM there's AFAIK/IMHO not much wrong with AES-128-CBC, it > > outperforms AES-256-CBC, and the various CBC issues are resolved > > via EtM. > > > > > The ECDHE suites with AES-GCM > > > are widely available, perhaps widely enough that we might consider a > > > stronger move and update 5246 to modern suites. > > > > More generally, as noted in RFC7435, you get more security by raising > > the ceiling than by raising the floor. Breaking the ability to > > communicate with legacy systems may feel satisfying, but does not > > generally improve the security of the up-to-date systems, barring > > downgrade issues in the protocol. > > The github version of the document points out that the security of TLS 1.2 > downgrade protection to TLS 1.1 or TLS 1.0 depends on SHA-1. > Well, yes and no. If you allow static RSA, then yes. If you require (EC)DHE, then the anti-downgrade measures in the TLS 1.3 random values are intended to protect against downgrade even if SHA-1 is compromised (because the randoms are signed). -Ekr > that is the downgrade issue in the protocol > > https://github.com/sftcd/tls-oldversions-diediedie/blob/ > bd6bdc37ec258094f1e1010fba19e8763f2beaee/draft-moriarty-tls-oldversions- > diediedie.txt#L142-L145 > -- > Regards, > Hubert Kario > Senior Quality Engineer, QE BaseOS Security team > Web: www.cz.redhat.com > Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls > >
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