Re: [TLS] Negotiate only symmetric cipher via cipher suites (was: Ala Carte Cipher suites - was: DSA should die)

Dmitry Belyavsky <beldmit@gmail.com> Mon, 13 April 2015 18:57 UTC

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References: <CAK9dnSyKf7AY11h1i1h+SudRc-NmTZE5wC682YKhNsxnfV5ShQ@mail.gmail.com> <201504131200.00384.davemgarrett@gmail.com> <874mokug5y.fsf@alice.fifthhorseman.net> <201504131325.20590.davemgarrett@gmail.com> <871tjoue8v.fsf@alice.fifthhorseman.net> <D1517606.23FD5%uri@ll.mit.edu> <87vbgzubj6.fsf@alice.fifthhorseman.net> <20150413185505.GA1016@LK-Perkele-VII>
Date: Mon, 13 Apr 2015 21:57:04 +0300
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From: Dmitry Belyavsky <beldmit@gmail.com>
To: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
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Subject: Re: [TLS] Negotiate only symmetric cipher via cipher suites (was: Ala Carte Cipher suites - was: DSA should die)
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Hello Ilari,

You missed GOST key exchange.

Thank you!

On Mon, Apr 13, 2015 at 9:55 PM, Ilari Liusvaara <
ilari.liusvaara@elisanet.fi> wrote:

> On Mon, Apr 13, 2015 at 02:29:49PM -0400, Daniel Kahn Gillmor wrote:
> > On Mon 2015-04-13 13:35:42 -0400, Blumenthal, Uri - 0553 - MITLL wrote:
> > > On 4/13/15, 13:31 , "Daniel Kahn Gillmor" <dkg@fifthhorseman.net>
> wrote:
> > >
> > >>On Mon 2015-04-13 13:25:20 -0400, Dave Garrett wrote:
> > >>>> So if we have to have non-(EC)DHE PSK, what would it mean if a TLS
> peer
> > >>>> were to try to negotiate:
> > >>>>
> > >>>>   key agreement: PSK
> > >>>>  authentication: RSA-PSS
> > >>>>
> > >>>> Do we just say "don't do that"?
> > >>>
> > >>> SGTM
> > >>
> > >>……...
> > >>Once the full cartesian explosion is available by multidimensional
> > >>enumeration, we have to mark out which corners of the space are
> actually
> > >>bad ideas, and we have to make sure our implementations don't stumble
> > >>into those corners by accident.
> > >>
> > >>This isn't impossible to do, but it seems ripe for subtle
> implementation
> > >>bugs.
> > >
> > > Cryptographically sound algorithms and protocols should be immune to
> this
> > > concern. And we should accept only cryptographically sound algorithms &
> > > protocols. :-)
> >
> > What do you think an implementation should do when a peer tries to
> > negotiate the combination above?  Require an RSA-PSS signature from the
> > server over some material derived in part from the PSK key agreement
> > mechanism?
>
> To me it seems like that combo is quite insecure, unless one handles it as
> a special case (in which case it is just equivalent to PSK in security,
> just wastes time with a certificate).
>
>
> As list, the key exchange methods TLS v1.2 actually supports (after merging
> some non-significant distinctions) are:
> - RSA [going away]
> - RSA_EXPORT [you have deimplemented this already, right?]
> - DH_CERT [going away]
> - DHE_CERT [supported]
> - DHE_ANON [???]
> - KRB5 [going away]
> - PSK [???]
> - DHE_PSK [???]
> - RSA_PSK [going away]
> - SRP [???]
> - SRP_CERT [???]
>
>
>
> -Ilari
>
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>



-- 
SY, Dmitry Belyavsky