Re: [TLS] Simplifying signature algorithm negotiation

Ilari Liusvaara <ilariliusvaara@welho.com> Thu, 17 March 2016 17:41 UTC

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Date: Thu, 17 Mar 2016 19:34:37 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: David Benjamin <davidben@chromium.org>
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References: <CAF8qwaCpYqs7ELDcRzXveLLjpL+d-CmBczkxPweh6_RVE1aDeA@mail.gmail.com> <201601152007.12464.davemgarrett@gmail.com> <CAF8qwaBPsLz-vuOvXGZgxzMpaKHwtZixu7NXzfFN4V_R6WT8Tg@mail.gmail.com> <CABcZeBNipj4oLU=FrTp3+CqTg5bh5vBnd04DoNt56=8BRjqobw@mail.gmail.com> <CAF8qwaDUbLmvzibuC7aedOR5TP6Fv3rNz6ft_v3bKu=FHatYgg@mail.gmail.com> <CABcZeBMGnma86M24hzQw6zmwftMte2Lr34TGuq2pUF0MTGZMUQ@mail.gmail.com> <CAF8qwaDdi9JNNKUCBsuQmw3AssaiKvMgSs_8bCebfmBRdzCAQw@mail.gmail.com>
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Subject: Re: [TLS] Simplifying signature algorithm negotiation
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On Tue, Mar 15, 2016 at 05:37:20PM +0000, David Benjamin wrote:
> On Mon, Mar 14, 2016 at 8:22 PM Eric Rescorla <ekr@rtfm.com>; wrote:
> 
> 
> I would probably characterize it less as suites vs orthogonality, but as
> wanting to keep divisions in meaningful and universal places and not
> splitting up tightly-coupled decisions. The flexibility from orthogonality
> can be handy, but going too far---as I believe TLS 1.2 did with signature,
> prehash, and curve---complicates everything. Imagine if negotiating
> AES_128_GCM required separately negotiating block cipher AES-128, mode CTR,
> and MAC GHASH.

It isn't even orthogonal, it is coupled, which is way worse and quite
difficult to implement correctly.

I now consider the way TLS 1.3 draft / RFC4492bis draft currently does
EdDSA negotiation a bad idea (what is proposed here is vast improvement).


-Ilari