Re: [TLS] (crypto agility may benefit from private extensions) Re: Additional changes for draft-ietf-tls-iana-registry-updates

Eric Rescorla <> Tue, 20 March 2018 14:55 UTC

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From: Eric Rescorla <>
Date: Tue, 20 Mar 2018 14:54:24 +0000
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To: Rene Struik <>
Cc: Sean Turner <>, "<>" <>
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Subject: Re: [TLS] (crypto agility may benefit from private extensions) Re: Additional changes for draft-ietf-tls-iana-registry-updates
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On Tue, Mar 20, 2018 at 2:51 PM, Rene Struik <>; wrote:

> Hi Sean:
> Quick question: does "closing the registry" not contradict catering
> towards crypto agility? What happens if, say, one wishes to add another
> signature scheme, besides Ed25519, to the mix. If there is no private
> field, does this mean that, e.g., Schnorr+BSI Brainpool256r1 is now ruled
> out?

No. Private just means "we're not going to allocate these code points, so
you should use them without coordination".

The key point here is that this is a big space and so we're instead going
to make it easy for people to reserve code points by writing a stable spec,
that need not be an IETF standard, and that's what they should do.


> My more serious concern is, however, that if the Private Use case is
> "verboten", there is no chance for people to signal private extensions
> (since IETF will just have killed this off).
> I do not think it is prudent to have a slow process in place (IETF
> standardization) to effectuate crypto agility, if private use can already
> do this without waiting for 3-year public discussions and heated debate (if
> a weakness is discovered, dark forces will exploit this right away and
> won't wait for IETF to catch up to exploit an issue).
> As case in point, suppose US Gov't wants to roll its own "Suite A" scheme,
> or if one wants to use TLS with something tailored towards the sensor world
> (which operates in quite a hostile environment for implementation
> security), how is one going to do this in context of TLS if the signaling
> required has just been removed?
> NOTE: this is not an invite for endless discussions on the legitimacy of
> whoever may wish a private extensions (it is private after all), it does
> question though the wisdom of removing the option for using this. If Zulu
> hour arrives, one should have tools to act...
> Best regards, Rene
> On 3/16/2018 10:01 AM, Sean Turner wrote:
> > During Adam Roach’s AD review of draft-ietf-tls-tls13, he noted
> something about the HashAlgorithm and that made me go look at what was said
> in draft-ietf-tls-iana-registry-updates.  Turns out that 4492bis assigned
> some values draft-ietf-tls-iana-registry-updates was marking as
> reserved.  I have fixed that up in:
> >
> >
> > One further point brought out in discussions with Adam was that if we’re
> really closing the HashAlgorithm and SignatureAlgorithms registry we need
> to also mark 224-255 as deprecated.  Currently these are marked as Reserved
> for Private Use.  So the question is should we mark 224-255 as deprecated
> in these two registries?
> >
> > spt
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