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[Ssh] Re: Supporting pure ML-DSA as hostkey and authkey

Simon Josefsson <simon@josefsson.org> Wed, 29 April 2026 18:16 UTC

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From: Simon Josefsson <simon@josefsson.org>
To: Dennis Jackson <ietf=40dennis-jackson.uk@dmarc.ietf.org>
In-Reply-To: <867cbc77-a08c-40d4-b665-75939eab065a@dennis-jackson.uk> (Dennis Jackson's message of "Wed, 29 Apr 2026 18:36:04 +0100")
References: <68bc138c-ccfc-2d97-0f25-64271655c23b@mindrot.org> <CACsn0ckzxMZRN6MxmkUjByzzgbgJdH3eRxVT1dA37TYQHeUq2Q%mail.gmail.com@mailhub.eait.uq.edu.au> <461a8358-8bd8-4f45-f8f3-073f993fb18f@mindrot.org> <ba9669a6-65a6-4276-8306-bd55ef0d146f@app.fastmail.com> <534410e1-5a26-f610-ba68-1f0595ab7a64@mindrot.org> <a1321119-137e-ae67-d65b-ea0cdc4af9d2@mindrot.org> <867cbc77-a08c-40d4-b665-75939eab065a@dennis-jackson.uk>
OpenPGP: id=B1D2BD1375BECB784CF4F8C4D73CF638C53C06BE; url=https://josefsson.org/key-20190320.txt
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Date: Wed, 29 Apr 2026 20:16:09 +0200
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Subject: [Ssh] Re: Supporting pure ML-DSA as hostkey and authkey
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Dennis Jackson <ietf=40dennis-jackson.uk@dmarc.ietf.org> writes:

> On 29/04/2026 17:54, Damien Miller wrote:
>
>>> CA signatures frequently last years or decades.
>>>
> For signatures & public keys that we trust, yes, but we can and do
> withdraw trust from ones which have become suspect much more quickly.
>
> There's no analogue operation for 'revoking' a past encryption to a
> now-broken public key cryptosystem. That's why confidentiality matters
> pretty much indefinitely, but authentication only matters until you
> can ship an update to your clients.

That's backwards.  Updates to clients needs to be authenticated,
otherwise anyone can send you a rogue update.  Authenticated with what,
you ask?  Well, often a signature, and it may be a SSH signature (some
projects are moving to use SSH signing for artifact protection).  You
can't have encryption between Alice and Bob without authentication,
that's crypto 101.

/Simon

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