Re: [CFRG] NSA vs. hybrid

[Mike Ounsworth <[e-mail]>]

I don't think the " PQ algorithms do not hold" case is as absolute as you're claiming:


In cold storage encryption or any kind of public trust signature scenario (ie places where record-now-crack-later doesn't apply):
1) Implementation bugs in either traditional or PQC: hybrid makes these not-immediately-fatal and buys you time to patch and potentially re-protect existing data. (applies to both pre- and post-CRQC scenarios thanks to "quantum annoyance").


In all scenarios:
2) Hybrid (esp. with 3+ algs) allows you to combine multiple PQC algs, spreading out your risk.

---
Mike Ounsworth
Software Security Architect, Entrust

-----Original Message-----
From: CFRG <[e-mail]> On Behalf Of Blumenthal, Uri - 0553 - MITLL
Sent: December 6, 2021 6:53 PM
To: Martin Thomson <[e-mail]>; [e-mail]
Subject: [EXTERNAL] Re: [CFRG] NSA vs. hybrid

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______________________________________________________________________
> > For sensitive data, problem (1) is relevant now - because, as you
> > said, ciphertexts could be recorded now and broken/decrypted
> > decade(s) later, when CRQC is available. Hybrid won't help here (and
> > those who don't expect CRQC to arrive, can stay with ECC).
>
> I'm sorry, is that right?  Are you asserting that a hybrid key
> exchange can be broken later?

If our PQ algorithms do not hold - absolutely, Hybrid will be broken with CRQC.

If our PQ algorithms hold - Hybrid holds too, but we don't need it then.

In the end - the fate of Key Exchange rides on whether PQ algorithms will hold.

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