Re: [Secdispatch] [EXTERNAL]Re: Clarification Question for the Comment from Eric Rescorla (

Michael Richardson <> Sat, 21 December 2019 22:46 UTC

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From: Michael Richardson <>
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CC: "Panos Kampanakis \(pkampana\)" <>
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Date: Sat, 21 Dec 2019 17:46:30 -0500
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Subject: Re: [Secdispatch] [EXTERNAL]Re: Clarification Question for the Comment from Eric Rescorla (
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Panos Kampanakis (pkampana) <> wrote:
    > UEFI Secure Boot (in essence what I meant by image singing) uses a PKI
    > architecture. There is a Product Key PK (root CA) that establishes a
    > trust relationship between the platform owner and the platform
    > firmware. The PK signs KEKs which established a trust relationship
    > between the platform firmware and the operating system. These are
    > mostly in X.509 today. More in [2].

    >> Is there a reason why you don't want to do hash signatures?

    > HBS indeed looks like the best option for this usecase. Not necessarily
    > stateful. We have some preliminary analysis on this is in Section 3 in
    > [1].  More to come soon.

    > But we can’t go directly to pure HBS because already deployed machines
    > in the field will not boot at all and upgrading BIOS is not
    > simple. Also, we can’t go to pure HBS because it will not be FIPS
    > approved even after we have a standardized PQ option. So, we have to do
    > some sort of composite RSA+post-quantum (NIST has put out a statement
    > that says that a composite will still be FIPS approved if the classical
    > part is). The FIPS argument is important. Waiting for PQ
    > standardization is one thing, but FIPS approval will take even longer
    > and until then we (Cisco) want to do some sort of composite before
    > then.

okay, I understand now.

You need to have a structure that makes use of all the existing, and
previously validated FIPS mechanisms and structures, but which adds a
post-quantum signature *in addition*.

It seems that such a solution needs to live within the ASN.1/DER-encoded PKIX
rules.   There have been proposals to add a HBS, and the hash-public-keys as
an extension in a certificate, which I think is really ugly, but would work.

I seem to recall a conversation at IETF106 about whether such a thing should
live within the certificate structure, or should wrap it.  It seems that you
need it to live within the certificate structure, and needs to provide a
parallel signature chain.

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