linux-kernel - Re: [PATCH 00/14] KEYS: Add support for PGP keys and signatures

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Date:   Mon, 17 Jan 2022 11:59:33 -0500
From:   Konstantin Ryabitsev <konstantin@...uxfoundation.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Roberto Sassu <roberto.sassu@...wei.com>, dhowells@...hat.com,
        dwmw2@...radead.org, herbert@...dor.apana.org.au,
        davem@...emloft.net, keyrings@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-fscrypt@...r.kernel.org, linux-kernel@...r.kernel.org,
        zohar@...ux.ibm.com, ebiggers@...nel.org
Subject: Re: [PATCH 00/14] KEYS: Add support for PGP keys and signatures

On Mon, Jan 17, 2022 at 03:34:54PM +0100, Jason A. Donenfeld wrote:
> If you're looking for a simple signature mechanism to replace the use of
> X.509 and all of that infrastructure, may I suggest just coming up with
> something simple using ed25519, similar to signify or minisign? Very
> minimal code in the kernel, in userspace, and very few moving parts to
> break.

I am concerned that ed25519 private key management is very rudimentary -- more
often than not it is just kept somewhere on disk, often without any passphrase
encryption.

With all its legacy warts, GnuPG at least has decent support for hardware
off-load via OpenPGP smartcards or TPM integration in GnuPG 2.3, but the best
we have with ed25519 is passhprase protection as implemented in minisign (and
even that is rudimentary -- if you need to sign 10 things, you will need to
type in your passphrase 10 times, as there is no passphrase agent of any
kind).

The most promising non-PGP development of PKI signatures that I've seen lately
is the openssh FIDO2 integration (the -sk keys) and support for
signing/verifying arbitrary external content using `ssh-keygen -n`. It even
does fairly sane things with identity/revocation/expiration via its
allowed_signers implementation, even if I'm less excited about it all being in
a single file.

Everything else is just treating key management as something out of scope, and
I'm worried that it's going to result in a net loss in overall security.

-K