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Date:   Mon, 17 Jan 2022 11:59:33 -0500
From:   Konstantin Ryabitsev <konstantin@linuxfoundation.org>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Roberto Sassu <roberto.sassu@huawei.com>, dhowells@redhat.com,
        dwmw2@infradead.org, herbert@gondor.apana.org.au,
        davem@davemloft.net, keyrings@vger.kernel.org,
        linux-crypto@vger.kernel.org, linux-integrity@vger.kernel.org,
        linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org,
        zohar@linux.ibm.com, ebiggers@kernel.org
Subject: Re: [PATCH 00/14] KEYS: Add support for PGP keys and signatures
Message-ID: <20220117165933.l3762ppcbj5jxicc@meerkat.local>
References: <20220111180318.591029-1-roberto.sassu@huawei.com>
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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