Received-SPF: pass (google.com: domain of linux-crypto+bounces-4483-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Precedence: bulk
Mime-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=UTF-8
Date: Wed, 29 May 2024 02:09:45 +0300
Message-Id: <D1LNNE1FMDBS.3T9J17BAX1D04@kernel.org>
To: "Jarkko Sakkinen" <jarkko@kernel.org>, "Herbert Xu"
 <herbert@gondor.apana.org.au>
Cc: <linux-integrity@vger.kernel.org>, <keyrings@vger.kernel.org>,
 <Andreas.Fuchs@infineon.com>, "James Prestwood" <prestwoj@gmail.com>,
 "David Woodhouse" <dwmw2@infradead.org>, "Eric Biggers"
 <ebiggers@kernel.org>, "James Bottomley"
 <James.Bottomley@hansenpartnership.com>, <linux-crypto@vger.kernel.org>,
 "Stefan Berger" <stefanb@linux.ibm.com>, "Lennart Poettering"
 <lennart@poettering.net>, "David S. Miller" <davem@davemloft.net>, "open
 list" <linux-kernel@vger.kernel.org>, "David Howells"
 <dhowells@redhat.com>, "Peter Huewe" <peterhuewe@gmx.de>, "Jason Gunthorpe"
 <jgg@ziepe.ca>, "James Bottomley" <James.Bottomley@HansenPartnership.com>,
 "Ard Biesheuvel" <ardb@kernel.org>, "Mario Limonciello"
 <mario.limonciello@amd.com>
Subject: Re: [PATCH v7 5/5] keys: asymmetric: Add tpm2_key_ecdsa
From: "Jarkko Sakkinen" <jarkko@kernel.org>
References: <20240528210823.28798-1-jarkko@kernel.org>
 <20240528210823.28798-6-jarkko@kernel.org>
 <D1LLSAS0YN47.18EIHL1KRF2UR@kernel.org>
In-Reply-To: <D1LLSAS0YN47.18EIHL1KRF2UR@kernel.org>

On Wed May 29, 2024 at 12:42 AM EEST, Jarkko Sakkinen wrote:
> On Wed May 29, 2024 at 12:08 AM EEST, Jarkko Sakkinen wrote:
> > +	/* Encode the ASN.1 signature: */
> > +#define TPM2_KEY_ECDSA_SIG_SIZE		(2 + 2 * (2 + SHA256_DIGEST_SIZE) + r=
_0 + s_0)
> > +	pr_info("sig_size=3D%d\n", TPM2_KEY_ECDSA_SIG_SIZE);
> > +	ptr[0] =3D 0x30; /* SEQUENCE */
> > +	ptr[1] =3D TPM2_KEY_ECDSA_SIG_SIZE - 2;
> > +#define TPM2_KEY_ECDSA_SIG_R_TAG	2
> > +#define TPM2_KEY_ECDSA_SIG_R_SIZE	3
> > +#define TPM2_KEY_ECDSA_SIG_R_BODY	4
> > +	ptr[TPM2_KEY_ECDSA_SIG_R_TAG] =3D 0x02; /* INTEGER */
> > +	ptr[TPM2_KEY_ECDSA_SIG_R_SIZE] =3D SHA256_DIGEST_SIZE + r_0;
> > +	ptr[TPM2_KEY_ECDSA_SIG_R_BODY] =3D 0x00; /* maybe dummy write */
> > +	memcpy(&ptr[TPM2_KEY_ECDSA_SIG_R_BODY + r_0], r, SHA256_DIGEST_SIZE);
> > +#define TPM2_KEY_ECDSA_SIG_S_TAG	(4 + r_0 + SHA256_DIGEST_SIZE)
> > +#define TPM2_KEY_ECDSA_SIG_S_SIZE	(5 + r_0 + SHA256_DIGEST_SIZE)
> > +#define TPM2_KEY_ECDSA_SIG_S_BODY	(6 + r_0 + SHA256_DIGEST_SIZE)
> > +	ptr[TPM2_KEY_ECDSA_SIG_S_TAG] =3D 0x02; /* INTEGER */
> > +	ptr[TPM2_KEY_ECDSA_SIG_S_SIZE] =3D SHA256_DIGEST_SIZE + s_0;
> > +	ptr[TPM2_KEY_ECDSA_SIG_S_BODY] =3D 0x00; /* maybe dummy write */
> > +	memcpy(&ptr[TPM2_KEY_ECDSA_SIG_S_BODY + s_0], s, SHA256_DIGEST_SIZE);
> > +	ret =3D TPM2_KEY_ECDSA_SIG_SIZE;
>
> Stefan, so this how I realized the signature encoding, thanks to
> your earlier remarks [1]! I found out based on that a few glitches
> and ended up with this better structured ECDSA signature encoder,
> so thank you for doing that.

1. SHA384 would fit without any significant changes.
2. SHA512 will require a single additional byte, i.e. prefix byte 0x81
   for the sequence (not for coeffients).
3. SM3 similarly is also trivial to add.

Both will be also easy to add later on. I would not enlarge this patch
set from what it is now.

So I think this is pretty well along the lines of:

https://datatracker.ietf.org/doc/draft-woodhouse-cert-best-practice/

BR, Jarkko