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Date: Mon, 27 May 2024 20:34:08 +0300
Message-Id: <D1KLVVIGOUSM.27M0JU1DIX0FN@kernel.org>
Subject: Re: ecdsa_set_pub_key
From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Jarkko Sakkinen" <jarkko@kernel.org>, <linux-crypto@vger.kernel.org>,
 "Stefan Berger" <stefanb@linux.ibm.com>
Cc: "Herbert Xu" <herbert@gondor.apana.org.au>, "David Howells"
 <dhowells@redhat.com>, <keyrings@vger.kernel.org>
References: <D1KLP7ML9T1B.1LHPTTWEANRJ3@kernel.org>
In-Reply-To: <D1KLP7ML9T1B.1LHPTTWEANRJ3@kernel.org>

On Mon May 27, 2024 at 8:25 PM EEST, Jarkko Sakkinen wrote:
> Hi,
>
> The documentation of ecdsa_set_pub_key() is the following:
>
> /*
>  * Set the public key given the raw uncompressed key data from an X509
>  * certificate. The key data contain the concatenated X and Y coordinates=
 of
>  * the public key.
>  */
>
> If you interpret this literally it would mean 64 bytes buffer for p256
> with two 32 byte blobs for x and y.
>
> With such buffer the function fails with -EINVAL, which is obvious from
> the code that does checks on the contents.
>
> Instead of responding to this, can you please fix the documentation bug?
>
> There was also badly documented stuff in akcipher that has been
> unreacted so far so putting also that one here:
>
> https://lore.kernel.org/keyrings/D1HCVOZ1IN7S.1SUZ75QRE8QUZ@kernel.org/
>
> BR, Jarkko

The best reference I could quickly find is Wikipedia:

"The older uncompressed keys are 65 bytes, consisting of constant prefix
(0x04), followed by two 256-bit integers called x and y (2 * 32 bytes).
The prefix of a compressed key allows for the y value to be derived from
the x value."

The documentation says absolutely nothing about the prefix byte, and
neither Wikipedia nor kernel documentation has a reference to this
"older format".

BR, Jarkko