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Date: Mon, 18 Mar 2024 22:50:11 +0200
Message-Id: <CZX67UDST7WU.1LNVWGY9DM999@kernel.org>
From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Stefan Berger" <stefanb@linux.vnet.ibm.com>,
 <keyrings@vger.kernel.org>, <linux-crypto@vger.kernel.org>,
 <herbert@gondor.apana.org.au>, <davem@davemloft.net>
Cc: <linux-kernel@vger.kernel.org>, <saulo.alessandre@tse.jus.br>,
 <lukas@wunner.de>, <bbhushan2@marvell.com>, "Stefan Berger"
 <stefanb@linux.ibm.com>
Subject: Re: [PATCH v6 07/13] crypto: ecc - Add special case for NIST P521
 in ecc_point_mult
References: <20240312183618.1211745-1-stefanb@linux.vnet.ibm.com>
 <20240312183618.1211745-8-stefanb@linux.vnet.ibm.com>
In-Reply-To: <20240312183618.1211745-8-stefanb@linux.vnet.ibm.com>

On Tue Mar 12, 2024 at 8:36 PM EET, Stefan Berger wrote:
> From: Stefan Berger <stefanb@linux.ibm.com>
>
> In ecc_point_mult use the number of bits of the NIST P521 curve + 2. The
> change is required specifically for NIST P521 to pass mathematical tests
> on the public key.
>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> Tested-by: Lukas Wunner <lukas@wunner.de>
> ---
>  crypto/ecc.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/crypto/ecc.c b/crypto/ecc.c
> index 99d41887c005..ead40b5ebb46 100644
> --- a/crypto/ecc.c
> +++ b/crypto/ecc.c
> @@ -1320,7 +1320,10 @@ static void ecc_point_mult(struct ecc_point *resul=
t,
>  	carry =3D vli_add(sk[0], scalar, curve->n, ndigits);
>  	vli_add(sk[1], sk[0], curve->n, ndigits);
>  	scalar =3D sk[!carry];
> -	num_bits =3D sizeof(u64) * ndigits * 8 + 1;
> +	if (curve->nbits =3D=3D 521)	/* NIST P521 */
> +		num_bits =3D curve->nbits + 2;
> +	else
> +		num_bits =3D sizeof(u64) * ndigits * 8 + 1;
> =20
>  	vli_set(rx[1], point->x, ndigits);
>  	vli_set(ry[1], point->y, ndigits);


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko