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Date:   Wed, 15 Jul 2020 10:19:12 -0300
From:   Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
To:     Stephan =?utf-8?Q?M=C3=BCller?= <smueller@chronox.de>
Cc:     herbert@gondor.apana.org.au, linux-crypto@vger.kernel.org,
        Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
        ard.biesheuvel@linaro.org, nhorman@redhat.com, simo@redhat.com
Subject: Re: [PATCH v2 5/5] crypto: ECDH SP800-56A rev 3 local public key
 validation
Message-ID: <20200715131912.7enis4arnbs5lewt@valinor>
References: <2543601.mvXUDI8C0e@positron.chronox.de>
 <5722559.lOV4Wx5bFT@positron.chronox.de>
 <3168469.44csPzL39Z@positron.chronox.de>
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Reviewed-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Tested-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>

On Sun, Jul 12, 2020 at 06:42:14PM +0200, Stephan M=FCller wrote:
> After the generation of a local public key, SP800-56A rev 3 section
> 5.6.2.1.3 mandates a validation of that key with a full validation
> compliant to section 5.6.2.3.3.
>=20
> Only if the full validation passes, the key is allowed to be used.
>=20
> The patch adds the full key validation compliant to 5.6.2.3.3 and
> performs the required check on the generated public key.
>=20
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
>  crypto/ecc.c | 31 ++++++++++++++++++++++++++++++-
>  crypto/ecc.h | 14 ++++++++++++++
>  2 files changed, 44 insertions(+), 1 deletion(-)
>=20
> diff --git a/crypto/ecc.c b/crypto/ecc.c
> index 52e2d49262f2..7308487e7c55 100644
> --- a/crypto/ecc.c
> +++ b/crypto/ecc.c
> @@ -1404,7 +1404,9 @@ int ecc_make_pub_key(unsigned int curve_id, unsigne=
d int ndigits,
>  	}
> =20
>  	ecc_point_mult(pk, &curve->g, priv, NULL, curve, ndigits);
> -	if (ecc_point_is_zero(pk)) {
> +
> +	/* SP800-56A rev 3 5.6.2.1.3 key check */
> +	if (ecc_is_pubkey_valid_full(curve, pk)) {
>  		ret =3D -EAGAIN;
>  		goto err_free_point;
>  	}
> @@ -1452,6 +1454,33 @@ int ecc_is_pubkey_valid_partial(const struct ecc_c=
urve *curve,
>  }
>  EXPORT_SYMBOL(ecc_is_pubkey_valid_partial);
> =20
> +/* SP800-56A section 5.6.2.3.3 full verification */
> +int ecc_is_pubkey_valid_full(const struct ecc_curve *curve,
> +			     struct ecc_point *pk)
> +{
> +	struct ecc_point *nQ;
> +
> +	/* Checks 1 through 3 */
> +	int ret =3D ecc_is_pubkey_valid_partial(curve, pk);
> +
> +	if (ret)
> +		return ret;
> +
> +	/* Check 4: Verify that nQ is the zero point. */
> +	nQ =3D ecc_alloc_point(pk->ndigits);
> +	if (!nQ)
> +		return -ENOMEM;
> +
> +	ecc_point_mult(nQ, pk, curve->n, NULL, curve, pk->ndigits);
> +	if (!ecc_point_is_zero(nQ))
> +		ret =3D -EINVAL;
> +
> +	ecc_free_point(nQ);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(ecc_is_pubkey_valid_full);
> +
>  int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigit=
s,
>  			      const u64 *private_key, const u64 *public_key,
>  			      u64 *secret)
> diff --git a/crypto/ecc.h b/crypto/ecc.h
> index ab0eb70b9c09..d4e546b9ad79 100644
> --- a/crypto/ecc.h
> +++ b/crypto/ecc.h
> @@ -147,6 +147,20 @@ int crypto_ecdh_shared_secret(unsigned int curve_id,=
 unsigned int ndigits,
>  int ecc_is_pubkey_valid_partial(const struct ecc_curve *curve,
>  				struct ecc_point *pk);
> =20
> +/**
> + * ecc_is_pubkey_valid_full() - Full public key validation
> + *
> + * @curve:		elliptic curve domain parameters
> + * @pk:			public key as a point
> + *
> + * Valdiate public key according to SP800-56A section 5.6.2.3.3 ECC Full
> + * Public-Key Validation Routine.
> + *
> + * Return: 0 if validation is successful, -EINVAL if validation is faile=
d.
> + */
> +int ecc_is_pubkey_valid_full(const struct ecc_curve *curve,
> +			     struct ecc_point *pk);
> +
>  /**
>   * vli_is_zero() - Determine is vli is zero
>   *
> --=20
> 2.26.2
>=20
>=20
>=20
>=20

--=20
Regards,
Marcelo


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