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Date:   Wed, 15 Jul 2020 10:17:58 -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 3/5] crypto: DH - check validity of Z before export
Message-ID: <20200715131758.mbiro6hyahsfrrew@valinor>
References: <2543601.mvXUDI8C0e@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 06:40:20PM +0200, Stephan M=FCller wrote:
> SP800-56A rev3 section 5.7.1.1 step 2 mandates that the validity of the
> calculated shared secret is verified before the data is returned to the
> caller. This patch adds the validation check.
>=20
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
>  crypto/dh.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>=20
> diff --git a/crypto/dh.c b/crypto/dh.c
> index 566f624a2de2..f84fd50ec79b 100644
> --- a/crypto/dh.c
> +++ b/crypto/dh.c
> @@ -9,6 +9,7 @@
>  #include <crypto/internal/kpp.h>
>  #include <crypto/kpp.h>
>  #include <crypto/dh.h>
> +#include <linux/fips.h>
>  #include <linux/mpi.h>
> =20
>  struct dh_ctx {
> @@ -179,6 +180,34 @@ static int dh_compute_value(struct kpp_request *req)
>  	if (ret)
>  		goto err_free_base;
> =20
> +	/* SP800-56A rev3 5.7.1.1 check: Validation of shared secret */
> +	if (fips_enabled && req->src) {
> +		MPI pone;
> +
> +		/* z <=3D 1 */
> +		if (mpi_cmp_ui(val, 1) < 1) {
> +			ret =3D -EBADMSG;
> +			goto err_free_base;
> +		}
> +
> +		/* z =3D=3D p - 1 */
> +		pone =3D mpi_alloc(0);
> +
> +		if (!pone) {
> +			ret =3D -ENOMEM;
> +			goto err_free_base;
> +		}
> +
> +		ret =3D mpi_sub_ui(pone, ctx->p, 1);
> +		if (!ret && !mpi_cmp(pone, val))
> +			ret =3D -EBADMSG;
> +
> +		mpi_free(pone);
> +
> +		if (ret)
> +			goto err_free_base;
> +	}
> +
>  	ret =3D mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
>  	if (ret)
>  		goto err_free_base;
> --=20
> 2.26.2
>=20
>=20
>=20
>=20

--=20
Regards,
Marcelo


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