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Date:   Sun, 12 Jul 2020 21:02:32 +0300
From:   Vitaly Chikunov <vt@altlinux.org>
To:     Stephan =?utf-8?Q?M=C3=BCller?= <smueller@chronox.de>
Cc:     herbert@gondor.apana.org.au, linux-crypto@vger.kernel.org,
        Marcelo Cerri <marcelo.cerri@canonical.com>,
        Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
        ard.biesheuvel@linaro.org, nhorman@redhat.com, simo@redhat.com
Subject: Re: [PATCH v2 1/5] crypto: ECDH - check validity of Z before export
Message-ID: <20200712180232.jnvkz6xtx63hisvg@altlinux.org>
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        Tianjia Zhang <tianjia.zhang@linux.alibaba.com>,
        ard.biesheuvel@linaro.org, nhorman@redhat.com, simo@redhat.com
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On Sun, Jul 12, 2020 at 06:39:26PM +0200, Stephan Müller wrote:
> SP800-56A rev3 section 5.7.1.2 step 2 mandates that the validity of the
> calculated shared secret is verified before the data is returned to the
> caller. Thus, the export function and the validity check functions are
> reversed. In addition, the sensitive variables of priv and rand_z are

Reviewed-by: Vitaly Chikunov <vt@altlinux.org>

> zeroized.
> 
> Signed-off-by: Stephan Mueller <smueller@chronox.de>
> ---
>  crypto/ecc.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/crypto/ecc.c b/crypto/ecc.c
> index 02d35be7702b..52e2d49262f2 100644
> --- a/crypto/ecc.c
> +++ b/crypto/ecc.c
> @@ -1495,11 +1495,16 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
>  
>  	ecc_point_mult(product, pk, priv, rand_z, curve, ndigits);
>  
> -	ecc_swap_digits(product->x, secret, ndigits);
> -
> -	if (ecc_point_is_zero(product))
> +	if (ecc_point_is_zero(product)) {
>  		ret = -EFAULT;
> +		goto err_validity;
> +	}
> +
> +	ecc_swap_digits(product->x, secret, ndigits);
>  
> +err_validity:
> +	memzero_explicit(priv, sizeof(priv));
> +	memzero_explicit(rand_z, sizeof(rand_z));
>  	ecc_free_point(product);
>  err_alloc_product:
>  	ecc_free_point(pk);
> -- 
> 2.26.2
> 
> 
>