linux-kernel - Re: [PATCH v6 03/13] crypto: ecdsa - Adjust tests on length of key parameters

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Date: Mon, 18 Mar 2024 22:25:26 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Stefan Berger" <stefanb@...ux.vnet.ibm.com>,
 <keyrings@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
 <herbert@...dor.apana.org.au>, <davem@...emloft.net>
Cc: <linux-kernel@...r.kernel.org>, <saulo.alessandre@....jus.br>,
 <lukas@...ner.de>, <bbhushan2@...vell.com>, "Stefan Berger"
 <stefanb@...ux.ibm.com>
Subject: Re: [PATCH v6 03/13] crypto: ecdsa - Adjust tests on length of key
 parameters

On Tue Mar 12, 2024 at 8:36 PM EET, Stefan Berger wrote:
> From: Stefan Berger <stefanb@...ux.ibm.com>
>
> In preparation for support of NIST P521, adjust the basic tests on the
> length of the provided key parameters to only ensure that the length of the
> x plus y coordinates parameter array is not an odd number and that each
> coordinate fits into an array of 'ndigits' digits. Mathematical tests on
> the key's parameters are then done in ecc_is_pubkey_valid_full rejecting
> invalid keys.
>
> The change is necessary since NIST P521 keys do not have keys with
> coordinates that each fully require 'full' digits (= u64), unlike
> NIST P192/256/384 that all require multiple 'full' digits.

This sentence is not really comprehendable English sentence. Can you
just write the rationale in understandable form?

"fully require full digits (= u64)" is something totally alien to me
tbh.

>
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> Tested-by: Lukas Wunner <lukas@...ner.de>
> ---
>  crypto/ecdsa.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/crypto/ecdsa.c b/crypto/ecdsa.c
> index 6653dec17327..64e1e69d53ba 100644
> --- a/crypto/ecdsa.c
> +++ b/crypto/ecdsa.c
> @@ -230,7 +230,7 @@ static int ecdsa_set_pub_key(struct crypto_akcipher *tfm, const void *key, unsig
>  	if (ret < 0)
>  		return ret;
>  
> -	if (keylen < 1 || (((keylen - 1) >> 1) % sizeof(u64)) != 0)
> +	if (keylen < 1 || ((keylen - 1) & 1) != 0)
>  		return -EINVAL;
>  	/* we only accept uncompressed format indicated by '4' */
>  	if (d[0] != 4)


BR, Jarkko