linux-kernel - Re: [PATCH v7 03/13] crypto: ecdsa - Adjust tests on length of key parameters

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Message-Id: <CZZLG1NOKZED.3VQXFGK57IEEU@kernel.org>
Date: Thu, 21 Mar 2024 19:11:30 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Stefan Berger" <stefanb@...ux.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>
Subject: Re: [PATCH v7 03/13] crypto: ecdsa - Adjust tests on length of key
 parameters

On Wed Mar 20, 2024 at 1:47 PM EET, Stefan Berger wrote:
> 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 require 'full' digits (= all bits in u64 used).
> NIST P521 only requires 2 bytes (9 bits) in the most significant digit
> unlike NIST P192/256/384 that each require multiple 'full' digits.
>
> 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)

Had to write this down to the paper to fully get it but yeah makes
sense (especially since I just truncated 4 KiB blocks to 1 KiB
in my doc update :-)) but yeah seems to be correct:


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

I guess that in this case I can give also tested-by since I actually
did test the formula (on paper):

Tested-by: Jarkko Sakkinen <jarkko@...nel.org>

As in general for tested-by's for patches I've sent or seen in
circulation there's bunch of convetions I've encountered so I do
agree that it is up to Herbert to decide the correct one.

BR, Jarkko