linux-kernel - Re: [PATCH] crypto: ecdsa: Fix the public key format description

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Message-Id: <D1LB8PVCTP1S.JDCEWNODTGTQ@kernel.org>
Date: Tue, 28 May 2024 16:26:22 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Stefan Berger" <stefanb@...ux.ibm.com>, "Herbert Xu"
 <herbert@...dor.apana.org.au>
Cc: <linux-crypto@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] crypto: ecdsa: Fix the public key format description

On Tue May 28, 2024 at 3:37 PM EEST, Stefan Berger wrote:
>      Signature Value:
>          30:45:02:21:00:d9:d7:64:ba:5d:03:07:ee:20:a0:12:16:46:
>          31:e6:8e:66:0c:17:0d:74:07:87:58:5a:13:fc:14:62:98:9a:
>          99:02:20:59:ff:29:9c:52:b9:0a:35:3c:4b:03:bb:47:0e:c8:
>          3e:2d:cb:3e:1c:d3:51:88:91:b1:40:e3:03:86:1b:2a:e8
>
> 30:45 => sequence containing 69 bytes
>    02:21: => first coordinate with 0x21 bytes
>      00:d9 => 0x21 bytes of ASN.1 integer with leading 0 to make the 
> following 0x20-byte integer a positive number (its most significant bit 
> is set).
>    02:20: => int with 0x20 bytes
>     ...

This actually helped me located the bug in my code: I had 32 bytes for
the first one, with no leading zero. I.e. total length was off-by-one.

So I'll just extend either or both based on msb? 

BR, Jarkko