Re: [PATCH v3 00/10] Add support for NIST P521 to ecdsa

Lukas Wunner
2024-02-29T09:34:21Z

On Fri, Feb 23, 2024 at 03:41:39PM -0500, Stefan Berger wrote:
> This series adds support for the NIST P521 curve to the ecdsa module.
>
> An issue with the current code in ecdsa is that it assumes that input
> arrays providing key coordinates for example, are arrays of digits
> (a 'digit' is a 'u64'). This works well for all currently supported
> curves, such as NIST P192/256/384, but does not work for NIST P521 where
> coordinates are 8 digits + 2 bytes long. So some of the changes deal with
> converting byte arrays to digits and adjusting tests on input byte
> array lengths to tolerate arrays not providing multiples of 8 bytes.

Don't you also need to amend software_key_query()? In the "issig" case,
it calculates len = crypto_sig_maxsize(sig), which is 72 bytes for P521,
then further below calculates "info->max_sig_size = 2 * (len + 3) + 2;"

I believe the ASN.1 encoded integers are just 66 bytes instead of 72,
so info->max_sig_size is 6 bytes too large. Am I missing something?

Thanks,

Lukas