[PATCH] SoC: cros_ec_codec: switch to library API for SHA-256

[Ard Biesheuvel]

On Fri, 15 May 2020 at 04:40, Tzung-Bi Shih <tzungbi at google.com> wrote:
>
> On Fri, May 15, 2020 at 12:26 AM Benson Leung <bleung at google.com> wrote:
> > On Thu, May 14, 2020 at 06:18:47PM +0200, Ard Biesheuvel wrote:
> > > The CrOS EC codec driver uses SHA-256 explicitly, and not in a
> > > performance critical manner, so there is really no point in using
> > > the dynamic SHASH crypto API here. Let's switch to the library API
> > > instead.
>
> Pardon me if I don't understand it precisely.  What is the difference
> between the two APIs?  Suppose it should calculate the same SHA256
> hash with the same binary blob after switching to library API?
>

Yes.

> > > Looking at the code, I was wondering if the SHA-256 is really required
> > > here? It looks like it is using it as some kind of fingerprint to decide
> > > whether the provided file is identical to the one that has already been
> > > loaded. If this is the case, we should probably just use CRC32 instead.
>
> No, the binary blob carries data and possibly code.  We are not only
> using the hash as a fingerprint but also an integrity check.
>

But does it have to be cryptographically strong? Why is CRC32 not sufficient?

> > > Also, do we really need to wipe the context struct? Is there any security
> > > sensitive data in there?
>
> No, not necessary as far as I know.

OK