Re: [PATCH v2 2/2] certs: Add support for using elliptic curve keys for signing modules

[Jessica Yu]

+++ Stefan Berger [20/04/21 17:02 -0400]:
> On 4/20/21 10:03 AM, Jessica Yu wrote:
> > +++ Stefan Berger [08/04/21 11:24 -0400]:
> > > diff --git a/crypto/asymmetric_keys/pkcs7_parser.c 
> > > b/crypto/asymmetric_keys/pkcs7_parser.c
> > > index 967329e0a07b..2546ec6a0505 100644
> > > --- a/crypto/asymmetric_keys/pkcs7_parser.c
> > > +++ b/crypto/asymmetric_keys/pkcs7_parser.c
> > > @@ -269,6 +269,10 @@ int pkcs7_sig_note_pkey_algo(void *context, 
> > > size_t hdrlen,
> > >         ctx->sinfo->sig->pkey_algo = "rsa";
> > >         ctx->sinfo->sig->encoding = "pkcs1";
> > >         break;
> > > +    case OID_id_ecdsa_with_sha256:
> > > +        ctx->sinfo->sig->pkey_algo = "ecdsa";
> > > +        ctx->sinfo->sig->encoding = "x962";
> > > +        break;
> >
> > Hi Stefan,
> >
> > Does CONFIG_MODULE_SIG_KEY_TYPE_ECDSA have a dependency on 
> > MODULE_SIG_SHA256?
>
> You are right, per the code above it does have a dependency on SHA256. 
> ECDSA is using NIST p384 (secp384r1) for signing and per my tests it 
> can be paired with all the sha hashes once the code above is extended. 
> Now when it comes to module signing, should we pair it with a 
> particular hash? I am not currently aware of a guidance document on 
> this but sha256 and sha384 seem to be good choices these days, so 
> maybe selecting ECDSA module signing should have a 'depends on' on 
> these?

Yeah, I would tack on the 'depends on' until the code above has been
extended to cover more sha hashes - because currently if someone
builds and signs a bunch of modules with an ECDSA key, they will fail
to load if they picked something other than sha256. I am unfortunately
not knowledgeable enough to suggest an official guideline on choice of
hash, but for now it is reasonable to have a 'depends on' for which
hashes the code currently supports, so that users don't run into
module loading rejection issues.

Thanks!

Jessica