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

[Stefan Berger]

On 4/21/21 8:52 AM, Jessica Yu wrote:
> +++ 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.


I was going to repost this series now with the additional OIDs supported 
above and a recommendation to use sha384 in the help text for 
ECDSA-signed modules, but not enforcing this but instead trusting the 
user that they will choose a reasonable hash (probably >= sha256).


   Stefan


> Thanks!
>
> Jessica