Re: Public keys and key usage

Honest question: What's the use case?

It's a public key. Restricting the usage offers no practical security
benefit; the key is public.
It's like having an unextractable public key: What would that even mean?

I would rather have asymmetry, but with security benefits (such as
enforcing usages on private keys, to prevent everything from key disclosure
issues to cross-protocol attacks), than to try to offer symmetry of
enforcement but with demonstrably circumventable security (export public
key, re-import it with new usages)

I would argue that it's a bug that publicKeys can be marked non-extractable
at all (via importKey/unwrapKey's generic steps), since the asymmetric key
types (RSA, ECDSA, ECDH) *always* set the public key to be extractable.

On Mon, Nov 16, 2015 at 9:00 PM, Jim Schaad <ietf@augustcellars.com> wrote:

> I totally understand that, however my question would be why cannot not use
> the deriveKey and deriveBits on the public key in order to restrict their
> usage as well.  If I send you a public key and you use it to do deriveBits
> and I don’t support that usage there is no enforcement of that at the
> present time.
>
>
>
> I do not object to the fact that a public key can have no usages, just
> wondering if it really makes sense to say that is the only  valid option.
> There would need to be some potential questions dealing with generation of
> public keys.
>
>
>
> I note that there are different usages set for the RSA keys, just not for
> the key agreement algorithms.
>
>
>
> Jim
>
>
>
>
>
> *From:* Eric Roman [mailto:ericroman@google.com]
> *Sent:* Monday, November 16, 2015 1:57 PM
> *To:* Jim Schaad <ietf@augustcellars.com>
> *Cc:* Ryan Sleevi <sleevi@google.com>; public-webcrypto@w3.org
> *Subject:* Re: Public keys and key usage
>
>
>
> I didn't search the mailinglist archives, but here are some relevant
> discussions on bug threads:
>
>
>
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=26413 says that keys
> should only be allowed to be created with usages that are applicable to the
> particular algorithm and key type.
>
>
>
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=25820: says that empty
> usages should not be allowed for private/secret keys, but makes an
> allowance for public keys.
>
>
>
> From the way ECDH defines the deriveKey and deriveBits in terms of the
> private key (with public key just another parameter of the algorithm) it
> follows that the private key can have deriveBits/deriveKey usage. But there
> is no corresponding usage enforced for public keys. The only option then is
> for their usages to be empty, since invalid usages for keys are not allowed
> per that first bug.
>
>
>
> On Mon, Nov 16, 2015 at 1:18 PM, Jim Schaad <ietf@augustcellars.com>
> wrote:
>
> Ryan,
>
> I did a quick search of my mail box and could not find the reasoning for
> forcing public ECDH keys to have an empty usage field.  Was there one or
> was it never discussed?
>
> Jim
>
>
>
>
>