Re: [saag] Fwd: New Version Notification for draft-belyavskiy-certificate-limitation-policy-04.txt

Dear Nicos,

Sorry for the delay with my response.

On Fri, Sep 22, 2017 at 11:06 AM, Nikos Mavrogiannopoulos <[email protected]>
wrote:

> On Wed, Sep 20, 2017 at 3:21 PM, Dmitry Belyavsky <[email protected]>
> wrote:
> > Dear Nikos
> >
> > On Wed, Sep 13, 2017 at 9:39 AM, Nikos Mavrogiannopoulos <
> [email protected]>
> > wrote:
> >>
> >>
> >> 4. How do you handle extensions to this format?
> >>
> >> Overall, why not use X.509 extensions to store such additional
> >> constraints? We already (in the p11-kit trust store in Fedora/RHEL
> >> systems) use the notion of stapled extensions to limit certificates
> >> [0, 1] and seems quite a flexible approach. Have you considered that
> >> path?
> >>
> >> regards,
> >> Nikos
> >>
> >> [0].
> >> https://p11-glue.freedesktop.org/doc/storing-trust-policy/
> storing-trust-model.html
> >> [1].
> >> http://nmav.gnutls.org/2016/06/restricting-scope-of-ca-
> certificates.html
> > I've looked through the specification. It's OK for me, but I do not get
> > whether the attached extensions are crypto-protected.
>
> No, as these values are inserted by the administrator of the system,
> or us (the distributor of the software), we didn't feel we needed the
> introduction of additional PKI.
>

Well, the specification I suggest should allow applying CLPs issued by
major vendors (Mozilla etc).
For this purposes the CLPs should be validable => signed.



> How do you see the infrastructure on the
> draft-belyavskiy-certificate-limitation-policy? Who do you envision
> signing these structures? (I assume that distribution of data will be
> done by software distributors?)
>

I anticipate some ways to distribute CLPs.

1. Major vendor-issued CLPs are distributed either by vendors or by OS
vendors
(similar to, e.g., ca-certificates package in Debian). In this case we
should have
certificates to sign these CLPs distributed together with these bundles.

2. App-specific CLPs may include the key as a part of the application
bundle.
So CLP is distributed via normal app-distributing channel.

3. Locally created CLPs. This is the case more or less similar to the
p11-glue solution,
if I understand it correctly.

Various protocols, such as TAMP (RFC 5934) can be used for transport the
CLPs too.


>
> >> 4. How do you handle extensions to this format?
> >>
> > Simillary to CRL. Do you have ideas of the extensions?
>
> One problem with that is the fact that the existing CRL extensions are
> about extending attributes of the CRL, rather than adding/removing
> attributes to the certificate in question.
>

For this purposes I implied that the limitations are provided not by
extensions,
but as SEQUENCE of limitations related to the certificates.

Was I wrong in the ASN1 scheme in the current version of my draft?



> To bring the stapled extensions to your proposal, you'd need the
> Extensions and Extension fields from RFC5280, and
> add into limitedCertificates structure (I'll split it on the example
> below for clarity) the following field.
>
> LimitedCertificates  ::=   SEQUENCE OF LimitedCertificate
>
> LimitedCertificate ::= SEQUENCE {
>                 userCertificate         CertificateSerialNumber,
>                 certificateIssuer       Name,
>                 limitationDate          Time,
>                 limitationPropagation   Enum,
>                 fingerprint SEQUENCE {
>                     fingerprintAlgorithm AlgorithmIdentifier,
>                     fingerprintValue     OCTET STRING
>                                      } OPTIONAL,
>                 limitations          SEQUENCE,
>                                    } OPTIONAL,
>                                  };
>
>
>                 stapledExtensions Extensions; <----- NEW
> }
>

Sorry, I do not get the difference between the purposes of the field
'limitations'
and 'stapledExtensions'.


> Another difference between this profile and the p11-kit one, is that
> the extensions/revocation here is done on the certificate, while in
> p11-kit is done on the public key. Both approaches have pros and cons.
>

Sure.


>
> Another question. I also noticed the fingerprint field above. Is that
> to distinguish between same CAs with different keys? In that case
> using the SubjectPublicKeyIdentifier may be sufficient, and more
> natural as this is how certificates with matching DNs/serials are
> distinguished.
>

Do you mean Subject Key Identifier (RFC 5280, 4.2.1.2)?
Yes, I agree and I'll update the draft.

I introduced the fingerprint field to distinguish bogus certs from the
valid ones,
but I think the SKI will be OK for this purpose.

Thank you!

-- 
SY, Dmitry Belyavsky

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