Re: [lamps] Revocation Request Format?

Peter Bowen <pzbowen@gmail.com> Fri, 02 March 2018 20:03 UTC

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From: Peter Bowen <pzbowen@gmail.com>
Date: Fri, 2 Mar 2018 12:03:29 -0800
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To: Ryan Sleevi <ryan-ietf@sleevi.com>
Cc: Phillip Hallam-Baker <phill@hallambaker.com>, SPASM <SPASM@ietf.org>
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Subject: Re: [lamps] Revocation Request Format?
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On Fri, Mar 2, 2018 at 8:08 AM, Ryan Sleevi <ryan-ietf@sleevi.com> wrote:
> It seems signing a new CSR has been a common practice as proof of
> possession.
>
> There's one segment of users that want to have a time-constrained request
> (that is, incorporating a challenge/response), while another would prefer
> that you can generate the 'request to revoke' at the same time you request
> the cert, so that you can use this token for situations such as loss of
> private key (but not loss of revocation token)
>
> It doesn't seem like there needs to be a bespoke format here, considering
> that the industry is still working through its use cases, and any signed
> data is sufficient.
>
> Further, it may do harm to try and standardize that. Consider the ROBOT
> attack ( https://robotattack.org/ ), which presented a signing oracle with
> TLS private keys. Prematurely constraining revocation requests to a
> particular format might otherwise preclude reasonable demonstration of
> private key compromise.
>
> So I don't think there's anything for LAMPS to do here - we have ample
> available technology (running code that already works) and we have not yet
> ascertained industry needs in any meaningful way (no rough consensus for
> something new)

There is also a documented (albeit not in RFCs) format for a generic
signed public key with challenge:
https://www.w3.org/TR/html51/sec-forms.html#the-keygen-element

PublicKeyAndChallenge ::= SEQUENCE {
  spki SubjectPublicKeyInfo,
  challenge IA5STRING
}

SignedPublicKeyAndChallenge ::= SEQUENCE {
  publicKeyAndChallenge PublicKeyAndChallenge,
  signatureAlgorithm AlgorithmIdentifier,
  signature BIT STRING
}

The challenge is an arbitrary length IA5STRING, so it could easily
include nonce or other challenge data to prove key control.

Thanks,
Peter