Thank you for your review. I think most of your suggestions are good, but
have a few comments.

> Use short-lived certificates

This doesn't make sense to me. A short lived cert will be permanently
logged in CT.
In fact using shorter certs means more entries for the onion service in the
CT log - making it easier, not harder, to find.

> Use a separate domain/key pair

This goes counter to the whole idea of a PKI. Using a cert for a.onion on
b.onion asserts very little useful.

> CT Exemption Advocacy

I don't think an RFC is the place to advocate for changes in a different
organization, but otherwise agreed.

I will incorporate the rest of your comments as appropriate.
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On Fri, 29 Nov 2024 at 19:22, Derrell Piper via Datatracker <
[email protected]> wrote:

> Reviewer: Derrell Piper
> Review result: Has Nits
>
> I have reviewed this document as part of the security directorate's
> ongoing effort to review all IETF documents being processed by the IESG.
> These comments were written primarily for the benefit of the security
> area directors.  Document editors and WG chairs should treat these
> comments just like any other last call comments.
>
> The summary of the review is Ready With Nits
>
> My concern remains with the privacy risks of CT logs with onion
> services.  CT aims to improve TLS security but creates tensions with the
> anonymity expected from onion services.  So let me suggest some possible
> mitigation text for the Security Considerations section without fully
> understanding ACME or Tor.
>
> Use short-lived certificates: Request certificates with a short validity
> period, such as 90 days or less. This reduces the window of exposure in
> CT logs. You'll need to renew certificates more frequently, but it
> limits the privacy impact.
>
> Avoid unnecessary certificate requests: Only request publicly-trusted
> certificates for onion services that truly need them, such as those
> serving websites to the general public (e.g. SecureDrop or news
> outlets). For internal or non-public services, consider using
> self-signed or privately-trusted certificates that don't get logged to
> public CT.
>
> Use a separate domain/key pair: Register a distinct .onion address for
> the specific purpose of obtaining a certificate, instead of using your
> primary service's domain. This separates the publicly logged certificate
> from your main onion service.
>
> Obfuscate subscriber information: When requesting certificates, provide
> minimal or obfuscated subscriber details to the CA if possible, such as
> a pseudonymous email address or entity name. The CA/Browser Forum
> Baseline Requirements allow some flexibility here.  But obfuscating
> subscriber info with pseudonyms only reduces casual exposure but doesn't
> guarantee anonymity, as CAs likely keep records mapping pseudonyms to
> real identities.
>
> Monitor CT logs: Proactively monitor CT logs for certificates issued for
> your onion domain(s). This can help detect any mis-issuance or
> unauthorized certificates. Some CAs and third-party services offer CT
> monitoring.
>
> Use ACME account key privacy: When using ACME, generate a new account
> key pair for each .onion domain and avoid re-using keys across
> domains. This reduces the ability to correlate multiple domains to a
> single owner based on account keys.
>
> Private certificate authorities: For clusters of related onion services,
> consider setting up a private CA that isn't constrained by the CT
> logging requirement of public trust. This avoids any exposure in public
> CT logs.  Obvoiusly this is only viaable for larger onion service
> deployments given the additional technical overhead.  They aren't
> feasible for all clusters of related services.
>
> Inform .onion Operators of CT Risks: ACME clients targeting .onion
> domains should include explicit warnings about CT logging implications
> to ensure operators make informed decisions.
>
> CT Exemption Advocacy: Advocate for discussions within the CA/Browser
> Forum on potential CT exemptions for .onion services, given their unique
> anonymity requirements. This could be accompanied by alternative
> transparency mechanisms tailored to .onion ecosystems.
>
> Exploration of Private CT Logs: Research and development into private CT
> logs or trusted third-party logging mechanisms for .onion services may
> offer a compromise between transparency and privacy.
>
>
>
>
>
>
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