Subject: Last Call: Using DNS to securely publish SSH key fingerprints to Proposed Standard

From: The IESG <[email-masked]>
Date: Mon, 05 May 2003 18:09:07 -0400

The IESG has received a request from the Secure Shell Working Group to 
consider Using DNS to securely publish SSH key fingerprints 
<draft-ietf-secsh-dns-04.txt> as a Proposed Standard.  

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action.  Please send any comments to the 
[email-masked] or [email-masked] mailing lists by 2003-5-19.

Files can be obtained via http://www.ietf.org/internet-drafts/draft-ietf-secsh-dns-04.txt

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From: Simon Josefsson <[email-masked]>
Date: Mon, 12 May 2003 22:01:55 +0200

Was it considered to allow for other security mechanisms to
authenticate the SSHFP data, besides DNSSEC?  The document says:

   2.4 Authentication

   A public key verified using this method MUST only be trusted if the
   SSHFP resource record (RR) used for verification was authenticated by
   a trusted SIG RR.

   Clients that do not validate the DNSSEC signatures themselves MUST
   use a secure transport, e.g. TSIG [8], SIG(0) [9] or IPsec [7],
   between themselves and the entity performing the signature
   validation.

This seem to require that DNSSEC is used by at least some entity.

I believe this is an unnecessary restriction, and that SSHFP would be
more useful if it the wording was changed to allow for any secure
mechanism.  The document may mention that it was designed for DNSSEC
and that DNSSEC is the recommended way to authenticate data, but I
believe it should not explicitly preclude other (secure) ways of
authenticating the SSHFP data.

Some scenarios that are precluded by the current text:

* TSIG/IPSEC-protected query to authoritative server with SSHFP.

* TSIG/IPSEC-protected query to trusted server with SSHFP.  (The
  server may have received the data using a secure channel from the
  authoritative server.)

* Using data from zone files received securely out of band.  (E.g.,
  via SSH, or by mail protected by CMS or OpenPGP, from the
  authoritative domain.)

Thanks.

(I searched the SSH mailing list but could not find anything related
to this.  I'd appreciate a pointer if this has discussed before.)

---

From: Jakob Schlyter <[email-masked]>
Date: Mon, 12 May 2003 23:49:06 +0200 (CEST)

On Mon, 12 May 2003, Simon Josefsson wrote:

> Was it considered to allow for other security mechanisms to authenticate
> the SSHFP data, besides DNSSEC?

yes, but that does not scale.

>   server may have received the data using a secure channel from the

just because the server is authoritative does not mean the data can be
trusted. the entity signing the zonefile is what should be trusted, not
the box serving it.

>   via SSH, or by mail protected by CMS or OpenPGP, from the

what you are describing here is not DNS, it is some other mechanism using
DNS zone files as transport format.

	jakob