[Syslog] Document shepherd report of AD concerns

["David Harrington" <[e-mail]>]

Hi,

Tom asked for a review of the IESG concerns.
As document shepherd, let me address that question.

This email shows the AD comments as the draft progressed since -11-. 
Some WG input was also taken into consideration during the document
revisions.

Following the publication of -11-, Sam Hartman said:
"Dave, the syslog tls document is much clearer and I think it does a
good job of specifying what implementations need to do.
I think  this is a huge improvement.

However  I have two major problems.

1) The default/recommended configuration requires managed trust
   anchors, a working DNS deployment and certificates provisioned to
   syslog servers.  I do not find it plausible that operators will
   actually do this and so I do not find the specification credible.

2) The spec talks about caching of certificates in a manner similar to
    ssh, but does not discuss operational concerns such as key
    rollover.  Jeff, any chance you could help the syslog working
    group understand the tradeoffs around leap of faith?
"

Jeff Hutzelman provided expert advice on behalf of Sam:
"I can try.  It may be worth noting that I don't think ssh talks much
about 
server key rollover, and it certainly isn't done much in practice.
What 
does happen is server keys changing because of a machine being
reinstalled 
or some similar event.  The approaches open to SSH in that case
(prompt the 
user, or just notify them and fail so they can fix it and try again)
don't 
work so well with syslog, where the originator of a message likely
can't 
fix the problem, and the way to notify the person who can is to send a

syslog message!"

Then the AD token passed from Sam to Pasi, who suggested:
"Here's one idea how to handle certificates for TLS in order to make 
it reasonably secure (in most cases), yet also deployable:

- When a tranport sender configures the address of transport receiver,
and enables TLS, allow the following choices:

  1) configure set of trust anchors, and a name to be matched against
     the cert. If the transport receiver address is configured as DNS
     name, this name would usually be the same one. If the transport
     receiver address is configured as IP address, this one could
     be IP address (but could be also a domain name).

     (Note: in no situation, the result of A/AAAA or PTR lookup
     would be used when checking the certificate. This part of the
     current spec isn't correct.)

  2) configure the "certificate fingerprint" of the peer (typically 
     a 40-digit hex string). Cut-and-pasting that from one SSH window 
     to another isn't the world's friendliest UI, but would be doable
     by admins, and is couple of orders of magnitude less work than 
     setting up a real PKI.

  3) configure "anything goes, don't verify the cert" (obviously,  
     not very secure; SHOULD NOT be done)

- A transport receiver would have similar choices:

  1) configure set of trust anchors, and a list of names (or 
     wildcards matching names) to be matched against the
     certificates; everyone listed here would be OK.

  2) configure list of certificate fingerprints that are OK.

  3) configure list of transport (IP) addresses/netmasks that are 
     allowed to send messages regardless of the certificate
     (obviously, not very secure; SHOULD NOT be done)

- I've intentionally omitted "SSH style leap of faith" (called "MAY
  cache the certificate presented by its peer so it can compare the
  certificate with what is presented in subsequent connections" in
  current spec). .

  It could be added (but has some operational issues); or we could
  specify slightly similar (but not quite) functionality where instead
  of typing in the 40-digit fingerprint, the management interface
  would fetch the fingerprint from the peer, show it to the
administrator,
  and the admin would then compare it against something (e.g., what
  he/she sees in some other SSH window), and confirm that they match.
  There are some issues with this, though.... (user studies made with 
  similar approaches show that most users click "yes, they match" even
  when shown two totally different values).

- We probably need to require that everyone must be able to generate a
  keypair and self-signed certificate, and calculate/display the
  fingerprint of the certificate (in some management interface).

Has something like this (in particular, using the fingerprint in 
cases where deploying PKI isn't feasible) suggested before?  Do 
you think it would be operationally workable?

If you think this might make sense, I can post something on the
mailing list, too. But this is just one preliminary idea -- if 
there are other ideas that would solve the issues, I'm in no way
saying it must be done this way."

Joe did a revision which Paso reviewed, and commented:
"Joe: thanks for working on this; I think we're making good
progress, and I'm optimistic that we could get this draft
done soon.

However, some of the TLS/certificate related text in version -11 
was *really*...err... unclear, so I think we need to rewrite
it to some extent before taking it to the WG list (fortunately, 
the whole text is only two pages, so this shouldn't be
too much effort). We also have an option (fingerprints)
that wasn't present before, so we need to recheck the WG 
consensus anyway.

Some proposed text fragments from me (Joe, please feel free 
to edit as you like):

4.2

   TLS typically uses certificates to authenticate
   peers. Authentication and authorization of the TLS server
   (transport receiver) is described in Section 4.2.1; authentication
   and authorization of the TLS client (transport sender) is described
   in Section 4.2.2.

4.2.1 Server authentication/authorization

   The transport sender (TLS client) has three different options for
   authenticating and authorizing the transport receiver (TLS server):

   (Pasi's note: it could be sufficient is one of the following
   two is a MUST, and the other one is a SHOULD.)

   o  Certification path validation and subject name verification: the

      client is configured with one or more trust anchors, and for 
      each transport receiver, the name to be matched against the  
      certificate. This option MUST be supported.

   o  Certificate fingerprints: For each transport receiver, the
client 
      is configured with a fingerprint of the server's certificate
      (which can be self-signed). This option MUST be supported.

   o  No server authentication/authorization: The client is configured

      to accept any certificate from the server. This option
      MAY be supported, but MUST NOT be enabled by default.

   For certification path validation, client implementations MUST
   provide a mechanism for configuring one or more trust anchors, and
   MUST perform certification path validation as specified in
   [RFC3280bis].
 
   For subject name verification, client implementations MUST support
   configuring, for each transport receiver, the name to be matched
   against the certificate.  This name may be the host name or IP
   address used when opening the TCP connection, or a distinct host
   name (...details of name matching...MUST support DNS names,
   probably others can be MAY...)

   To support certificate fingerprints, client implementations MUST
   support configuring, for each transport receiver, a fingerprint of
   the server certificate. See Section 4.2.3 for details.

   If server authentication/authorization fails, the client SHOULD log
   the error in some form or another (...more text...)

4.2.2 Client authentication/authorization
  
   The transport receiver (TLS server) has three different options for
   authenticating and authorizing the transport sender (TLS client).

   (Pasi's note: it could be sufficient is one of the following
   two is a MUST, and the other one is a SHOULD.)

   o  Certification path validation and subject name verification:
      the server is configured with one or more trust anchors,
      and a set of names (or wildcard patterns) to be matched 
      against the certificates.  This option MUST be supported.

   o  Certificate fingerprints: The server is configured with the 
      fingerprints of client certificates. This option MUST be
      supported.

   o  No client authentication/authorization (or authorization
      based only on connection source IP address): This option MAY 
      be supported, but MUST NOT be enabled by default.

   Certification path validation and subject name verification work
   as described in Section 4.2.1 above, with following addition: 
   (...locally configured client name can be a wildcard; different 
   from wildcard-in-cert case...)

   To support certificate fingerprints, server implementations MUST
   support configuring with a list of fingerprints of authorized
   certificates. See Section 4.2.3 cor details.

4.2.3 Certificate fingerprints

   Both client and server implementations MUST make the certificate
   fingerprint available through a management interface. If no other
   certificate is configured, both client and server implementations
   MUST support generating a key pair and self-signed certificate.

   <describe details of certificate fingerprint calculation here. 
   this should be compatible with the way e.g. current web browsers
   calculate fingerprints> "

and after Joe did some additioon revising, Pasi said:
"I'd be interested in getting the WG's opinion on this (in
particular, the fingerprint stuff) as soon as possible."

At this point, Joe revised and published the draft and we brought it
to the WG for comment.

Hope this helps


David Harrington
[e-mail]
[e-mail]
[e-mail]

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