Summarizing Known Attacks on Transport Layer Security (TLS) and Datagram TLS (DTLS)
draft-ietf-uta-tls-attacks-05

[Ballot comment]
It might be useful to note that SSL stripping is a flavor of downgrade attack.  Likewise, it could be worth noting in this section or Section 2.2 that STARTTLS is very vulnerable to downgrade without some sort of HSTS-like mechanism.  For example, there's some recent evidence of downgrade attacks on mail protocols. 

Downgrade in general could use more attention.  The IETF can fix things in newer versions of the protocol, but if the client and server can't negotiate that version, it's all for naught.

https://www.techdirt.com/blog/netneutrality/articles/20141012/06344928801/revealed-isps-already-violating-net-neutrality-to-block-encryption-make-everyone-less-safe-online.shtml

Given the news about POODLE this week, I would suggest changing Section 2.4 to be "Padding Oracle Attacks", and adding POODLE there.

I'm surprised not to see some mention of Heartbleed in Section 2.13.

[Ballot comment]
A tiny thing in the Introduction: "suffice it to say" may sound cute, but if it were really sufficient, the document could stop there.  I suggest replacing "suffice it to say" with "a quick summary is".  But take this or leave it as you please.

My other comment is more significant:

-- Section 2.13 --

  o  Implementations may not validate the server identity.  This
      validation typically amounts to matching the protocol-level server
      name with the certificate's Subject Alternative Name field.  Note:
      historically, although incorrect, this information is also often
      found in the Common Name part of the Distinguished Name instead.

I had to read the "note" a few times before I followed it.  It's not the information that's incorrect, and the "also ... instead" bit is confusing.  But the biggest problem is that it's unclear what the incorrect thing IS: is it that the information is put in the CN and shouldn't be?  Or is it that validators retrieve it from there instead of from the SAN?  Maybe this (correct it as necessary)?:

NEW
  o  Implementations might not validate the server identity.  This
      validation typically amounts to matching the protocol-level server
      name with the certificate's Subject Alternative Name field.  Note:
      this same information is often in the Common Name part of the
      Distinguished Name also, and some validators incorrectly retrieve
      it from there instead of from the Subject Alternative Name.

(That also changes the "may" to "might", to avoid accidentally conveying a sense of permission.)

[Ballot discuss]
Thank you for your work on this draft!  It looks great, but I do have two items I'd like to discuss and see if we can add text to address these concerns/attacks before switching to a yes. 

1. I think it would be very helpful to include what techniques are used by forensic tools that enable access to decrypt TLS sessions and how to respond/prevent that access.  I see you have certificate attacks listed in 2.7, which is what the common forensic tools leverage.  However, these tools also require access to the private key, and it would be helpful to mention the importance of protecting the private key, preventing exportability, etc.. 

In 2.7 I thin it would be helpful to explicitly state that commonly used forensic tools such as wireshark require access to the private key as well as use of RSA.  Another option might be to add the recommendation to protect the private key in 2.13.  If you can't export the key (from an implementation perspective), that could go a long way to helping to reduce this method of exposure.

I've included a few links for additional information on the list of tools and explicit details of the attack used in case this is helpful.
  Forensic tools that rely on a MiTM attack to decrypt TLS and DTLS session:
    http://forensicswiki.org/wiki/SSL_forensics
  Wireshark requires you have the key: http://support.citrix.com/article/CTX116557
  Mitigations are to protect the private key and to not use RSA:
    http://wirewatcher.wordpress.com/2010/07/20/decrypting-ssl-traffic-with-wireshark-and-ways-to-prevent-it/
    http://wiki.wireshark.org/DTLS?highlight=%28tls%29

If you would like text suggestions, let me know and I'll help.

2. I realize this draft covers explicit attacks against TLS, however since pervasive monitoring is considered an attack, it could be helpful for this draft also cover techniques used by middle boxes to intercept TLS streams (proxy firewalls, load balancers, etc.).  Although these are more of 'attacks' on the user, than of TLS, it could be a short addition to have this documented. 

The TLS session is intercepted, or in the case of a load balancer it might be terminated, with a second TLS session initiated to the destination allowing traffic to pass in the clear on the middlebox.  The user is alerted and warned to accept an untrusted certificate in this process, and many do as a result of corporate restrictions (they have no choice if they want to go to that site). 

Perhaps implementation recommendations could assist here to improve the warnings to the user, letting them know their traffic may be passing in the clear and they may not want to continue with their session.  Some may chose to avoid certain transactions from the work place as a result.


If you have already discussed these items and decided they were out of scope, please let me know.  I support this work and just wanted to make sure we covered all bases or put some out of scope.  Thank you.

[Ballot comment]

I have a number of nits. Please treat them as such.

- Is "current" correct in the name for an RFC? Perhaps
"known" is better.

- intro, para 2: s/is tasked/was tasked/

- s2, 2nd para: "a more systemic solution" is left hanging
- do you mean TLS1.3? If so, maybe say so?

- 2.5, 2nd para: draft-ietf-tls-prohibiting-rc4 does not
itself provide those details, maybe say "see the
references in" that draft?

- 2.6: should the RFC editor wait on the official
allocation of the BEAST CVE number? I don't think that's
happened already has it?

- 2.7, is Bleichenbacher really a certificate attack?  I
think its not, but is a pkcs#1 encryption attack.  (It
would apply just as well to OOB keys in TLS.) I'm not sure
if Klima is or is not the same in that respect.  Also the
timing attacks in the 2nd para, don't seem to be
certificate related are they? So perhaps only the last
para is really certificate related?

- 2.8: I forget if this has been discussed - should three
be a reference to draft-ietf-tls-negotiated-ff-dhe

- 2.10: isn't TRIPLE-HS published yet?

- 2.12: A reference would be good here if we have one,
esp. for the "It is known" point.

- 2.13, para1: "fully specified" isn't really correct
there, I think you mean 'properly specified, so that
implementations should be "secure"' but maybe some other
wording would be better.

- 2.13: Doesn't that paper also blame hard-to-use APIs as
well as the IETF protocols and their complexity? Worth a
mention?

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-uta-tls-attacks-04, which is currently in Last Call, and has the following comments:

We understand that this document doesn't require any IANA actions.

While it is helpful for the IANA Considerations section of the document to remain in place upon publication, if the authors prefer to remove it, IANA doesn't object.

If this assessment is not accurate, please respond as soon as possible.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Sender:
Subject: Last Call:  (Summarizing Current Attacks on TLS and DTLS) to Informational RFC


The IESG has received a request from the Using TLS in Applications WG
(uta) to consider the following document:
- 'Summarizing Current Attacks on TLS and DTLS'
  as Informational RFC

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2014-10-13. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  Over the last few years there have been several serious attacks on
  TLS, including attacks on its most commonly used ciphers and modes of
  operation.  This document summarizes these attacks, with the goal of
  motivating generic and protocol-specific recommendations on the usage
  of TLS and DTLS.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-uta-tls-attacks/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-uta-tls-attacks/ballot/


No IPR declarations have been submitted directly on this I-D.

1. Summary

Leif Johansson is the shepherd.
Pete Resnick is the responsible AD

The shepeard believs the document is ready to go.

Abstract
-----------
Over the last few years there have been several serious attacks on
TLS, including attacks on its most commonly used ciphers and modes of
operation.  This document summarizes these attacks, with the goal of
motivating generic and protocol-specific recommendations on the usage
of TLS and DTLS.
-----------

The document is intended for publication as an Informational RFC

2. Review and Consensus

The document has received extensive review on the uta list by several
reviewers (not just the usual suspects). There have been a few near-miss
consensus, but they were all resolved to the satisfaction of all involved.

Most of the reviewers / active participants have ties to information
security or TLS specifically. Additional review in the secdir group
should probably try to find a person with another perspective.

3. Intellectual Property

No issues

4. Other points

The ID nits page lists an obsoleted reference RFC 4347 (Obsoleted by
RFC 6347) but that can probably be delt with as an RFC editors note.

There are no IANA considerations.