IDNA flaws with regard to U+2024

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In a bug report against libidn, Erik van der Poel gives an example of an internationalized domain name that is handled differently by different implementation. Another example of one such string is:

‘räksmörgÃ¥s’ U+2024 ‘com’

If your browser supports Unicode, the string is: räksmörgÃ¥s․com. Use cut’n’paste of the string into your browser and see what it tries to lookup (please let me know what you notice!).

The problem with this string is that it is on the form “[non-ASCII][DOT-Like code point]com”. Here ‘räksmörgÃ¥s’ represents the non-ASCII string, which can be any non-ASCII string. Further, the U+2024 represent one character which looks like a dot, there are others that also contain dot-like characters.

The IDNA algorithm (section 3.1) implies that applications should treat the string as one label. The U+2024 character is not one of the dot-like characters that needs to be treated as a label separator. The ASCII string which is output after applying the IDNA algorithm is:

xn--rksmrgs.com-l8as9u

Note that the string contains an ASCII dot ‘.’ (0x0E). If applications are not careful how they resolv the name in the DNS, they will request information in a non-existing top-level domain ‘com-l8as9u’. This is because the DNS do not use ‘.’ to separate labels, but instead uses a length-value pair for each label. Thus the wrong string to lookup would be:

(11)xn--rksmrgs(10)com-l8as9u

Whereas the right string to lookup would be:

(22)xn--rksmrgs.com-l8as9u

Using DNS master file syntax, the name to lookup is xn--rksmrgs.com-l8as9u.

What’s interesting here is that some implementations, such as Microsoft Internet Explorer and Firefox implements IDNA not according to the standard. Instead, they compute the following string:

xn--rksmrgs-5wao1o.com

Arguable, this is a better approach than what is specified by RFC 3490. MSIE/Firefox recognize that U+2024 is a “dot-like” character, by using NFKC. What is debatable is whether U+2024 will actually occur in practice, Unicode expert Kenneth Whistler says U+2024 will not be entered accidentally.

As the maintainer of GNU Libidn, I’m not yet sure about what to do about the situation. The conservative approach is to do nothing until the RFCs are updated. I have come up with a patch to add a new IDNA flag that treat U+2024 as a dot-like character early on. This would at least make it possible to produce the same (RFC non-conforming) output that MSIE/Firefox computes.

PAM module for Yubico

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During the autumn, in Yubico, we have been working on a PAM module for the Yubikey. It allows you to use the Yubikey to login to your machine, to unlock the screensaver, and so on. I decided to let Google Code host this project, which is the first time I’ve used them. It will be interesting to see how working with their site is going to turn out.

ObLink: code.google.com/p/yubico-pam/

You can buy Yubikeys on our web shop. If you have an interesting idea about what can be done with the key, let me know and I may be able to arrange a good deal for you. 🙂

Response to GnuTLS in Exim Debate

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Marc Haber blogs about GnuTLS in Exim4, and it suggests there is a long list of technical issues in GnuTLS. Given my involvement in GnuTLS, I decided to analyze each bug to see what we can learn and possibly improve.

I looked at the all bugs tagged with gnutls in the exim4 bug tracker. My impression is that Marc Haber has done a very good job as Exim4 maintainer in dealing with these GnuTLS related problems. Some of the frustration seems to be because submitters don’t respond to questions. Also it seems different problems are discussed at the same time, which makes it very difficult to help isolate and solve the problem. The only serious problem I’ve identified is the entropy depletion problem, and the GnuTLS team will try to address it. To me, the concern seems more of a volunteer time issue than a technical one.

Quick Summary

Bug #348046 is so complex that I cannot judge it. If the submitters are willing, it may be best to re-submit each problem separately. The problem with TheBat is interesting, but given the non-free status of TheBat and no other reports, it doesn’t seem serious. To reduce entropy consumption is something we should work on, but it is a ‘wishlist’ kind of bug, and to some extent may have already been solved by removing the DH generation code which depleats the entropy pool quickly. The rest appears to be already solved or should be tagged as ‘wontfix’.
Continue reading Response to GnuTLS in Exim Debate→

FSCONS

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A free software conference in Sweden? That’s a rare one. Organized by the FSFE and Henrik Sandklef, it will be held on the 7-8 December 2007. I hope we’ll see more of this in Sweden. I’m proud to have been invited to talk about both GnuTLS and OpenID. I’m happy to see that there is a OpenMoko talk as well. If you want to participate, there is an early bird discount if you register now. If someone is going and would like to chat, drop me an email.

On TLS-AUTHZ

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The TLS-AUTHZ document (protocol spec here) describes a mechanism to add support for authorization in the TLS protocol. The idea is part of a patent application, see the patent notification to the IETF. The protocol has a complicated history in the IETF. Right now a third last call is open to request feedback from the community. I’ve written about TLS-AUTHZ before.

RedPhoneSecurity is now trying to circumvent the IETF standardization process by trying to get the document published as an ‘experimental standard’. The document earlier failed to get consensus for publication on the standards track.

The responsible IETF Area Director, Tim Polk, argues that because there exists independent implementations, the community benefits from having the document published. The argument is silly because the only independent implementation is mine and I’m opposed to publication of the standard. Further, the document will remain accessible to anyone in the community with access to the Internet since it has been published as an Internet Draft. To clarify that we have no interest in a standard with patent claims, we have decided to remove the tls-authz implementation from GnuTLS. Together with the FSF we came up with the following statement which is part of the GnuTLS 2.0.2 release announcement:

** TLS authorization support removed.
This technique may be patented in the future, and it is not of crucial importance for the Internet community. After deliberation we have concluded that the best thing we can do in this situation is to encourage society not to adopt this technique. We have decided to lead the way with our own actions.

If you are concerned about having patented standards adopted by the IETF, now is a very good time to make your voice heard! The last call ends on October 23th. Please read about the issue, and familiarize yourself with the IETF process (RFC 2026, with updates related to patents in RFC 3989) and send your feedback to ietf@ietf.org.