Category Archives: Standards

PKI Challenges and Gaps for Federation

I recently interviewed XMPP co-chair Joe Hildebrand for regarding XMPP Domain Name Assertions (DNA) used to enable certain instant messaging federation use cases where an XMPP server might host multiple domains. Without DNA, it’s effectively impossible to use TLS for these multiple-domain scenarios, but that’s not the main point of this post. During the course of our conversation, we touched on the general problem of how you leverage PKI and digital certificates to establish trust between two domains for a given application protocol (itself a well-understood concept in theory) and the practical challenges that still remain on a protocol-by-protocol basis for ensuring integrity when binding a certificate to a domain for a given protocol.

Take SIP-TLS for example. We’ve run into more than a few implementations that check for a valid certificate but do absolutely no validation of the domain itself, such that if I send a message purporting to be from after presenting a valid certificate from, not even so much as an error message is logged. Moreover, SIP doesn’t actually specify how such validation should take place, leading to vendor-proprietary implementations that utilize different certificate subject mechanisms and complicate SIP federation.

I noticed a few comments on my prior post claim that UC federation is effectively a solved problem. That’s only true if you narrow the meaning of UC federation to an absurdly small subset of the communications and collaboration space. Yes, XMPP federation for simple domain pairs for instant messaging is well defined with many interoperable vendor implementations today. Frankly, XMPP federation is the best story we’ve got for federation in the UC space, as the story degrades quickly from there. The next-best stories are effectively vendor-specific with Microsoft OCS Federation and Cisco’s Intercompany Media Engine (currently the only product using ViPR – (Verification involving PSTN Reachability – an IETF draft standard proposed by Cisco). There’s a lot of work left to do before all communications and collaboration services are federateable between enterprises, and it turns out that these certificate binding problems are one of the big gaps. To date, XMPP is the closest to solving them and the IETF is considering adopting general standards for protocol certificate binding based on related work – see: draft-saintandre-tls-server-id-check-02 for example]

There’s more to come on this topic in the near future, but for now I just want to leave you with this: it doesn’t matter how secure an established TLS connection is for a given protocol if you can’t bind application-layer domain claims with the certificate used for TLS session establishment. It’s a common fallacy that TLS “makes you secure” all by itself – that’s akin to saying that seat belts and airbags will prevent you from crashing. Federation can only succeed when all associated protocols have well-understood certificate and domain bindings that are properly validated by vendor products used by the federation participants. Anyone who tells you that’s a solved problem today for UC is delusional.

W3C Voice Biometrics workshop coming up in March

Through a colleague of mine, Dan Burnett, I just learned about an upcoming W3C Biometrics workshop in March in California around the subject of “Speaker Identification and Verification (SIV)”. As Dan writes:

To get more information from the knowledgeable public, W3C is holding a workshop to “identify and prioritize directions for SIV standards work as a means of making SIV more useful in current and emerging markets. ” The workshop will be held in early March at SRI in Menlo Park, California.

Although the paper submission deadline has passed, if you were unaware of this workshop and are dying to attend, please email as described in the Call for Participation.

More information can also be found on the W3C Biometrics Workshop site. Sounds like an interesting conference to attend… (Dan Burnett will be there, but I will not).

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5th Emergency Services Workshop to be held Oct 21-23 in Vienna

How does an emergency call to 9-1-1 or 1-1-2 (or whatever your local emergency number may be) work in a world of voice-over-IP?

It’s not a topic we cover hardly at all here on this blog, yet it’s definitely one of the security and social/cultural aspects of our migration to IP that we definitely have to get right. If we as an industry don’t, people can die. (Or the migration to VoIP will be significantly delayed.)

To that end, a number of emergency services experts are meeting to discuss ongoing work on IP-based emergency services in Vienna, Austria on 21st to 23rd October 2008. The first workshop day is focusing on tutorials to help those interested in the classical 1-1-2 (or 9-1-1) emergency call to get up-to-speed with architectures and standards developed for next generation emergency calling. During the second day various recent activities of standardization organizations around the world will be presented. The third workshop day is dedicated to early warning standardization efforts and the outlook to future emergency services activities.

Participation from those working in standardization organizations as well as persons with interest into the subject is highly appreciated. The event is open to the public and anyone may attend.
For socializing an evening program has been organized. There is a nominal fee of 120 Euros charged to cover the facilities cost, food, drinks, etc. Arrangements are also being made for participants to join remotely.

More information about the workshop can be found behind the following link:

This page also points to previous workshops that took place in New York, Washington, Brussels and Atlanta.

(Thanks to Hannes Tschofenig for providing the majority of this text.)

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US government rolling out largest DNSSEC deployment

It’s not “VoIP security”-related, but this piece in NetworkWorld today is worth a read: “Feds tighten security on .gov“. Here’s the intro:

When you file your taxes online, you want to be sure that the Web site you visit — — is operated by the Internal Revenue Service and not a scam artist. By the end of next year, you can be confident that every U.S. government Web page is being served up by the appropriate agency.

That’s because the feds have launched the largest-ever rollout of a new authentication mechanism for the Internet’s DNS. All federal agencies are deploying DNS Security Extensions (DNSSEC) on the .gov top-level domain, and some expect that once that rollout is complete, banks and other businesses might be encouraged to follow suit for their sites.

The article goes on at some length into what the US government is doing, the issues involved and why it all matters. From a larger “Internet infrastructure” point-of-view, actions such as securing the DNS infrastructure will only help in securing services such as VoIP. There’s still a long way to go to getting DNSSEC widely available, but I applaud the US government for helping push efforts along.

FYI, the article references the obsolete RFC 2065 for DNSSEC. For those wishing the read the standard itself, DNSSEC is now defined in RFC’s 4033, 4034 and 4035 with a bit of an update in RFC 4470.

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Variable Bitrate Compression Flawed

Some researchers over at Johns Hopkins University have discovered that due to the way Variable Bitrate Compression does it’s thing, even if the audio stream is encrypted it is still possible to determine entire words and phrases based on the lengths of the packets with a high degree of accuracy.

According to the article referenced above it appears that the proof of concept tool is fairly limited, but given a little time and additional effort it’s capabilities could be greatly expanded, potentially to the point of transcribing entire conversations.

The researchers’ paper was presented at the 2008 IEEE Symposium on Security and Privacy a few weeks ago.

Web page for RUCUS BOF at IETF 71 now at new URL

ietflogo-1.jpgAs I mentioned previously (here and here), the “RUCUS” BOF about voice spam at IETF 71 in Philadelphia is one of great interest with its focus on voice spam, a.k.a. “SPam for Internet Telephony” or “SPIT”. Unfortunately BOF co-chair Hannes Tschofenig ran into a problem with his domain and had to move the page to a new URL:

If you saved the URL or sent it on to someone, you’ll need to update to using the new URL. If you didn’t visit the RUCUS page before, please do check it out – and feel free to join the RUCUS mailing list. Of course, if you can, please do join us in person in Philadelphia!

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Slides about Peer-to-peer SIP (P2PSIP) security now available

ietflogo-1.jpgWant to learn more about the voip security aspects of peer-to-peer SIP? As I mentioned in the VOIPSEC mailing list last week, researchers from Huawei and the University of California recently released an Internet-Draft called “P2PSIP Security Analysis and Evaluation” which dives into an analysis of security issues in P2PSIP. It’s a good overview and one I’d strongly recommend to folks. (Note – you may want to read “P2PSIP Concepts” first to understand the language being used.)

Beyond the Internet-Draft, though, the researchers announced yesterday that their slides are now available (PPT) that go into the issues. These are being prepared from presentation at the upcoming IETF 71 meeting March 10-14 in Philadelphia, so if you are attending the event you’ll be able to hear the presentation yourself.

Peer-to-peer SIP is a fascinating area of current research and it’s good to see work like this being put into exploring the security aspects. Note – the researchers are looking for feedback so if you have comments on what you read, their contact information is in the Internet-Draft.

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Join the new RUCUS mailing list if you want to look at ways to end SPIT!

ietflogo.jpgAs mentioned previously, there is a new session planned for IETF 71 in March called “Reducing Unwanted Communications Using SIP“, a.k.a. “RUCUS”.

The RUCUS mailing list is now open for subscriptions and we encourage anyone interested in looking at how we address the issue of voice spam, aka “Spam for Internet Telephony” aka “SPIT” to join into the conversation.

We would ask you to please read the group description prior to joining so that you understand what we are trying to do. The primary goal of this session in March in Philadelphia is to look to understand the architecture necessary to address the issue and identify the pieces of that architecture that may already be there or may need to be put in place.

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End-to-end VoIP security using DTLS-SRTP? (A new proposal…)

ietflogo.jpgAs we’ve discussed both here and on Blue Box, the issue of securing the keys for Secure RTP is one of the remaining challenges to have secure voice transmission in the open standards world of SIP. Out of the large number of proposals to secure the key exchange, “DTLS” emerged as the choice of the IETF… but it still had the issue that an endpoint needed to be sure of the authenticity of the other endpoint’s certificate. SIP Identity (RFC 4474) and a draft “Identity-Media” from Dan Wing addressed the authenticity issue but broke in some common network configurations. Now Kai Fisher has put out an Internet Draft called “End-to-End Security for DTLS-SRTP” that proposes a mechanism to address that. In the post to the SIP mailing list, Kai explains the motivation:

I have submitted a draft proposing a solution to secure a DTLS-SRTP handshake and hence SRTP end-to-end (in terms of end-domain to end-domain). As discussed during the last IETF meetings and analyzed by Dan’s Identity-Media draft, current solutions like SIP Identity do not protect the authenticity of the fingerprint end-to-end in certain inter-domain scenarios. For example, a modification of SDP m-/c-lines or the From header field by intermediaries breaks the SIP-Identity or Identity-Media signature and causes a re-signing by a domain different to the originating one. The draft proposes a solution for such scenarios without the need to re-sign during domain traversal and which preserves the original identity information.

The abstract to the draft provides more info:

The end-to-end security properties of DTLS-SRTP depend on the authenticity of the certificate fingerprint exchanged in the signalling channel. In current approaches the authenticity is protected by SIP-Identity or SIP-Identity-Media. These types of signatures are broken if intermediaries like Session Border Controllers in other domains change specific information of the SIP header or the SIP body. The end-to-end security property between the originating and terminating domain is lost if these intermediaries re-sign the SIP message and create a new identity signature using their own domain credentials.

This document defines a new signature type ‘Fingerprint-Identity’ which is exchanged in the signalling channel. Fingerprint-Identity covers only those elements of a SIP message necessary to authenticate the certificate fingerprint and to secure media end-to-end. It is independent from SIP-Identity and SIP-Identity-Media and can be applied in parallel to them.

More details can, of course, be found in the draft. As noted in the post to the SIP mailing list, Kai is looking for feedback. This is an important issue to get done – and to get done correctly – so we strongly urge people to take a look at the document and provide feedback if you see ways the proposal can be improved.

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Raising a RUCUS about SPIT at IETF 71!

UPDATE: The RUCUS mailing list is now open for subscription.

ietflogo.jpgWant to get together with others and discuss in further detail what we can do about Spam for Internet Telephony (SPIT)? A new session has been approved for the IETF 71 meeting coming up in Philadelphia in March called “Reducing Unwanted Communications using SIP” a.k.a. “RUCUS” (Hey, it’s not a real IETF group until it has a cute acronym!) Hannes Tschofenig, who submitted the proposal, has created a RUCUS web page and is looking for feedback. The page says in part:

The topic of dealing with unwanted traffic in SIP has surfaced several times in the IETF in the context of preventing Spam for Internet telephony. Previous attempts to have a structured discussion about this topic have (among other reasons) failed due to the strong focus on selected solution approaches.

Prior work in SIP on identity management has an important role in this activity since a strong identity mechanism in SIP has been seen as a prerequisity for establishing authorization policies. Hence, the “Discussion and Analysis of SIP Identity” (DASI) BoF is relevant for this event. Even though there is no direct dependency between the two activities the number of interested participants will quite likely overlap.

This BoF focuses on the discussion of architectural aspects. The underlying theme is that the work on building blocks is more fruitful once the larger framework is understood. A number of solutions components have been submitted to the IETF, have been published in the academic literature and found their way into other standardization bodies. Reduce unwanted communication requires authorization decisions to be made. These decisions can be made based on individual sessions but also on the interaction at a higher granularity (e.g., the interaction with a specific VoIP provider network). Examples of questions with relevance for an architecture might be:
– Where does information for decision making come from?
– What are useful information items for decision making?
– Where are policy decision points located? What about the placement of
policy enforcement points?
– Are privacy aspects to consider with the exchange of information?
– How does the underlying trust model look like?
– What assumptions are certain mechanisms based on?
– Can individual proposals be combined in a reasonable way?

It is not the aim of the BoF to discuss specific solution approaches since it is likely that multiple techniques have to be used in concert.

If you are attending IETF 71 in Philadelphia in March, do plan on joining in the RUCUS! (I’ll be there.)

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