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Messaging Interoperability and Client Security

Eric Rescorla has a thoughtful and nuanced assessment of recent EU proposals which would compel messaging companies to make their communications services interoperable. To his immense credit he spends time walking the reader through historical and contemporary messaging systems in order to assess the security issues prospectively associated with requiring interoperability. It’s a very good, and compact, read on a dense and challenging subject.

I must admit, however, that I’m unconvinced that demanding interoperability will have only minimal security implications. While much of the expert commentary has focused on whether end-to-end encryption would be compromised I think that too little time has been spent considering the client-end side of interoperable communications. So if we assume it’s possible to facilitate end-to-end communications across messaging companies and focus just on clients receiving/sending communications, what are some risks?1

As it stands, today, the dominant messaging companies have large and professional security teams. While none of these teams are perfect, as shown by the success of cyber mercenary companies such as NSO group et al, they are robust and constantly working to improve the security of their products. The attacks used by groups such as NSO, Hacking Team, Candiru, FinFisher, and such have not tended to rely on breaking encryption. Rather, they have sought vulnerabilities in client devices. Due to sandboxing and contemporary OS security practices this has regularly meant successfully targeting a messaging application and, subsequently, expanding a foothold on the device more generally.

In order for interoperability to ‘work’ properly there will need to be a number of preconditions. As noted in Rescorla’s post, this may include checking what functions an interoperable client possesses to determine whether ‘standard’ or ‘enriched’ client services are available. Moreover, APIs will need to be (relatively) stable or rely on a standardized protocol to facilitate interoperability. Finally, while spam messages are annoying on messaging applications today, they may become even more commonplace where interoperability is required and service providers cannot use their current processes to filter/quality check messages transiting their infrastructure.

What do all the aforementioned elements mean for client security?

  1. Checking for client functionality may reveal whether a targeted client possesses known vulnerabilities, either generally (following a patch update) or just to the exploit vendor (where they know of a vulnerability and are actively exploiting it). Where spam filtering is not great exploit vendors can use spam messaging as reconnaissance messaging with the service provider, client vendor, or client applications not necessarily being aware of the threat activity.
  2. When or if there is a significant need to rework how keying operates, or surveillance of identity properties more broadly that are linked to an API, then there is a risk that implementation of updates may be delayed until the revisions have had time to be adopted by clients. While this might be great for competition vis-a-vis interoperability it will, also, have the effect of signalling an oncoming change to threat actors who may accelerate activities to get footholds on devices or may warn these actors that they, too, need to update their tactics, techniques, and procedures (TTPs).
  3. As a more general point, threat actors might work to develop and propagate interoperable clients that they have, already, compromised–we’ve previously seen nation-state actors do so and there’s no reason to expect this behaviour to stop in a world of interoperable clients. Alternately, threat actors might try and convince targets to move to ‘better’ clients that contain known vulnerabilities but which are developed and made available by legitimate vendors. Whereas, today, an exploit developer must target specific messaging systems that deliver that systems’ messages, a future world of interoperable messaging will likely expand the clients that threat actors can seek to exploit.

One of the severe dangers and challenges facing the current internet regulation landscape has been that a large volume of new actors have entered the various overlapping policy fields. For a long time there’s not been that many of us and anyone who’s been around for 10-15 years tends to be suitably multidisciplinary that they think about how activities in policy domain X might/will have consequences for domains Y and Z. The new raft of politicians and their policy advisors, in contrast, often lack this broad awareness. The result is that proposals are being advanced around the world by ostensibly well-meaning individuals and groups to address issues associated with online harms, speech, CSAM, competition, and security. However, these same parties often lack awareness of how the solutions meant to solve their favoured policy problems will have effects on neighbouring policy issues. And, where they are aware, they often don’t care because that’s someone else’s policy domain.

It’s good to see more people participating and more inclusive policy making processes. And seeing actual political action on many issue areas after 10 years of people debating how to move forward is exciting. But too much of that action runs counter to the thoughtful warnings and need for caution that longer-term policy experts have been raising for over a decade.

We are almost certainly moving towards a ‘new Internet’. It remains in question, however, whether this ‘new Internet’ will see resolutions to longstanding challenges or if, instead, the rush to regulate will change the landscape by finally bringing to life the threats that long-term policy wonks have been working to forestall or prevent for much of their working lives. To date, I remain increasingly concerned that we will experience the latter than witness the former.


  1. For the record, I currently remain unconvinced it is possible to implement end-to-end encryption across platforms generally. ↩︎

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