The UK government's official voice encryption protocol, around which it is hoping to build an ecosystem of products, has a massive backdoor that would enable the security services to intercept and listen to all past and present calls, a researcher has discovered.

Dr Steven Murdoch of University College London has posted an extensive blog post digging into the MIKEY-SAKKE spec in which he concludes that it has been specifically designed to "allow undetectable and unauditable mass surveillance."

He notes that in the "vast majority of cases" the protocol would be "actively harmful for security."

Murdoch uses the EFF's scorecard as a way of measuring the security of MIKEY-SAKKE, and concludes that it only manages to meet one of the four key elements for protocol design, namely that it provides end-to-end encryption.

However, due to the way that the system creates and shares encryption keys, the design would enable a telecom provider to insert themselves as a man-in-the-middle without users at either end being aware. The system would also allow a third party to unencrypt past and future conversations. And it does not allow for people to be anonymous or to verify the identity of the person they are talking to.

In other words, it would be the perfect model for the security services, who can apply pressure to a telecom company and then carry out complete surveillance on an unidentified individual.

While it is surprising that the official UK government system would have such a significant backdoor, it is perhaps less surprising when you consider who developed the spec: the information security arm of the UK listening post GCHQ, the Communications-Electronics Security Group (CESG).

The CESG – and the UK's civil service – started pushing the approach late last year and has incorporated it into a product spec called Secure Chorus. It has also set itself up as an evaluator of other products and is trying to market its approach commercially by pushing it as "government-grade security." One example of a product already going through this evaluation is Cryptify Call, available for iOS and Android.

Guess which one was developed by the UK security services

There is increasing demand for voicecall encryption. Unlike instant messaging, which effectively allowed companies to start from scratch and so has resulted in a number of highly secure products, phonecalls run over older infrastructure and almost always pass through telecom companies, usually in an unencrypted form (although the information may be encrypted while in transit).

MIKEY-SAKKE is unusual in that unlike most secure messaging and phone systems, it makes no effort at all to protect the identity of the people communicating with one another, providing easy-to-access maps of metadata.

That metadata can be used to specifically identify individuals and then, using the backdoor, access all their calls past and present. In other words, it is the perfect spying system.

Murdoch highlights in his post a number of occasions in which the UK security services have successfully compromised mobile phone networks – instances that were revealed by Edward Snowden – and notes that this is likely only the tip of the iceberg.

If at first you don't succeed

He also notes that GCHQ tried 20 years ago to introduce a similar protocol but that a "notable difference" exists between that effort and this MIKEY-SAKKE approach: "While the GCHQ protocol was explicitly stated to support key escrow to facilitate law enforcement and intelligence agency access, this controversial aspect has not been included in the description of MIKEY-SAKKE and instead the efficiency over EDH is emphasised."

Or in other words, the UK government doesn't want you to know that it can spy on everything you say.

Murdoch notes that things don't have to be this way – there are other products and protocols that provide a much higher level of security. Some, for example, protect past messages from being unencrypted, so even if someone does gain access to your encryption keys, they are limited to current calls. Others make it much harder for telcos to access unencrypted data as it flows through their system.

The hardest aspect, however, is ensuring that when initial contact is made with someone in order to exchange key encryption information, there isn't a person in the middle. One system to do this is to have people physically read out two words that appear on a device and have the other person hear and verify them before starting an encrypted conversation. However, Murdoch notes that even this approach is not foolproof; an attacker could simply impersonate the other caller.

In short then, unless you want to give telcos and government agencies unrestricted access to your phonecalls, it's best not to buy into the MIKEY-SAKKE / Secure Chorus claims of security. ®