-------- Forwarded Message -------- Subject: [Cryptography] GCHQ's plan to backdoor encrypted phone calls Date: Tue, 19 Jan 2016 19:03:25 -0800 From: Henry Baker To: cryptography@metzdowd.com FYI -- The whole article is too long to reproduce here; follow the link to read the whole article. https://www.benthamsgaze.org/2016/01/19/insecure-by-design-protocols-for-enc... Insecure by design: protocols for encrypted phone calls The MIKEY-SAKKE protocol is being promoted by the UK government as a better way to secure phone calls. The reality is that MIKEY-SAKKE is designed to offer minimal security while allowing undetectable mass surveillance, through the introduction a backdoor based around mandatory key-escrow. This weakness has implications which go further than just the security of phone calls. The current state of security for phone calls leaves a lot to be desired. Land-line calls are almost entirely unencrypted, and cellphone calls are also unencrypted except for the radio link between the handset and the phone network. While the latest cryptography standards for cellphones (3G and 4G) are reasonably strong it is possible to force a phone to fall back to older standards with easy-to-break cryptography, if any. The vast majority of phones will not reveal to their user whether such an attack is under way. The only reason that eavesdropping on land-line calls is not commonplace is that getting access to the closed phone networks is not as easy compared to the more open Internet, and cellphone cryptography designers relied on the equipment necessary to intercept the radio link being only affordable by well-funded government intelligence agencies, and not by criminals or for corporate espionage. That might have been true in the past but it certainly no longer the case with the necessary equipment now available for $1,500. Governments, companies and individuals are increasingly looking for better security. A second driver for better phone call encryption is the convergence of Internet and phone networks. The LTE (Long-Term Evolution) 4G cellphone standard carries voice calls over IP packets, and desktop phones in companies are increasingly carrying voice over IP (VoIP) too. Because voice calls may travel over the Internet, whatever security was offered by the closed phone networks is gone and so other security mechanisms are needed. Like Internet data encryption, voice encryption can broadly be categorised as either link encryption, where each intermediary may encrypt data before passing it onto the next, or end-to-end encryption, where communications are encrypted such that only the legitimate end-points can have access to the unencrypted communication. End-to-end encryption is preferable for security because it avoids intermediaries being able to eavesdrop on communications and gives the end-points assurance that communications will indeed be encrypted all the way to their other communication partner. Current cellphone encryption standards are link encryption: the phone encrypts calls between it and the phone network using cryptographic keys stored on the Subscriber Identity Module (SIM). Within the phone network, encryption may also be present but the network provider still has access to unencrypted data, so even ignoring the vulnerability to fall-back attacks on the radio link, the network providers and their suppliers are weak points that are tempting for attackers to compromise. Recent examples of such attacks include the compromise of the phone networks of Vodafone in Greece (2004) and Belgacom in Belgium (2012), and the SIM card supplier Gemalto in France (2010). The identity of the Vodafone Greece hacker remains unknown (though the NSA is suspected) but the attacks against Belgacom and Gemalto were carried out by the UK signals intelligence agency -- GCHQ -- and only publicly revealed from the Snowden leaks, so it is quite possible there are others attacks which remain h idden. Email is typically only secured by link encryption, if at all, with HTTPS encrypting access to most webmail and Transport Layer Security (TLS) sometimes encrypting other communication protocols that carry email (SMTP, IMAP and POP). Again, the fact that intermediaries have access to plaintext creates a vulnerability, as demonstrated by the 2009 hack of Google's Gmail likely originating from China. End-to-end email encryption is possible using the OpenPGP or S/MIME protocols but their use is not common, primarily due to their poor usability, which in turn is at least partially a result of having to stay compatible with older insecure email standards. In contrast, instant messaging applications had more opportunity to start with a clean-slate and so this is where much innovation in terms of end-to-end security has taken place. Secure voice communication however has had less attention than instant messaging so in the remainder of the article we shall examine what should be expected of a secure voice communication system, and in particular see how one of the latest and up-coming protocols, MIKEY-SAKKE, which comes with UK government backing, meets these criteria. MIKEY-SAKKE and Secure Chorus MIKEY-SAKKE is the security protocol behind the Secure Chorus voice (and also video) encryption standard, commissioned and designed by GCHQ through their information security arm, CESG. GCHQ have announced that they will only certify voice encryption products through their Commercial Product Assurance (CPA) security evaluation scheme if the product implements MIKEY-SAKKE and Secure Chorus. As a result, MIKEY-SAKKE has a monopoly over the vast majority of classified UK government voice communication and so companies developing secure voice communication systems must implement it in order to gain access to this market. GCHQ can also set requirements of what products are used in the public sector and as well as for companies operating critical national infrastructure. ............. Conclusions and future work The design of MIKEY-SAKKE is motivated by the desire to allow undetectable and unauditable mass surveillance, which may be a requirement in exceptional scenarios such as within government departments processing classified information. However, in the vast majority of cases the properties that MIKEY-SAKKE offers are actively harmful for security. It creates a vulnerable single point of failure, which would require huge effort, skill and cost to secure -- requiring resource beyond the capability of most companies. Better options for voice encryption exist today, though they are not perfect either. In particular, more work is needed on providing scalable and usable protection against man-in-the-middle attacks, and protection of metadata for contact discovery and calls. More broadly, designers of protocols and systems need to appreciate the ethical consequences of their actions in terms of the political and power structures which naturally follow from their use. MIKEY-SAKKE is the lat est example to raise questions over the policy of many governments, including the UK, to put intelligence agencies in charge of protecting companies and individuals from spying, given the conflict of interest it creates. Update 2016-01-19: Fix broken links to GCHQ website, note that master key must be permanently available though not necessarily directly connected to the Internet, and mention suspicions that the NSA were involved in the Vodafone Greece compromise. The photograph above this article is of a AT&T TSD-3600E Telephone Security Device based around the Clipper key-escrow chip (© Matt Blaze). An edited version of this article will appear in the March 2016 special edition of IEEE Computer Magazine: Communications and Privacy under Surveillance. CC BY-ND 4.0 Insecure by design: protocols for encrypted phone calls by Steven J. Murdoch is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License. Published by Steven J. Murdoch Dr Steven J. Murdoch is a Royal Society University Research Fellow in the Information Security Research Group of University College London, working on developing metrics for security and privacy. His research interests include authentication/passwords, banking security, anonymous communications, censorship resistance and covert channels. He has worked with the OpenNet Initiative, investigating Internet censorship, and for the Tor Project, on improving the security and usability of the Tor anonymity system. His current research on developing methods to understand complex system security is supported by the Royal Society. He is also working on analysing the security of banking systems, especially Chip & PIN/EMV, and is Innovation Security Architect of Cronto, an online authentication technology provider and part of the VASCO group. _______________________________________________ The cryptography mailing list cryptography@metzdowd.com http://www.metzdowd.com/mailman/listinfo/cryptography