Category Archives: Cryptology

Cryptographic primitives, cryptanalysis

Meeting Snowden in Princeton

I’m at Princeton where Ed Snowden is due to speak by live video link in a few minutes, and have a discussion with Bart Gellmann.

Yesterday he spent four hours with a group of cryptographers from industry and academia, of which I was privileged to be one. The topic was the possible and likely countermeasures, both legal and technical, against state surveillance. Ed attended as the “Snobot”, a telepresence robot that let him speak to us, listen and move round the room, from a studio in Moscow. As well as over a dozen cryptographers there was at least one lawyer and at least one journalist familiar with the leaked documents. Yesterday’s meeting was under the Chatham House rule, so I may not say who said what; any new disclosures may have been made by Snowden, or by one of the journalists, or by one of the cryptographers who has assisted journalists with the material. Although most of what was discussed has probably appeared already in one place or another, as a matter of prudence I’m publishing these notes on the blog while I’m enjoying US first-amendment rights, and will sanitise them from my laptop before coming back through UK customs.

The problem of state surveillance is a global one rather than an NSA issue, and has been growing for years, along with public awareness of it. But we learned a lot from the leaks; for example, wiretaps on the communications between data centres were something nobody thought of; and it might do no harm to think a bit more about the backhaul in CDNs. (A website that runs TLS to a CDN and then bareback to the main server is actually worse than nothing, as we lose the ability to shame them.) Of course the agencies will go for the low-hanging fruit. Second, we also got some reassurance; for example, TLS works, unless the agencies have managed to steal or coerce the private keys, or hack the end systems. (This is a complex discussion given CDNs, problems with the CA ecology and bugs like Heartbleed.) And it’s a matter of record that Ed trusted his life to Tor, because he saw from the other side that it worked.

Third, the leaks give us a clear view of an intelligence analyst’s workflow. She will mainly look in Xkeyscore which is the Google of 5eyes comint; it’s a federated system hoovering up masses of stuff not just from 5eyes own assets but from other countries where the NSA cooperates or pays for access. Data are “ingested” into a vast rolling buffer; an analyst can run a federated search, using a selector (such as an IP address) or fingerprint (something that can be matched against the traffic). There are other such systems: “Dancing oasis” is the middle eastern version. Some xkeyscore assets are actually compromised third-party systems; there are multiple cases of rooted SMS servers that are queried in place and the results exfiltrated. Others involve vast infrastructure, like Tempora. If data in Xkeyscore are marked as of interest, they’re moved to Pinwale to be memorialised for 5+ years. This is one function of the MDRs (massive data repositories, now more tactfully renamed mission data repositories) like Utah. At present storage is behind ingestion. Xkeyscore buffer times just depend on volumes and what storage they managed to install, plus what they manage to filter out.

As for crypto capabilities, a lot of stuff is decrypted automatically on ingest (e.g. using a “stolen cert”, presumably a private key obtained through hacking). Else the analyst sends the ciphertext to CES and they either decrypt it or say they can’t. There’s no evidence of a “wow” cryptanalysis; it was key theft, or an implant, or a predicted RNG or supply-chain interference. Cryptanalysis has been seen of RC4, but not of elliptic curve crypto, and there’s no sign of exploits against other commonly used algorithms. Of course, the vendors of some products have been coopted, notably skype. Homegrown crypto is routinely problematic, but properly implemented crypto keeps the agency out; gpg ciphertexts with RSA 1024 were returned as fails.

With IKE the NSA were interested in getting the original handshakes, harvesting them all systematically worldwide. These are databased and indexed. The quantum type attacks were common against non-crypto traffic; it’s easy to spam a poisoned link. However there is no evidence at all of active attacks on cryptographic protocols, or of any break-and-poison attack on crypto links. It is however possible that the hacking crew can use your cryptography to go after your end system rather than the content, if for example your crypto software has a buffer overflow.

What else might we learn from the disclosures when designing and implementing crypto? Well, read the disclosures and use your brain. Why did GCHQ bother stealing all the SIM card keys for Iceland from Gemalto, unless they have access to the local GSM radio links? Just look at the roof panels on US or UK embassies, that look like concrete but are actually transparent to RF. So when designing a protocol ask yourself whether a local listener is a serious consideration.

In addition to the Gemalto case, Belgacom is another case of hacking X to get at Y. The kind of attack here is now completely routine: you look for the HR spreadsheet in corporate email traffic, use this to identify the sysadmins, then chain your way in. Companies need to have some clue if they’re to stop attacks like this succeeding almost trivially. By routinely hacking companies of interest, the agencies are comprehensively undermining the security of critical infrastructure, and claim it’s a “nobody but us” capability. however that’s not going to last; other countries will catch up.

Would opportunistic encryption help, such as using unauthenticated Diffie-Hellman everwhere? Quite probably; but governments might then simply compel the big service forms to make the seeds predictable. At present, key theft is probably more common than key compulsion in US operations (though other countries may be different). If the US government ever does use compelled certs, it’s more likely to be the FBI than the NSA, because of the latter’s focus on foreign targets. The FBI will occasionally buy hacked servers to run in place as honeypots, but Stuxnet and Flame used stolen certs. Bear in mind that anyone outside the USA has zero rights under US law.

Is it sensible to use medium-security systems such as Skype to hide traffic, even though they will give law enforcement access? For example, an NGO contacting people in one of the Stans might not want to incriminate them by using cryptography. The problem with this is that systems like Skype will give access not just to the FBI but to all sorts of really unsavoury police forces.

FBI operations can be opaque because of the care they take with parallel construction; the Lavabit case was maybe an example. It could have been easy to steal the key, but then how would the intercepted content have been used in court? In practice, there are tons of convictions made on the basis of cargo manifests, travel plans, calendars and other such plaintext data about which a suitable story can be told. The FBI considers it to be good practice to just grab all traffic data and memorialise it forever.

The NSA is even more cautious than the FBI, and won’t use top exploits against clueful targets unless it really matters. Intelligence services are at least aware of the risk of losing a capability, unlike vanilla law enforcement, who once they have a tool will use it against absolutely everybody.

Using network intrusion detection against bad actors is very much like the attack / defence evolution seen in the anti-virus business. A system called Tutelage uses Xkeyscore infrastructure and matches network traffic against signatures, just like AV, but it has the same weaknesses. Script kiddies are easily identifiable from their script signatures via Xkeyscore, but the real bad actors know how to change network signatures, just as modern malware uses packers to become highly polymorphic.

Cooperation with companies on network intrusion detection is tied up with liability games. DDoS attacks from Iran spooked US banks, which invited the government in to snoop on their networks, but above all wanted liability protection.

Usability is critical. Lots of good crypto never got widely adopted as it was too hard to use; think of PGP. On the other hand, Tails is horrifically vulnerable to traditional endpoint attacks, but you can give it as a package to journalists to use so they won’t make so many mistakes. The source has to think “How can I protect myself?” which makes it really hard, especially for a source without a crypto and security background. You just can’t trust random journalists to be clueful about everything from scripting to airgaps. Come to think of it, a naive source shouldn’t trust their life to securedrop; he should use gpg before he sends stuff to it but he won’t figure out that it’s a good idea to suppress key IDs. Engineers who design stuff for whistleblowers and journalists must be really thoughtful and careful if they want to ensure their users won’t die when they screw up. The goal should be that no single error should be fatal, and so long as their failures aren’t compounded the users will stay alive. Bear in mind that non-roman-language countries use numeric passwords, and often just 8 digits. And being a target can really change the way you operate. For example, password managers are great, but not for someone like Ed, as they put too many of the eggs in one basket. If you’re a target, create a memory castle, or a token that can be destroyed on short notice. If you’re a target like Ed, you have to compartmentalise.

On the policy front, one of the eye-openers was the scale of intelligence sharing – it’s not just 5 eyes, but 15 or 35 or even 65 once you count all the countries sharing stuff with the NSA. So how does governance work? Quite simply, the NSA doesn’t care about policy. Their OGC has 100 lawyers whose job is to “enable the mission”; to figure out loopholes or new interpretations of the law that let stuff get done. How do you restrain this? Could you use courts in other countries, that have stronger human-rights law? The precedents are not encouraging. New Zealand’s GCSB was sharing intel with Bangladesh agencies while the NZ government was investigating them for human-rights abuses. Ramstein in Germany is involved in all the drone killings, as fibre is needed to keep latency down low enough for remote vehicle pilots. The problem is that the intelligence agencies figure out ways to shield the authorities from culpability, and this should not happen.

Jurisdiction is a big soft spot. When will CDNs get tapped on the shoulder by local law enforcement in dodgy countries? Can you lock stuff out of particular jurisdictions, so your stuff doesn’t end up in Egypt just for load-balancing reasons? Can the NSA force data to be rehomed in a friendly jurisdiction, e.g. by a light DoS? Then they “request” stuff from a partner rather than “collecting” it.

The spooks’ lawyers play games saying for example that they dumped content, but if you know IP address and file size you often have it; and IP address is a good enough pseudonym for most intel / LE use. They deny that they outsource to do legal arbitrage (e.g. NSA spies on Brits and GCHQ returns the favour by spying on Americans). Are they telling the truth? In theory there will be an MOU between NSA and the partner agency stipulating respect for each others’ laws, but there can be caveats, such as a classified version which says “this is not a binding legal document”. The sad fact is that law and legislators are losing the capability to hold people in the intelligence world to account, and also losing the appetite for it.

The deepest problem is that the system architecture that has evolved in recent years holds masses of information on many people with no intelligence value, but with vast potential for political abuse.

Traditional law enforcement worked on individualised suspicion; end-system compromise is better than mass search. Ed is on the record as leaving to the journalists all decisions about what targeted attacks to talk about, as many of them are against real bad people, and as a matter of principle we don’t want to stop targeted attacks.

Interference with crypto in academia and industry is longstanding. People who intern with a clearance get a “lifetime obligation” when they go through indoctrination (yes, that’s what it’s called), and this includes pre-publication review of anything relevant they write. The prepublication review board (PRB) at the CIA is notoriously unresponsive and you have to litigate to write a book. There are also specific programmes to recruit cryptographers, with a view to having friendly insiders in companies that might use or deploy crypto.

The export control mechanisms are also used as an early warning mechanism, to tip off the agency that kit X will be shipped to country Y on date Z. Then the technicians can insert an implant without anyone at the exporting company knowing a thing. This is usually much better than getting stuff Trojanned by the vendor.

Western governments are foolish to think they can develop NOBUS (no-one but us) technology and press the stop button when things go wrong, as this might not be true for ever. Stuxnet was highly targeted and carefully delivered but it ended up in Indonesia too. Developing countries talk of our first-mover advantage in carbon industrialisation, and push back when we ask them to burn less coal. They will make the same security arguments as our governments and use the same techniques, but without the same standards of care. Bear in mind, on the equities issue, that attack is way way easier than defence. So is cyber-war plausible? Politically no, but at the expert level it might eventually be so. Eventually something scary will happen, and then infrastructure companies will care more, but it’s doubtful that anyone will do a sufficiently coordinated attack on enough diverse plant through different firewalls and so on to pose a major threat to life.

How can we push back on the poisoning of the crypto/security community? We have to accept that some people are pro-NSA while others are pro-humanity. Some researchers do responsible disclosure while others devise zero-days and sell them to the NSA or Vupen. We can push back a bit by blocking papers from conferences or otherwise denying academic credit where researchers prefer cash or patriotism to responsible disclosure, but that only goes so far. People who can pay for a new kitchen with their first exploit sale can get very patriotic; NSA contractors have a higher standard of living than academics. It’s best to develop a culture where people with and without clearances agree that crypto must be open and robust. The FREAK attack was based on export crypto of the 1990s.

We must also strengthen post-national norms in academia, while in the software world we need transparency, not just in the sense of open source but of business relationships too. Open source makes it harder for security companies to sell different versions of the product to people we like and people we hate. And the NSA may have thought dual-EC was OK because they were so close to RSA; a sceptical purchaser should have observed how many government speakers help them out at the RSA conference!

Secret laws are pure poison; government lawyers claim authority and act on it, and we don’t know about it. Transparency about what governments can and can’t do is vital.

On the technical front, we can’t replace the existing infrastructure, so it won’t be possible in the short term to give people mobile phones that can’t be tracked. However it is possible to layer new communications systems on top of what already exists, as with the new generation of messaging apps that support end-to-end crypto with no key escrow. As for whether such systems take off on a large enough scale to make a difference, ultimately it will all be about incentives.

Security Protocols 2015

I’m at the 23rd Security Protocols Workshop, whose theme this year is is information security in fiction and in fact. Engineering is often inspired by fiction, and vice versa; what might we learn from this?

I will try to liveblog the talks in followups to this post.

There exists a classical model of the photon after all

Many people assume that quantum mechanics cannot emerge from classical phenomena, because no-one has so far been able to think of a classical model of light that is consistent with Maxwell’s equations and reproduces the Bell test results quantitatively.

Today Robert Brady and I unveil just such a model. It turns out that the solution was almost in plain sight, in James Clerk Maxwell’s 1861 paper On Phyiscal Lines of Force in which he derived Maxwell’s equations, on the assumption that magnetic lines of force were vortices in a fluid. Updating this with modern knowledge of quantised magnetic flux, we show that if you model a flux tube as a phase vortex in an inviscid compressible fluid, then wavepackets sent down this vortex obey Maxwell’s equations to first order; that they can have linear or circular polarisation; and that the correlation measured between the polarisation of two cogenerated wavepackets is exactly the same as is predicted by quantum mechanics and measured in the Bell tests.

This follows work last year in which we explained Yves Couder’s beautiful bouncing-droplet experiments. There, a completely classical system is able to exhibit quantum-mechanical behaviour as the wavefunction ψ appears as a modulation on the driving oscillation, which provides coherence across the system. Similarly, in the phase vortex model, the magnetic field provides the long-range order and the photon is a modulation of it.

We presented this work yesterday at the 2015 Symposium of the Trinity Mathematical Society. Our talk slides are here and there is an audio recording here.

If our sums add up, the consequences could be profound. First, it will explain why quantum computers don’t work, and blow away the security ‘proofs’ for entanglement-based quantum cryptosystems (we already wrote about that here and here). Second, if the fundamental particles are just quasiparticles in a superfluid quantum vacuum, there is real hope that we can eventually work out where all the mysterious constants in the Standard Model come from. And third, there is no longer any reason to believe in multiple universes, or effects that propagate faster than light or backward in time – indeed the whole ‘spooky action at a distance’ to which Einstein took such exception. He believed that action in physics was local and causal, as most people do; our paper shows that the main empirical argument against classical models of reality is unsound.

Nikka – Digital Strongbox (Crypto as Service)

Imagine, somewhere in the internet that no-one trusts, there is a piece of hardware, a small computer, that works just for you. You can trust it. You can depend on it. Things may get rough but it will stay there to get you through. That is Nikka, it is the fixed point on which you can build your security and trust. [Now as a Kickstarter project]

You may remember our proof-of-concept implementation of a password protection for servers – Hardware Scrambling (published here in March). The password scrambler was a small dongle that could be plugged to a Linux computer (we used Raspberry Pi). Its only purpose was to provide a simple API for encrypting passwords (but it could be credit cards or anything else up to 32 bytes of length). The beginning of something big?

It received some attention (Ars Technica, Slashdot, LWN, …), certainly more than we expected at the time. Following discussions have also taught us a couple of lessons about how people (mostly geeks in this contexts) view security – particularly about the default distrust expressed by those who discussed articles describing our password scrambler.

We eventually decided to build a proper hardware cryptographic platform that could be used for cloud applications. Our requirements were simple. We wanted something fast, “secure” (CC EAL5+ or even FIPS140-2 certified), scalable, easy to use (no complicated API, just one function call) and to be provided as a service so no-one has to pay upfront the price of an HSM if they just want to have a go at using proper cryptography for their new or old application. That was the beginning of Nikka.

nikka_setup

This is our concept: Nikka comprises a set of powerful servers installed in secure data centres. These servers can create clusters delivering high-availability and scalability for their clients. Secure hardware forms the backbone of each server that provides an interface for simple use. The second part of Nikka are user applications, plugins, and libraries for easy deployment and everyday “invisible” use. Operational procedures, processes, policies, and audit logs then guarantee that what we say is actually being done.

2014-07-04 08.17.35We have been building it for a few months now and the scalable cryptographic core seems to work. We have managed to run long-term tests of 150 HMAC transactions per second (HMAC & RNG for password scrambling) on a small development platform while fully utilising available secure hardware. The server is hosted at ideaSpace and we use it to run functional, configuration and load tests.

We have never before designed a system with so many independent processes – the core is completely asynchronous (starting with Netty for a TCP interface) and we have quickly started to appreciate detailed trace logging we’ve implemented from the very beginning. Each time we start digging we find something interesting. Real-time visualisation of the performance is quite nice as well.
real_time_monitoring

Nikka is basically a general purpose cryptographic engine with middleware layer for easy integration. The password HMAC is this time used only as one of test applications. Users can share or reserve processing units that have Common Criteria evaluations or even FIPS140-2 certification – with possible physical hardware separation of users.

If you like what you have read so far, you can keep reading, watching, supporting at Kickstarter. It has been great fun so far and we want to turn it into something useful in 2015. If it sounds interesting – maybe you would like to test it early next year, let us know! @DanCvrcek

Light Blue Touchpaper now on HTTPS

Light Blue Touchpaper now supports TLS, so as to protect passwords and authentication cookies from eavesdropping. TLS support is provided by the Pound load-balancer, because Varnish (our reverse-proxy cache) does not support TLS.

The configuration is intended to be a reasonable trade-off between security and usability, and gets an A– on the Qualys SSL report. The cipher suite list is based on the very helpful Qualys Security Labs recommendations and Apache header re-writing sets the HttpOnly and Secure cookie flags to resist cookie hijacking.

As always, we might have missed something, so if you notice problems such as incompatibilities with certain browsers, then please let us know on <lbt-admin@cl.cam.ac.uk>. or in the comments.

The pre-play vulnerability in Chip and PIN

Today we have published a new paper: “Chip and Skim: cloning EMV cards with the pre-play attack”, presented at the 2014 IEEE Symposium on Security and Privacy. The paper analyses the EMV protocol, the leading smart card payment system with 1.62 billion cards in circulation, and known as “Chip and PIN” in English-speaking countries. As a result of the Target data breach, banks in the US (which have lagged behind in Chip and PIN deployment compared to the rest of the world) have accelerated their efforts to roll out Chip and PIN capable cards to their customers.

However, our paper shows that Chip and PIN, as currently implemented, still has serious vulnerabilities, which might leave customers at risk of fraud. Previously we have shown how cards can be used without knowing the correct PIN, and that card details can be intercepted as a result of flawed tamper-protection. Our new paper shows that it is possible to create clone chip cards which normal bank procedures will not be able to distinguish from the real card.

When a Chip and PIN transaction is performed, the terminal requests that the card produces an authentication code for the transaction. Part of this transaction is a number that is supposed to be random, so as to stop an authentication code being generated in advance. However, there are two ways in which the protection can by bypassed: the first requires that the Chip and PIN terminal has a poorly designed random generation (which we have observed in the wild); the second requires that the Chip and PIN terminal or its communications back to the bank can be tampered with (which again, we have observed in the wild).

To carry out the attack, the criminal arranges that the targeted terminal will generate a particular “random” number in the future (either by predicting which number will be generated by a poorly designed random number generator, by tampering with the random number generator, or by tampering with the random number sent to the bank). Then the criminal gains temporary access to the card (for example by tampering with a Chip and PIN terminal) and requests authentication codes corresponding to the “random” number(s) that will later occur. Finally, the attacker loads the authentication codes on to the clone card, and uses this card in the targeted terminal. Because the authentication codes that the clone card provides match those which the real card would have provided, the bank cannot distinguish between the clone card and the real one.

Because the transactions look legitimate, banks may refuse to refund victims of fraud. So in the paper we discuss how bank procedures could be improved to detect whether this attack has occurred. We also describe how the Chip and PIN system could be improved. As a result of our research, work has started on mitigating one of the vulnerabilities we identified; the certification requirements for random number generators in Chip and PIN terminals have been improved, though old terminals may still be vulnerable. Attacks making use of tampered random number generators or communications are more challenging to prevent and have yet to be addressed.

Update (2014-05-20): There is press coverage of this paper in The Register, SC Magazine UK and Schneier on Security.
Update (2014-05-21): Also now covered in The Hacker News.

Current state of anonymous email usability

As part of another project, I needed to demonstrate how the various user-interface options for sending anonymous email through Mixmaster appeared to the email sender. This is very difficult to explain in words, so I recorded some screencasts. The tools I used were the Mixmaster command line tool, the Mutt email client with Mixmaster plugin, QuickSilver Lite, and finally a web-based interface.

The project is now over, but in case these screencasts are of wider interest, I’ve put them on YouTube.

Overall, the usability of Mixmaster is not great. All of the secure options are difficult to configure and use (QuickSilver Lite is probably the best), emails take a long time to be sent, recipients of anonymous email can’t send replies, and there is a high chance that the email will be dropped en-route.

Continue reading Current state of anonymous email usability

Financial cryptography 2014

I will be trying to liveblog Financial Cryptography 2014. I just gave a keynote talk entitled “EMV – Why Payment Systems Fail” summarising our last decade’s research on what goes wrong with Chip and PIN. There will be a paper on this out in a few months; meanwhile here’s the slides and here’s our page of papers on bank security.

The sessions of refereed papers will be blogged in comments to this post.

Why bouncing droplets are a pretty good model of quantum mechanics

Today Robert Brady and I publish a paper that solves an outstanding problem in physics. We explain the beautiful bouncing droplet experiments of Yves Couder, Emmanuel Fort and their colleagues.

For years now, people interested in the foundations of physics have been intrigued by the fact that droplets bouncing on a vibrating tray of fluid can behave in many ways like quantum mechanical particles, with single-slit and double-slit diffraction, tunneling, Anderson localisation and quantised orbits.

In our new paper, Robert Brady and I explain why. The wave field surrounding the droplet is, to a good approximation, Lorentz covariant with the constant c being the speed of surface waves. This plus the inverse square force between bouncing droplets (which acts like the Coulomb force) gives rise to an analogue of the magnetic force, which can be observed clearly in the droplet data. There is also an analogue of the Schrödinger equation, and even of the Pauli exclusion principle.

These results not only solve a fascinating puzzle, but might perhaps nudge more people to think about novel models of quantum foundations, about which we’ve written three previous papers.