Ross Anderson

[Research] [Blog] [Politics] [My Book] [Music] [Contact Details]

Here is a survey paper on security economics which I gave at Softint 2007 on January 20th; my slides; and a shorter survey that was recently published in Science. See also my Economics and Security Resource Page.

2006 blog highlights included technical papers on topics from protecting power-line communications to the Man-in-the-Middle Defence, as well as a major report on the safety and privacy of children's databases for the UK Information Commissioner, which got a lot of publicity. I ended the year by debating health privacy on the Today programme with health minister Lord Warner, who resigned shortly aftewards. 2005 blog highlights included research papers on The topology of covert conflict, on combining cryptography with biometrics, on Sybil-resistant DHT routing, and on Robbing the bank with a theorem prover; and a survey paper on cryptographic processors, a shortened version of which appeared in the February 2006 Proceedings of the IEEE. 2004 highlights included papers on cipher composition, key establishment in ad-hoc networks and the economics of censorship resistance. I also lobbied for amentments to the EU IP Enforcement Directive and organised a workshop on copyright which led to a common position adopted by many European NGOs.

I am Professor of Security Engineering at the Computer Laboratory. I supervise a number of research students - Jolyon Clulow, Hao Feng, Stephen Lewis, Tyler Moore, Shishir Nagaraja Andy Ozment and Robert Watson. Richard Clayton, Steven Murdoch and Sergei Skorobogatov are postdocs. Mike Bond, Vashek Matyas and Andrei Serjantov are former postdocs. Jong-Hyeon Lee, Frank Stajano, Fabien Petitcolas, Harry Manifavas, Markus Kuhn, Ulrich Lang, Jeff Yan, Susan Pancho, Mike Bond, George Danezis, Sergei Skorobogatov, Hyun-Jin Choi and Richard Clayton have earned PhDs.

My other research interests include:

• Economics of information security - including material on `Trusted Computing'
• Peer-to-Peer systems - including the Eternity Service and the Cocaine auction protocol
• Robustness of cryptographic protocols - including `Programming Satan's Computer'
• Reliability of security systems - including ATM fraud and smartcard hacking
• Analysis and design of cryptographic algorithms - including our AES candidate Serpent
• Information hiding - including Soft Tempest and attacks on copyright marking systems
• Security of clinical information systems - including the Iceland database
• Privacy and freedom issues - including FIPR and `Trusted Computing'

Many of my papers are available in html and/or pdf, but some of the older technical ones are in postscript, for which you can download a viewer here. By default, when I post a paper here I license it under the relevant Creative Commons license, so you may redistribute it but not modify it. I may subsequently assign the residual copyright to an academic publisher.

Economics of information security

Over the last few years, it's become clear that many systems fail not for technical reasons so much as from misplaced incentives - often the people who could protect them are not the people who suffer the costs of faulure. There are also many questions with an economic dimension as well as a technical one. For example, will digital signatures make electronic commerce more secure? Is so-called `trusted computing' a good idea, or just another way for Microsoft to make money? And what about all the press stories about `Internet hacking' - is this threat serious, or is it mostly just scaremongering by equipment vendors? It's not enough for security engineers to understand ciphers; we have to understand incentives as well. This has led to a rapidly growing interest in `security economics', a discipline which I helped to found. I maintain the Economics and Security Resource Page, and my research contributions include the following.

• The Economics of Information Security - A Survey and Open Questions is a paper I'm giving at the Conference on the Economics of the Software and Internet Industries in January 2007. A much shorter version, called simply The Economics of Information Security, was published in Science in October 2006. This survey papers are a work in progress: we plan to produce more detailed and extensive versions over time.
• The topology of covert conflict is rather topical - how can the police best target an underground organisation given some knowledge of its patterns of communication? And how might they in turn react to various law-enforcement strategies? We present a framework combining ideas from network analysis and evolutionary game theory to explore the interaction of attack and defence strategies in networks. Although we started out thinking about computer viruses, our work suggests explanations of a number of aspects of modern conflict generally.
• Why Information Security is Hard - An Economic Perspective was the paper that got information security people thinking about the subject. It applies economic analysis to explain many phenomena that security people had found to be pervasive but perplexing. Why do mass-market software products such as Windows contain so many security bugs? Why are their security mechanisms so difficult to manage? Why are government evaluation schemes, such as the Orange Book and the Common Criteria, so bad? This paper was presented at the Applications Security conference in December 2001, and also as an invited talk at SOSP 2001.
• The hot political issue is `Trusted Computing'. My `Trusted Computing' FAQ analysed this Intel/Microsoft initiative to install digital rights management hardware in every computer, PDA and mobile phone. `TC' will please Hollywood by making it hard to pirate music and videos; and it will please Microsoft by making it harder to pirate software. But TC could have disturbing consequences for privacy, censorship, and innovation. Cryptography and Competition Policy - Issues with `Trusted Computing' is an economic analysis I gave at WEIS2003 and also as an invited talk at PODC 2003. TC will help Microsoft lock in its customers more tightly, so it can charge more. The proposed mechanisms could also have some disturbing consequences for privacy, censorship, and innovation. There is a shortened version of the paper that appeared in a special issue of Upgrade, and a French translation. I spoke about TC at the "Trusted Computing Group" Symposium, at PODC, and at the Helsinki IPR workshop. There's also a neat video clip. TC is not just an isolated engineering and policy issue; it is related to the IP Enforcement Directive on the policy front, and new content standards such as DTCP, which will be built into consumer electronics and also into PC motherboards. The row about `Trusted Computing' was ignited by a paper on the security of free and open source software I gave at a conference on Open Source Software Economics in Toulouse. This paper got press coverage in the New York Times, slashdot, news.com and The Register. Its second part is about TC
• In the first part of my Toulouse paper, I show that the usual argument about open source security - whether source access makes it easier for the defenders to find and fix bugs, or makes it easier for the attackers to find and exploit them - is misdirected. Under standard assumptions used by the reliability growth modelling community, the two will exactly cancel each other out. That means that whether open or closed systems are more secure in a given situation will depend on whether, and how, the application deviates from the standard assumptions. The ways in which this can happen, and either open or closed be better in some specific application, are explored in a later paper, Open and Closed Systems are Equivalent (that is, in an ideal world) which appeared as a chapter in a book entitled Perspectives on Free and Open Source Software (you can download the whole book for free by clicking on that link). This also got some press coverage.
• On Dealing with Adversaries Fairly applies election theory (also known as social choice theory) to the problem of shared control in distributed systems. It shows how a number of reputation systems proposed for use in peer-to-peer applications might be improved. It appeared at WEIS 2004.
• The Economics of Censorship Resistance examines when it is better for defenders to aggregate or disperse. Should file-sharers build one huge system like gnutella and hope for safety in numbers, or would a loose federation of fan clubs for different bands work better? More generally, what are the tradeoffs between diversity and solidarity when conflict threatens? (This is a live topic in social policy at the moment - see David Goodhart's essay, and a response in the Economist.) This paper also appeared at WEIS 2004.
• Here are papers on The Initial Costs and Maintenance Costs of Protocols, which I gave at Security Protocols 05, and How Much is Location Privacy Worth? which I gave at WEIS 05.

Our annual bash is the Workshop on Economics and Information Security. My Economics and Security Resource Page provides a guide to the literature and to what else is on. There is also a web page on the economics of privacy, maintained by Alessandro Acquisti.

Peer-to-Peer systems

Since about the middle of 2000, there has been an explosion of interest in peer-to-peer networking - the business of building useful systems out of large numbers of intermittently connected machines, with virtual infrastructures that are tailored to the application. One of the seminal papers in the field was The Eternity Service, which I presented at Pragocrypt 96. I had been alarmed by the Scientologists' success at closing down the penet remailer in Finland, and had been personally threatened by bank lawyers who wanted to suppress knowledge of the vulnerabilities of ATM systems (see here for a later incident). This taught me that electronic publications can be easy for the rich and the ruthless to suppress. They are usually kept on just a few servers, whose owners can be sued or coerced. To me, this seemed uncomfortably like books in the Dark Ages: the modern era only started once the printing press enabled seditious thoughts to be spread too widely to ban. The Eternity Service was conceived as a means of putting electronic documents as far outwith the censor's grasp as possible. (The concern that motivated me has since materialised; a UK court judgment has found that a newspaper's online archives can be altered by order of a court to remove a libel.)

But history never repeats itself exactly, and the real fulcrum of censorship in cyberspace turned out to be not sedition, or vulnerability disclosure, or even pornography, but copyright. Hollywood's action against Napster led to my Eternity Service ideas being adopted by many systems including Publius and Freenet. Many of these developments were described in an important book, and the first academic conference on peer-to-peer systems was held in March 2002 at MIT. The field has since become very active. See also Richard Stallman's classic, The Right to Read.

My contributions since the Eternity paper include:

• I've been helping upgrade the security of Homeplug, an industry standard for broadband communication over the power mains. A paper on what we did and why appeared at SOUPS. This is a good worked example of how to do key establishment in a real peer-to-peer system. The core problem is this: how can you be sure you're recruiting the right device to your network, rather than a similar one nearby?
• Sybil-resistant DHT routing appeared at ESORICS 2005 and showed how we can make peer-to-peer systems more robust against disrutpive attacks if we know which nodes introduced which other nodes. The convergence of computer science and social network theory is an interesting recent phenomenon, and not limited to search and recommender systems.
• Key Infection - Smart trust for Smart Dust appeared at ICNP 2004 and presents a radically new approach to key management in sensor and peer-to-peer networks. Peers establish keys opportunistically and use resilience mechanisms to fortify the system against later node compromise. This work challenges the old assumption that authentication is largely a bootstrapping problem.
• The Economics of Censorship Resistance examines when it is better for defenders to aggregate or disperse. Should file-sharers build one huge system like gnutella and hope for safety in numbers, or would a loose federation of fan clubs for different bands work better?
• A New Family of Authentication Protocols presented our `Guy Fawkes Protocol', which enables users to sign messages using only two computations of a hash function and one reference to a timestamping service. This led to many protocols for signing digital streams. Our paper also raises foundational questions about the definition of a digital signature.
• Peer-to-peer techniques are not just about creating virtual machines out of many distributed PCs on the Internet, but apply also to other environments where communication is intermittent. Mobile communications, personal area networks and piconets are another rapidly developing field. The Resurrecting Duckling: Security Issues for Ad-hoc Wireless Networks describes how to do key management between low-cost devices that can talk to each other using radio or infrared, and without either the costs or privacy problems of centralised trusted third parties. (There's also a journal version of the paper here.)
• The study of distributed systems which are hidden, deniable or difficult to censor might be described as `subversive group computing'. Our seminal publication in this thread was The Cocaine Auction Protocol which explored how commercial transactions can be conducted between mutually mistrustful principals with no trusted arbitrator, while giving a high degree of privacy against traffic analysis.
• I have done some work with our university library on how to secure a digital repository. This grew out of a thread on web security:
• The Eternal Resource Locator: An Alternative Means of Establishing Trust on the World Wide Web investigated how to protect naming and indexing information and showed how to embed trust mechanisms in html documents. It was motivated by a project by colleagues at our medical school to protect the electronic version of the British National Formulary. It followed work reported in Secure Books: Protecting the Distribution of Knowledge, which describes a project to protect the authenticity and integrity of electronically distributed treatment protocols. Later work included Jikzi, an authentication framework for electronic publishing, which works by integrating ERL-type ideas into XML and which led to a startup. There are both general and technical papers on Jikzi.
• The XenoService - A Distributed Defeat for Distributed Denial of Service described defeating distributed denial of service attacks using a network of web hosts that can respond to an attack on a site by replicating it rapidly and widely. It used Xenoservers, developed at Cambridge for distributed hosting. This technique is now widely used.

• API Level Attacks on Embedded Systems was our first detailed paper on a powerful new way to attack crypto processors. Even if a device is physically tamper-proof, it can often be defeated by sending it some sequence of transactions which causes it to leak the key. We've broken pretty well every security processor we've looked at, at least once. This line of research originated at Protocols 2000 with my paper The Correctness of Crypto Transaction Sets, and more followed in my book. A recent paper, Robbing the bank with a theorem prover, shows how to apply some advanced tools to the problem, and some ideas for future research can be found in Protocol Analysis, Composability and Computation. There is a survey of the state of the art in late 2005 in a survey of cryptographic processors, a shortened version of which appeared in the February 2006 Proceedings of the IEEE.
• Programming Satan's Computer is a phrase Roger Needham and I coined to express the difficulty of designing cryptographic protocols; it has recently been popularised by Bruce Schneier (see, for example, his foreword to my book). The problem of designing programs which run robustly on a network containing a malicious adversary is rather like trying to program a computer which gives subtly wrong answers at the worst possible moments.
• Robustness p rinciples for public key protocols gives a number of attacks on protocols based on public key primitives. It also puts forward some principles which can help us to design robust protocols, and to find attacks on other people's designs. It appeared at Crypto 95.
• The Cocaine Auction Protocol explores how transactions can be conducted between mutually mistrustful principals with no trusted arbitrator, even in environments where anonymous communications make most of the principals untraceable.
• NetCard - A Practical Electronic Cash Scheme presents research on micropayment protocols for use in electronic commerce. We invented tick payments simultaneously with Torben Pedersen and with Ron Rivest and Adi Shamir; we all presented our work at Protocols 96. Our paper discusses how tick payments can be made robust against attacks on either the legacy credit card infrastructure or next generation PKIs.
• The GCHQ Protocol and its Problems pointed out a number of flaws in a key management protocol widely used in the UK government. It was promoted by GCHQ as a European alternative to Clipper, until we shot it down with this paper at Eurocrypt 97. Many of the criticisms we developed here also apply to the more recent, pairing-based cryptosystems.
• The Formal Verification of a Payment System describes the first use of formal methods to verify an actual payment protocol, which was (and still is) used in an electronic purse product (VISA's COPAC card). This is a teaching example I use to get the ideas of the BAN logic across to undergraduates. There is further detailed information in a technical report, which combines papers given at ESORICS 92 and Cardis 94.
• An Attack on Server Assisted Authentication Protocols appeared in Electronics Letters in 1992. It breaks a digital signature protocol.
• On Fortifying Key Negotiation Schemes with Poorly Chosen Passwords presents a simple way of achieving the same result as protocols such as EKE, namely preventing middleperson attacks on Diffie-Hellman key exchange between two people whose shared secret could be guessed by the enemy.

Protocols have been the stuff of high drama. Citibank asked the High Court to gag the disclsoure of certain crypto API vulnerabilities that affect a number of systems used in banking. I wrote to the judge opposing this; a gagging order was still imposed, although in slightly less severe terms than Citibank had requested. The trial was in camera, the banks' witnesses didn't have to answer questions about vulnerabilities, and new information revealed about these vulnerabilities in the course of the trial may not be disclosed in England or Wales. Information already in the public domain was unaffected. The vulnerabilities were discovered by Mike Bond and me while acting as the defence experts in a phantom withdrawal court case, and independently discovered by the other side's expert, Jolyon Clulow, who later joined us as a research student. They are of significant scientific interest, as well as being relevant to the rights of the growing number of people who suffer phantom withdrawals from their bank accounts worldwide. Undermining the fairness of trials and forbidding discussion of vulnerabilities isn't the way forward. See press coverage by the New Scientist, the Register, Slashdot, news.com, and Zdnet.

• Why Cryptosystems Fail may have been cited more than anything else I've written. This version appeared at ACMCCS 93 and explains how ATM fraud was done in the early 1990s. Liability and Computer Security - Nine Principles took this work further, and examines the problems with relying on cryptographic evidence. The recent introduction of EMV ('chip and PIN') was supposed to fix the problem, but hasn't: Phish and Chips documents protocol weaknesses in EMV, while The Man-in-the-Middle Defence shows how to turn protocol weaknesses to advantage. For example, a bank customer can take an electronic attorney along to a chip-and-PIN transaction to help ensure that neither the bank nor the merchant rips him off. This story will run and run.
• On a New Way to Read Data from Memory describes techniques we developed that use lasers to read out memory contents directly from a chip, without using the read-out circuits provided by the vendor. This can defeat access controls and even recover data from damaged devices. Collaborators at Louvain have developed ways to do this using electromagnetic induction, which are also described. The work builds on methods described in an earlier paper, on Optical Fault Induction Attacks. This showed how laser pulses could be used to induce faults in smartcards that would leak secret information. We can write arbitrary values into registers or memory, reset protection bits, break out of loops, and cause all sorts of mayhem. That paper made the front page of the New York Times; it also got covered by the New Scientist and slashdot. It was presented at CHES 2002.
• After we discovered the above attacks, we developed a new, more secure, CPU technology for use in smartcards and similar products. It uses redundant failure-evident logic to thwart attacks based on fault induction or power analysis. Our first paper on this technology won the best presentation award in April at Async 2002. Our latest journal paper has recent test results.
• Our classic paper on hardware security, Tamper Resistance - A Cautionary Note, describes how to penetrate the smartcards and secure microcontrollers of the mid-1990s. It won the Best Paper award at the 1996 Usenix Electronic Commerce Workshop and caused a lot of controversy. Our second paper on the subject was Low Cost Attacks on Tamper Resistant Devices, which describes a number of tricks low budget attackers can use. See also the home page of our hardware security laboratory which brings together our smartcard and Tempest work, and Markus Kuhn's page of links to hardware attack resources.
• On the Reliability of Electronic Payment Systems is another of the papers that followed naturally from working on ATMs. It looks at the reliability of prepayment electricity meters, and appeared in the May 1996 issue of the IEEE Transactions on Software Engineering. An ealier version, entitled Cryptographic Credit Control in Pre-Payment Metering Systems, appeared at the 1995 IEEE Symposium on Security and Privacy. A later paper on this subject is The design of future pre-payment systems, which discussed how we could apply what we'd learned to support utility meter interworking in the UK after deregulation.
• On the Security of Digital Tachographs looks at the techniques used to manipulate the tachographs that are used in Europe to police truck and bus drivers' hours. It tried (with some success) to predict how the introduction of smartcard-based digital tachographs throughout Europe from the year 2000 would affect fraud and tampering. This work was done for the Department of Transport.
• How to Cheat at the Lottery is a paper reporting a novel and, I hope, entertaining experiment in software requirements engineering. The lessons it teaches have the potential to cut the cost of developing safety critical and security critical software, and also to reduce the likelihood that specification errors will lead to disastrous failures.
• The Grenade Timer describes a novel way to protect low-cost processors against denial-of-service attacks, by limiting the number of processing cycles an application program can consume.
• The Millennium Bug - Reasons Not to Panic describes our experience in coping with the bug at Cambridge University and elsewhere. This paper correctly predicted that the bug wouldn't bite very hard. (Journalists were not interested, despite a major press release by the University.)
• The Memorability and Security of Passwords -- Some Empirical Results tackles an old problem - how do you train users to choose passwords that are easy to remember but hard to guess? There's a lot of `folk wisdom' on this subject but little that would pass muster by the standards of applied psychology. So we did a randomized controlled trial with a few hundred first year science students. While we confirmed some common beliefs, we debunked some others. This has become one of the classic papers on security usability.
• Murphy's law, the fitness of evolving species, and the limits of software reliability shows how we can apply the techniques of statistical thermodynamics to the failure modes of any complex logical system that evolves under testing. It provides a common mathematical model for the reliability growth of complex computer systems and for biological evolution. Its findings are in close agreement with empirical data. This paper inspired later work in security economics.
• Security Policies play a central role in secure systems engineering. They provide a concise statement of the kind of protection a system is supposed to achieve. A security policy should be driven by a realistic threat model, and should in turn be used as the foundation for the design and testing of protection mechanisms. This article is a security policy tutorial.
• Here is a paper on combining cryptography with biometrics, which shows that in those applications where you can benefit from biometrics, you don't need a large central database (as proposed in the ID card Bill). There are smarter, more resilient, and less privacy-invasive ways to arrange things.

The papers on physical security by Roger Johnston's team are also definitely worth a look, and there's an old leaked copy of the NSA Security Manual that you can download (also as latex).

Reports of an attack on the hash function SHA have made Tiger, which Eli Biham and I designed in 1995, a popular choice of cryptographic hash function. I also worked with Eli, and with Lars Knudsen, to develop Serpent - a candidate block cipher for the Advanced Encryption Standard. Serpent won through to the final of the competition and got the second largest number of votes. Another of my contributions was founding the series of workshops on Fast Software Encryption.

Other papers on cryptography and cryptanalysis include the following.

• The Dancing Bear - A New Way of Composing Ciphers presents a new way to combine crypto primitives. Previously, to decrypt using (say) any three out of five keys, the keys all had to be of the same type (such as RSA keys). With my new construction, you can mix and match - RSA, AES, even one-time pad. The paper appeared at the 2004 Protocols Workshop; an earlier version came out at the FSE 2004 rump session.
• Two Remarks on Public Key Cryptology is a note on two ideas I floated at talks I gave in 1997-98, concerning forward-secure signatures and compatible weak keys. The first of these has inspired later research by others; the second gives a new attack on public key encryption.
• Two Practical and Provably Secure Block Ciphers: BEAR and LION shows how to construct a block cipher from a stream cipher and a hash function. We had already known how to construct stream ciphers and hash functions from block ciphers, and hash functions from stream ciphers; so this paper completed the set of elementary reductions. It also led to the `Dancing Bear' above.
• Tiger - A Fast New Hash Function defines a new hash function, which we designed following Hans Dobbertin's attack on MD4. This was designed to run extremely fast on the new 64-bit processors such as DEC Alpha and IA64, while still running reasonably quickly on existing hardware such as Intel 80486 and Pentium (the above link is to the Tiger home page, maintained in Haifa by Eli Biham; if the network is slow, see my UK mirrors of the Tiger paper, new and old reference implementations (the change fixes a padding bug) and S-box generation documents. There are also third-party crypto toolkits supporting Tiger, such as that from Bouncy Castle).
• Minding your p's and q's points out a number of things that can go wrong with the choice of modulus and generator in public key systems based on discrete log. It elucidated some of the previously classified reasoning behind the design of the US Digital Signature Algorithm, and appeared at Asiacrypt 96.
• Chameleon - A New Kind of Stream Cipher shows how to do traitor tracing using symmetric rather than public-key cryptology. The idea is to turn a stream cipher into one with reduced key diffusion, but without compromising security. A single broadcast ciphertext is decrypted to slightly different plaintexts by users with slightly different keys. This paper appeared at Fast Software Encryption in Haifa in January 1997.
• Searching for the Optimum Correlation Attack shows that nonlinear combining functions used in nonlinear filter generators can react with shifted copies of themselves in a way that opens up a new and powerful attack on many cipher systems. It appeared at the second workshop on fast software encryption.
• The Classification of Hash Functions showed that correlation freedom is strictly stronger than collision freedom, and shows that there are many pseudorandomness properties other than collision freedom which hash functions may need. It appeared at Cryptography and Coding 93.
• A Faster Attack on Certain Stream Ciphers shows how to break the multiplex shift register generator, which is used in satellite TV systems. I found a simple divide-and-conquer attack on this system in the mid 1980's, a discovery that got me `hooked' on cryptology. This paper is a refinement of that work.
• On Fibonacci Keystream Generators appeared at FSE3, and shows how to break `FISH', a stream cipher proposed by Siemens. It also proposes an improved cipher, `PIKE', based on the same general mechanisms.

• Soft Tempest: Hidden Data Transmission Using Electromagnetic Emanations must be one of the more unexpected and newsworthy papers I've published. It is well known that eavesdroppers can reconstruct video screen content from radio frequency emanations; up till now, such `Tempest attacks' were prevented by shielding, jammers and so on. Our innovation was a set of techniques that enable the software on a computer to control the electromagnetic radiation it emanates. This can be used for both attack and defence. To attack a system, malicious code can hide stolen information in the machine's Tempest emanations and optimise them for some combination of reception range, receiver cost and covertness. To defend a system, a screen driver can display sensitive information using fonts which minimise the energy of RF emanations. This technology is now fielded in PGP and eslewhere. You can download Tempest fonts from here.
• There is a followup paper on the costs and benefits of Soft Tempest in military environments, which appeared at NATO's 1999 RTO meeting on infosec, while an earlier version of our main paper, which received considerable publicity, is available here. Finally, there's some software you can use to play your MP3s over the radio here, a press article here and information on more recent optical tempest attacks here.
• Hollywood once hoped that copyright-marking systems would help control the copying of videos, music and computer games. This became high drama when a paper that showed how to break the DVD/SDMI copyright marking scheme was pulled by its authors from the Information Hiding 2001 workshop, following legal threats from Hollywood. In fact, the basic scheme - echo hiding - was among a number that we broke in 1997. The attack was reported in our paper Attacks on Copyright Marking Systems, which we published at Info Hiding 1998. We also wrote Information Hiding - A Survey, which appeared in Proc IEEE and is a good place to start if you're new to the field. For the policy aspects, you might read Pam Samuelson. There is much more about the technology on the web page of my former student Fabien Petitcolas.
• Another novel application of information hiding is the Steganographic File System. It will give you any file whose name and password you know, but if you do not know the correct password, you cannot even tell that a file of that name exists in the system! This is much stronger than conventional multilevel security, and its main function is to protect users against coercion. Two of our students implemented SFS for Linux: a paper describing the details is here, while the code is available here. This functionality has since appeared in a number of crypto products.
• The threat by some governments to ban cryptography has led to a surge of interest in steganography - the art of hiding messages in other messages. Our paper On The Limits of Steganography explores what can and can't be done; it appeared in a special issue of IEEE JSAC. It developed from an earlier paper, Stretching the Limits of Steganography, which appeared at the first international workshop on Information Hiding in 1996. I also started a bibliography of the subject which is now maintained by Fabien Petitcolas.
• The Newton Channel settles a conjecture of Simmons by exhibiting a high bandwidth subliminal channel in the ElGamal signature scheme. It appeared at Info Hiding 96.

Civil servants started pushing for online access to everyone's records in 1992 and I got involved in 1995, when I started consulting for the British Medical Association on the safety and privacy of clinical information systems. Back then, the police were given access to all drug prescriptions in the UK, after the government argued that they needed it to catch the occasional doctor who misprescribed heroin. The police got their data, they didn't catch Harold Shipman, and no-one was held accountable.

The NHS slogan in 1995 was `a unified electronic patient record, accessible to all in the NHS'. The slogan has changed several times, but the goal remains the same. The Health and Social Care (Community Health and Standards) Act allowed the Government access to all medical records in the UK, for the purposes of `Health Improvement'. It removed many of the patient privacy safeguards in previous legislation. In addition, the new contract offered to GPs since 2003 moves ownership of family doctor computers to Primary Care Trusts (that's health authorities, in oldspeak). There was a token consultation on confidentiality; the Foundation for Information Policy Research, which I chair, published a response to it (which was of course ignored).

The last time people pointed out that NHS administrators were helping themselves illegally to confidential personal health information, Parliament passed some regulations on patient privacy to legalise those questionable practices that had been brought to public attention. For example, the regulations compel doctors to give the government copies of all records relating to infectious disease and cancer. The regulations were made under an Act that was rushed through in the shadow of the 2001 election and that gives ministers broad powers to nationalise personal health information. For the background to that Act, see an editorial from the British Medical Journal, a discussion paper on the problems that the bill could cause for researchers, and an impact analysis commissioned by the Nuffield Trust. Ministers claimed the records were needed for cancer registries: yet cancer researchers in many other countries work with anonymised data (see papers on German cancer registries here and here, and the website of the Canadian Privacy Commissioner.) There was contemporary press coverage in the Observer, the New Statesman, and The Register; and Hansard reports the Parliamentary debate on the original bill in the Commons and the Lords.

In the end, perhaps only a European law challenge can halt the slide toward surveillance. The regulations appear to breach the Declaration of Helsinki on ethical principles for medical research, and contravene the Council of Europe recommendation no R(97)5 on the protection of medical data, to which Britain is a signatory. There is a list of some more of the problems here, and a letter we wrote to the BMJ here.

Some relevant papers of my own follow. They are mostly from the 1995-6 period, when the government last tried to centralise all medical records - and we saw them off.

• Security in Clinical Information Systems was published by the British Medical Association in January 1996. It sets out rules that can be used to uphold the principle of patient consent independently of the details of specific systems. It was the medical profession's initial response to the safety and privacy problems posed by centralised NHS computer systems.
• An Update on the BMA Security Policy appeared in June 1996 and tells the story of the struggle between the BMA and the government, including the origins and development of the BMA security policy and guidelines.
• There are comments made at NISSC 98 on the healthcare protection profiles being developed by NIST for the DHHS to use in regulating health information systems privacy. The protection profiles make a number of mistaken assumptions about the threats to medical systems and of the kind of protection mechanisms that are appropriate.
• Remarks on the Caldicott Report raises a number of issues about policy as it was settled in the late 1990s. The Caldicott Committee was set up by the Major government to kick the medical privacy issue into touch until after the 1997 election. Its members failed to understand that medical records from which the names have been removed, but where NHS numbers remain, are not really anonymous - as large numbers of people in the NHS can map names to numbers (and need to do this in order to do their jobs).
• Information technology in medical practice: safety and privacy lessons from the United Kingdom provided an overview of the safety and privacy problems we encountered in UK healthcare computing in the mid-90s for readers of the Australian Medical Journal.
• The DeCODE Proposal for an Icelandic Health Database analyses a proposal to collect all Icelanders' medical records into a single database. I evaluated this for the Icelandic Medical Association and concluded that the proposed security wouldn't work. The company running it has since hit financial problems but the ethical issues remain, and Iceland's Supreme Court recently allowed a woman to block access to her father's records because of the information they may reveal about her. (These issues may recur in the UK with the proposed Biobank database.) I also wrote an analysis of security targets prepared under the Common Criteria for the evaluation of this database. For more, see BMJ correspondence, the Icelandic doctors opposing the database, and an article by Einar Arnason.
• Clinical System Security - Interim Guidelines appeared in the British Medical Journal on 13th January 1996. It advises healthcare professionals on prudent security measures for clinical data. The most common threat is that private investigators use false-pretext telephone calls to elicit personal health information from assistant staff.
• A Security Policy Model for Clinical Information Systems appeared at the 1996 IEEE Symposium on Security and Privacy. It presents the BMA policy model to the computer security community in a format comparable to policies such as Bell-LaPadula and Clark-Wilson. It had some influence on later US health privacy legislation (the Kennedy-Kassebaum Bill, now HIPAA).
• NHS Wide Networking and Patient Confidentiality appeared in the British Medical Journal in July 1995 and set out some early objections to the government's health network proposals.
• Patient Confidentiality - At Risk from NHS Wide Networking went into somewhat more detail, particularly on the security policy aspects. It was presented at Health Care 96.
• Problems with the NHS Cryptography Strategy points out a number of errors in, and ethically unacceptable consequences of, a report on cryptography produced for the Department of Health. These comments formed the BMA's response to that report.
• I recently wrote a report for the National Audit Office on the health IT expenditure, strategies and goals of the UK and a number of other developed countries. This showed that the NHS National Program for IT is in many ways an outlier, and high-risk.
• I am one of the authors of a recent report on the safety and privacy of children's databases. This report was done for the UK Information Commissioner; it concluded that government plans to link up most of the public-sector databases that hold information on children are misguided. The proposed systems will be both unsafe and illegal. This report got a lot of publicity.

Two health IT papers by colleagues deserve special mention. Privacy in clinical information systems in secondary care describes a hospital system implementing something close to the BMA security policy (it is described in more detail in a special issue of the Health Informatics Journal, v 4 nos 3-4, Dec 1998, which I edited). Second, Protecting Doctors' Identity in Drug Prescription Analysis describes a system designed to de-identify prescription data for commercial use; although de-identification usually does not protect patient privacy very well, there are exceptions, such as here. This system led to a court case, in which the government tried to stop its owner promoting it - as it would have competed with their (less privacy-friendly) offerings. The government lost: the Court of Appeal decided that personal health information can be used for research without patient consent, so long as the de-identification is done competently.

A first-class collection of links to papers on the protection of de-identified data is maintained by the American Statistical Association. Bill Lowrance wrote a good survey for the US Department of Health and Human Services of the potential for using de-identified data to protect patient privacy in medical research, while a report by the US General Accounting Office shows how de-identified records are handled much better by Medicare than by the NHS. For information on what's happening in the German speaking world, see Andreas von Heydwolff's web site and Gerrit Bleumer's European project links. Resources on what's happening in the USA - where medical privacy is a very live issue - include many NGOs: Patient Privacy Rights, EPIC, the Privacy Rights Clearinghouse, the Medical Privacy Coalition, the Citizens' Council on Health Care, CPT, the Institute for Health Freedom. and Georgetown University's health privacy project (which has a comprehensive survey of US health privacy laws). Other resources include a report from the US National Academy of Sciences entitled For the Record: Protecting Electronic Health Information and a report by the US Office of Technology Assessment.

I chair the Foundation for Information Policy Research, which I helped set up in 1998. This body is concerned with promoting research and educating the public in such topics as the interaction between computing and the law, and the social effects of IT. We are not a lobby group; our enemy is ignorance rather than the government of the day, and one of our main activities is providing accurate and neutral briefing for politicians and members of the press. Here's an overview of the issues as we saw them in 1999; some highlights of our work follow.

• Key Escrow: My first foray into policy, in 1995, was Crypto in Europe - Markets, Law and Policy which surveyed the uses of cryptography in Europe and discussed the shortcomings of public policy. In it, I pointed out that law enforcement communications intelligence was mostly about traffic analysis and criminal communications security was mostly traffic security. This was considered heretical at the time but is now well known. The Risks of Key Recovery, Key Escrow, and Trusted Third-Party Encryption became perhaps the most widely cited publication on key escrow. It examines the technical risks, costs, and implications of deploying systems that would satisfy government wishes. It was originally presented as testimony to the US Senate, and then also to the Trade and Industry Committee of the UK House of Commons, together with a further piece I wrote, The Risks and Costs of UK Escrow Policy.
• The GCHQ Protocol and its Problems pointed out a number of serious defects in the protocol that the British government used to secure its electronic mail, and which it wanted everyone else to use too. This paper appeared at Eurocrypt 97 and it replies to GCHQ's response to an earlier version of our paper. Our analysis prevented the protocol from being widely adopted. The Global Trust Register is a book of the fingerprints of the world's most important public keys. It thus implements a top-level certification authority, but using paper and ink rather than electronics. If the DTI had pushed through mandatory licensing of cryptographic services, this book would have been banned in the UK. At a critical point in the lobbying, it enabled me to visit Culture Secretary Chris Smith and ask why his government wanted to ban my book. This got crypto policy referred to Cabinet when otherwise it would have been snuck through by the civil servants.
• This work on key escrow and related topics led up to a campaign that FIPR ran to limit the scope of the Regulation of Investigatory Powers Act. Originally this would have allowed the police to obtain, without warrant, a complete history of everyone's web browsing activity (under the rubric of `communications data'); an amendment FIPR got through the Lords limited this to the identity of the machines involved in a communication, rather than the actual web pages.
• E-Commerce: FIPR also brought together legal and computing experts to deconstruct the fashionable late-1990s notion that `digital certificates' would solve all the problems of e-commerce and e-government. The mandatory reading for anyone inclined to believe PKI salesmen's claims is Electronic Commerce - Who Carries the Risk of Fraud?. Other work in this thread include FIPR's responses to consultations on smartcards, the electronic signature directive and the ecommerce bill. Much of what we wrote has direct relevance today - to ID cards, to Trusted Computing and to debates on liability for ATM fraud and phishing.
• Terrorism: A page with Comments on Terrorism explains why many of the measures that various people have been trying to sell since the 11th September attacks are unlikely to work as promised. Much subsequent policy work has been made harder by assorted salesmen, centralisers, rent-seekers and chancers talking about terror; I recently testified against police attempts to increase pre-charge detention to ninety days with the implausible claim that they needed more time to decrypt seized data. We must constantly push back on the scaremongers.
• Export Control: In 2001-02, FIPR persuaded the Lords to amend the Export Control Bill. This bill was designed to give ministers the power to license intangible exports. It was the result of US lobbying of Tony Blair in 1997; back then, UK crypto researchers could put source code on our web pages while our US colleagues weren't allowed to. In its original form, its provisions were so broad that it would have given ministers the power of pre-publication review of scientific papers. We defeated the Government in the House of Lords by 150-108, following a hard campaign - see press coverage in the BBC, the New Scientist, the Guardian and the Economist, and an article on free speech I wrote for IEEE Computing. But the best quote I have is also the earliest. The first book written on cryptology in English, by Bishop John Wilkins in 1641, remarked that `If all those useful Inventions that are liable to abuse, should therefore be concealed, there is not any Art or Science which might be lawfully profest'
• This issue revived in 2003, with a government attempt to wrest back using regulations much of what they conceded in parliament. FIPR fought back and extracted assurances from Lord Sainsbury about the interpretation of regulations made under the Act. This may seem technical, but is important for British science and academic freedom. Without our campaign, much scientific collaboration would have become technically illegal, leaving scientists open to arbitrary harrassment. Much credit goes to the Conservative frontbencher Doreen Miller, Liberal Democrat frontbencher Margaret Sharp, and the then President of the Royal Society Bob May, who marshalled the crossbenchers in the Lords. We are very grateful to them for their efforts.
• Trusted Computing was a focus in 2002-03. I wrote a Trusted Computing FAQ that was very widely read, followed by a study of the competition policy aspects of this technology. This led inter alia to a symposium organised by the German government which in turn pushed the Trusted Computing Group into incorporating, admitting small companies, and issuing implementation guidelines. The next act in this drama awaits the launch of Windows Vista.
• IP Enforcement: Our top priority in 2003-04 was the EU IPR enforcement directive, which has been succinctly described as DMCA on steroids and also criticised by a number of distinguished lawyers. Our lobbying helped secure some positive amendments - notably, removing criminal sanctions and legal protection for devices such as RFID tags. Here are further criticisms of the directive by AEL. This law was supported by Microsoft, since convicted of anticompetitive behaviour; the music industry and the owners of luxury brands such as Yves Saint Laurent, while it was opposed by phone companies, supermarkets, smaller software firms and the free software community. The press was sceptical - in Britain, France and even America. The issue is even linked to a boycott of Gillette. There is more on my blog.
• In 2004 FIPR brought together NGOs from all over Europe to establish a common position on intellectual property. We've followed this up from time to time; recently I gave evidence to the Gowers Review of IP and a parliamentary committee on DRM.
• Identity Cards were a clever political ploy; they divided the Conservatives in 2004-5, setting the authoritarian leader Michael Howard against the libertarian majority in his shadow cabinet. But they are not good security engineering. I testified to the Home Affairs committee in 2004 that they would not work as advertised, and contributed to the LSE Report that spelled this out in detail. I'd produced numerous previous pieces in response to government identity consultations, on aspects such as smartcards and PKI. There's more in my book (ch. 6). Why are ministers and officials incapable of listening to scientific advice?
• Internet Censorship is a growing problem, and not just in developing countries. In 1995, I tried to forestall it by invneting the Eternity Service (a precursor of later file-sharing systems). But despite the technical difficulties and collateral costs of content filtering, governments aren't giving up. I recently became a principal investgator for the OpenNet Initiative which monitors Internet filtering worldwide.

My pro-bono work also includes sitting on Council, our University's governing body. I stood for election because I was concerned about the erosion of academic freedom under the previous administration. See, for example a truly shocking speech by Mike Clark at a recent discussion on IPR. Mike tells how our administration promised a research sponsor that he would submit all his relevant papers to them for prior review - without even asking him! It was to prevent abuses like this that we founded the Campaign for Cambridge Freedoms, whose goal was to defeat a proposal by the former Vice Chancellor that most of the intellectual property generated by faculty members - from patents on bright ideas to books written up from lecture notes - would belong to the university rather than to the person who created them. If this had passed, Cambridge would have swapped one of the most liberal rules on intellectual property of any British university, for one of the most oppressive anywhere. Over almost four years of campaigning we managed to draw many of the teeth of this proposal.

A recent vote approved a policy in which academics keep copyright but the University gets 15% of patent royalties. The policy is howerer defective in many ways: for example, it allows the University to do IPR deals without the consent of affected staff and students. The authorities have undertaken to introduce amendments.

Finally, here is my PGP key. If I revoke this key, I will always be willing to explain why I have done so provided that the giving of such an explanation is lawful. (For more, see FIPR.)

Security engineering is about building systems to remain dependable in the face of malice, error or mischance. As a discipline, it focuses on the tools, processes and methods needed to design, implement and test complete systems, and to adapt existing systems as their environment evolves. My book has become the standard textbook and reference since it was published in 2001.

Security engineering is not just concerned with `infrastructure' matters such as firewalls and PKI. It's also about specific applications, such as banking and medical record-keeping, and about embedded systems such as automatic teller machines and burglar alarms. It's usually done badly: it often takes several attempts to get a design right. It is also hard to learn: although there were good books on a number of the component technologies, such as cryptography and operating systems security, there was little about how to use them effectively, and even less about how to make them work together. It's hardly surprising that most systems don't fail because the mechanisms are weak, but because they're used wrong.

My book was an attempt to help the working engineer to do better. As well as the basic science, it contains details of many typical applications - and lot of case histories of how their protection mechanisms failed. It contains a fair amount of new material, as well as accounts of a number of technologies which aren't well described in the accessible literature. Writing it was also pivotal in founding the now-flourishing field of information security economics: I realised that the critical narrative had to do with incentives and organisation at least as often as with ciphers and access control. This led me to spend a fair proportion of my research time since on the interface between security and the social sciences.

More ...

I don't execute programs sent by strangers without good reason. So I don't read attachments in formats such as Word, unless by prior arrangement. I also discard html-only emails, as most of them are spam; and emails asking for `summer research positions' or `internships', which we don't do.

If you're contacting me about coming to Cambridge to do a PhD, please read the relevant web pages first.