Tom Chothia

Email:tomc at
Laboratoire d'informatique (LIX)
Ecole polytechnique

I have moved

The page is out of date. My new page can be found here


My research is based on using process calculi to design and reason about secure distributed computing. Some current pieces of work include:
  • Anonymity I am interested in the design and theory of anonymous systems. I have a page on anonymous file-sharing here.

  • Guessing attacks in the pi-calculus with a Computational Justification.

    This work presents an extension of the pi-calculus that can reason about brute force and guessing attacks. We relate new name declarations in the pi-calculus with random sampling in the computational model of security. The scope of a new name can then be expanded at a comparable cost as it would take to guess the randomly sampled value in the computational setting. We argue the correctness of this calculus by relating it to the computational model of security. We show that if the cost of an attack in the calculus is less than exponential in a security parameter, then there exists a polynomial time Turing machine that can defeat the process with non-negligibility probability. On the other hand, if there is no sub-exponential cost attack, then the process is just as safe as its spi-calculus counterpart, and so the use of guessable names does not help the attacker.

    I have two draft paper on this work a
    short paper (15 pages llncs style) and a long paper (15 pages IEEE style). Comments and suggestions are welcome. N.B. this paper is highly subject to change, the current version is dated 4/4/2005.
    I also have power point slides from a talk I have given about this work at Imperial, ACI ROSSIGNOL, LIX and VERIMAG.

  • The Jeddak Language for Distributed Access Control.

    This language is an extension of Java which allows specifying policies, compile-time checking of software against policies, and run-time auditing to enforce accountability. It is based on the Key Based Distributed Label Model which is outline in: "Type-Based Distributed Access Control", Tom Chothia, Dominic Duggan and Jan Vitek, CSFW 03 In which a type system is presented that combines a weak form of information flow control, termed distributed access control in the paper, with typed cryptographic operations. The motivation is to have a type system that ensures access control while giving the application the responsibility to secure network communications, and to do this safely. The notion of declassification certificates is introduced to support the declassification of encrypted data.
    I also have power point slides from a talk I have given about this work at CSFW,INRIA,LFCS, among other places.

  • Papers

    [0] A Survey of Anonymous Peer-to-Peer File-Sharing. Tom Chothia and Konstantinos Chatzikokolakis. To appear at IFIP International Symposium on Network-Centric Ubiquitous Systems (NCUS 2005) .pdf
    [1] Capability-Passing Processes. Tom Chothia and Dominic Duggan. In The 4th International Workshop on Foundations of Coordination Languages and Software Architectures (FOCLASA 2005)
    [A long version with proofs bib | .pdf ]
    [2] Typed-based Access Control vs. Untyped Attackers. Tom Chothia and Dominic Duggan. In The 3rd Workshop on Formal Aspects in Security and Trust (FAST 2005)
    [ bib | .pdf ]
    [3] Trusting the Network. Tom Chothia, Dominic Duggan and Ye Wu. In Workshop on Foundations of Computer Security (FCS 2005)
    [ bib | .pdf ]
    [4] Metrics for action-labelled quantitative transition systems. Yuxin Deng, Tom Chothia, Catuscia Palamidessi, and Jun Pang. In 3rd Workshop on Quantitative Aspects of Programming Languages (QAPL'05), volume Electronic Notes in Theoretical Computer Science. Elsevier, 2005.
    [ bib | .pdf ]
    [5] Abstractions for fault-tolerant global computing. Tom Chothia and Dominic Duggan. Abstractions for fault-tolerant global computing. Theoretical Computer Science, 322(3), 2004.
    [ bib | .ps ]
    [6] Principals, policies and keys in a secure distributed programming language. Tom Chothia, Dominic Duggan, and Jan Vitek. In Foundations of Computer Security - FCS'04, Turku, Finland, July 2004.
    [ bib | .ps ]
    [7] Type-Based Distributed Access Control. Tom Chothia, Dominic Duggan, and Jan Vitek. In 16th IEEE Computer Security Foundations Workshop (CSFW-16 2003), pages 170-186. IEEE Computer Society, 2003.
    [ bib | .pdf ]
    [8] An Architecture for Secure Fault-Tolerant Global Applications. Tom Chothia and Dominic Duggan. In Workshop on Principles of Dependable Systems, 2003.
    [ bib | .pdf ]
    [9] The Local Area pi-Calculus. Tom Chothia. PhD thesis, Edinburgh University, 2002.
    [ bib | .ps ]
    [10] Gaze: a generic framework for the integration of gene prediction data by dynamic programming. K.L. Howe, T. Chothia, and R. Durbin. Genome Research, 12(9):1418-1427, 2002.
    [ bib | .pdf ]
    [11] Encoding distributed areas and local communication into the pi-calculus. Tom Chothia and Ian Stark. In Expressiveness in Concurrency, EXPRESS, 2001.
    [ bib | .ps ]
    [12] A distributed calculus with local areas of communication. Tom Chothia and Ian Stark. In High Level Concurrent Languages, 2000.
    [ bib | .pdf ]

    Past Work

  • I did a Post Doc. at Stevens Institute of Technology. Where my work included models of fault tolerant computing.
  • I did my PhD at the University of Edinburgh. The ability to call local resources with uniform commands is fundamental to mobile computation. This led me to investigate a notion of binding a channel so that it has a number of mutually exclusive local areas. Communication on the channel is then allowed inside these areas but not between then. I have developed a boxed pi-calculus called the local area calculus that captures this notion.
  • I worked on a gene finder for the Human genome project . The results are published as:

  • K.L. Howe, T. Chothia and R. Durbin. GAZE: a generic framework for the integration of gene prediction data by dynamic programming (pdf). Genome Research 2002, vol. 12(9) pages 1418-1427.

  • and details can be found here . This work also lead to me being one of the 1000 plus, listed authors of:

  • International Human Genome Sequencing Consortium. 2001. Initial sequencing and analysis of the human genome. Nature 409, 6822, 860--921.