A new publication : Lengths may break privacy — or how to check for equivalences with length

A new publication related to the development of APTE was added: Lengths may break privacy — or how to check for equivalences with length. This is a work done by Vincent Cheval, VĂ©ronique Cortier and Antoine Plet. It will be published in Proceedings of the 25th International Conference on Computer Aided Verification (CAV’13).

Abtract: Security protocols have been successfully analyzed using symbolic models, where messages are represented by terms and protocols by processes. Privacy properties like anonymity or untraceability are typically expressed as equivalence between processes. While some decision procedures have been proposed for automatically deciding process equivalence, all existing approaches abstract away the information an attacker may get when observing the length of messages.

In this paper, we study process equivalence with length tests. We first show that, in the static case, almost all existing decidability results (for static equivalence) can be extended to cope with length tests.
In the active case, we prove decidability of trace equivalence with length tests, for a bounded number of sessions and for standard primitives. Our result relies on a previous decidability result from Cheval et al (without length tests). Our procedure has been implemented and we have discovered a new flaw against privacy in the biometric passport protocol.

Current state of the implementation: The algorithm corresponding to the Theorem 2 was implemented in APTE v0.2alpha and sooner. It corresponds to the command “equivalence length” (see Tutorial). The algorithm corresponding to the Theorem 3 is yet to be implemented.