Section: New Results

Composition results

Participant : Stéphanie Delaune.

Formal methods have proved their usefulness for analysing the security of protocols. However, protocols are often analysed in isolation, and this is well-known to be not sufficient as soon as the protocols share some keys.

Stéphanie Delaune, in collaboration with Céline Chevalier, Steve Kremer, and Mark Ryan, study whether password protocols can be safely composed, even when a same password is reused. More precisely, they present a transformation which maps a password protocol that is secure for a single protocol session (a decidable problem) to a protocol that is secure for an unbounded number of sessions. Their result provides an effective strategy to design secure password protocols: (i) design a protocol intended to be secure for one protocol session; (ii) apply their transformation and obtain a protocol which is secure for an unbounded number of sessions. Their technique also applies to compose different password protocols allowing one to obtain both inter-protocol and inter-session composition. This work was published as:

• C. Chevalier, S. Delaune, S. Kremer and M. Ryan. Composition of Password-based Protocols. Formal Methods in System Design 43(3), pages 369-413, 2013.