Composition of Password-based Protocols

Céline Chevalier (1) , Stéphanie Delaune (1) , Steve Kremer (2) , Mark D. Ryan (3)

1 LSV - Laboratoire Spécification et Vérification [Cachan]
2 CASSIS - Combination of approaches to the security of infinite states systems
3 School of Computer Science [Birmingham]

Formal and symbolic techniques are extremely useful for modelling and analysing security protocols. They have helped to improve our understanding of such protocols, allowed us to discover aws, and they also provide support for protocol design. However, such analyses usually consider that the protocol is executed in isolation or assume a bounded number of protocol sessions. Hence, no security guarantee is provided when the protocol is executed in a more complex environment.\par In this paper, we study whether password protocols can be safely composed, even when a same password is reused. More precisely, we 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. Our result provides an effective strategy to design secure password protocols: (i) design a protocol intended to be secure for one protocol session; (ii) apply our transformation and obtain a protocol which is secure for an unbounded number of sessions. Our technique also applies to compose different password protocols allowing us to obtain both inter-protocol and inter-session composition.

Domaines: Cryptographie et sécurité [cs.CR]

Céline Chevalier, Stéphanie Delaune, Steve Kremer, Mark D. Ryan. Composition of Password-based Protocols. Formal Methods in System Design, 2013, 43 (3), pp.369-413. ⟨10.1007/s10703-013-0184-6⟩. ⟨hal-00878640⟩