## Cryptology ePrint Archive: Report 2013/604

Modelling Time, or A Step Towards Reduction-based Security Proofs for OTP and Kerberos

Jörg Schwenk

Abstract: The notion of time plays an important role in many practically deployed cryptographic protocols, ranging from One-Time-Password (OTP) tokens to the Kerberos protocol. However, time is difficult to model in a Turing machine environment.

We propose the first such model, where time is modelled as a global counter T . We argue that this model closely matches several implementations of time in computer environments. The usefulness of the model is shown by giving complexity-theoretic security proofs for OTP protocols, HMQV-like one-round AKE protocols, and a variant of the basic Kerberos building block.

Category / Keywords: cryptographic protocols / BR model, timestamp, OTP, one-round AKE, Kerberos