sHMQV: An Efficient Key Exchange Protocol for Power-Limited Devices

In this paper we focus on designing authenticated key exchange protocols for practical scenarios where the party consists of a powerful but untrusted host (e.g., PC, mobile phone, etc) and a power-limited but trusted device (e.g., Trusted Platform Module, Mobile Trusted Module, Smart Card, etc). HMQV and (s,r) OAKE1 protocols are the state-of-the-art in the integrity of security and efficiency. However, we find that they are not suitable for the above scenarios as all (or part) of the online exponentiation computations must be performed in the power-limited trusted devices, which makes them inefficient for the deployment in practice. To overcome the above inefficiency, we propose a variant of HMQV protocol, denoted sHMQV, under some new design rationales which bring the following advantages: 1) eliminating the validation of the ephemeral public keys, which costs one exponentiation; 2) the power-limited trusted device only performs one exponentiation, which can be pre-computed offline; 3) all the online exponentiation computations can be performed in the powerful host. The above advantages make sHMQV enjoy better performance than HMQV and (s, r) OAKE, especially when deployed in the scenarios considered in this paper. We finally formally prove the security of sHMQV in the CK model.