New approach to combine secret keys for post-quantum (Pq) transition

Abstract

Many companies are working to build a powerful quantum computer. Once quantum computer with large qubits is reality, asymmetric-key cryptosystem will be vulnerable for Shor’s algorithm. The transition from one cryptosystem to another is very slow process and consumes many years. National Institute of Standards and Technology (NIST) is working on standardization of post-quantum cryptographic (PQC) algorithms. Security of current PQC algorithms cannot be fully verified today. So, in coming years we need to rely on both traditional algorithms and PQC algorithms. Hybrid mode consisting of one traditional algorithm and one post quantum algorithm is a best solution for smooth migration to quantum-safe cryptosystem. For key exchange, it means using two or more key exchange encapsulation algorithms for generating session key [Meher and Midhunchakkaravarthy (2019)]. For authentication, it means using two or more digital signature algorithms [Meher and Midhunchakkaravarthy (2019)]. There are number of approaches to combine secret key from traditional algorithm and PQC algorithm to make key encapsulation mechanism quantum-proof. In the paper we propose a new approach of using secret master key generated from one of the KEM algorithm as a salt for hashbased key derivation function (HKDF) to drive session keys from secret master key generated from another KEM algorithm.