Generic Forward-Secure Key Agreement Without Signatures

Abstract

We present a generic, yet simple and efficient transformation to obtain a forward secure authenticated key exchange protocol from a two-move passively secure unauthenticated key agreement scheme (such as standard Diffie–Hellman or Frodo or NewHope). Our construction requires only an IND-CCA public key encryption scheme (such as RSA-OAEP or a method based on ring-LWE), and a message authentication code. Particularly relevant in the context of the state-of-the-art of postquantum secure primitives, we avoid the use of digital signature schemes: practical candidate post-quantum signature schemes are less accepted (and require more bandwidth) than candidate post-quantum public key encryption schemes. An additional feature of our proposal is that it helps avoid the bad practice of using long term keys certified for encryption to produce digital signatures. We prove the security of our transformation in the random oracle model.