New Paradigm for Practical Cryptosystems without Random Oracles
Tatsuaki Okamoto · NTT technical review · 2008
This paper introduces a new paradigm for making various types of cryptographic primitives such as authenticated key exchange and key encapsulation without random oracles under three assumptions: the decisional Diffie-Hellman assumption, target collision resistant hash functions, and a class of pseudorandom functions.It describes a new two-pass authenticated key exchange (AKE) protocol (based on the public key infrastructure model) that is comparable in efficiency to the most efficient of the existing protocols and secure (under these assumptions), whereas existing efficient two-pass AKE protocols are secure in the random oracle model.This protocol is shown to be secure in the (currently) strongest security definition, the extended Canetti-Krawczyk (eCK) security definition.This paper also describes a key encapsulation mechanism (KEM) that is secure against adaptive chosen ciphertext attacks (i.e., CCAsecure) under these assumptions and almost as efficient as the Kurosawa-Desmedt KEM.The schemes presented this paper are validity-check-free, which implies that combining them with validity-check-free symmetric encryption (data encryption mechanism) will yield validity-check-free (e.g., free of message authentication code) CCA-secure hybrid encryption.