Tag-KEM/DEM: A New Framework for Hybrid Encryption

Dr. Masayuki Abe (joint work with Rosario Gennaro and Kaoru Kurosawa)

NTT Japan

This paper presents a novel framework for generic construction of hybrid encryption schemes which produces more efficient schemes than before. A known framework introduced by Shoup combines a key encapsulation mechanism (KEM) and a data encryption mechanism (DEM). While it is sufficient to require both components to be secure against chosen ciphertext attacks, Kurosawa and Desmedt showed a particular example of KEM that is not CCA but can be securely combined with a specific type of CCA DEM yielding more efficient hybrid encryption scheme. There are also many efficient hybrid encryption schemes in various settings that do not fit to the framework. These facts serve as motivation to seek another framework that yields more efficient schemes.
We propose a new framework which we call Tag-KEM/DEM. It extends the notion of KEM and accepts much weaker DEM that is only secure against passive attacks. In addition to the potential efficiency of the resulting schemes, our framework will provide insightful explanation about existing schemes that do not fit to the previous framework. This could result in finding improvements for some schemes. Moreover, it allows immediate conversion from a class of threshold public-key encryption to a hybrid one without considerable overhead, which is not possible in the previous approach.

Short Bio: Masayuki Abe is a senior researcher in NTT Laboratories. He has been working in the cryptographic research croup since he joined to NTT in '92. His research interest includes cryptographic protocol design, zero-knowledge proofs, digital signatures, public-key encryption, multi-party computation, and privacy and anonymity issues.