Hybrid Cryptography

Abstract

This paper examines the methods in which the ideas behind a KEM--DEM hybrid encryption scheme can be extended to other types of asymmetric primitives, particularly to signcryption schemes. The central principle is a keyed symmetric algorithm can be used to provide a security service for in an asymmetric algorithm provided that that symmetric primitive is under the control of the asymmetric part of the cipher (say, if asymmetric techniques are used to generate the key that the symmetric primitive uses). This theory is applied to signcryption schemes with outsider security and an efficient, provably secure scheme, termed ECISS-KEM, is proposed. The theory is also applied to signature schemes, where it is shown that efficient hybrid signature schemes can never exist, and to signcryption schemes with insider security, where it is shown that several existing schemes can be considered hybrid signcryption schemes