Secure Hybrid Encryption from Weakened Key Encapsulation

We put forward a new paradigm for building hybrid encryption schemes from constrained chosen-ciphertext secure (CCCA) key-encapsulation mechanisms (KEMs) plus authenticated symmetric encryption. Constrained chosen-ciphertext security is a new security notion for KEMs that we propose. CCCA has less demanding security requirements than standard chosen-ciphertext (CCA) security (since it requires the adversary to have a certain plaintextknowledge when making a decapsulation query) yet we can prove that CCCA is sufficient for secure hybrid encryption. Our notion is not only useful to express the Kurosawa-Desmedt public-key encryption nd its generalizations to hash-proof systems in an abstract KEM/DEM security framework. It also has a very constructive appeal, which we demonstrate with a new encryption scheme whose security relies on a class of intractability assumptions that we show (in the generic group model) strictly weaker than the Decision Diffie-Hellman (DDH) assumption. This appear...

• Type: Conference
• Year: 2007
• Where: CRYPTO
• Authors: Dennis Hofheinz, Eike Kiltz
• Keywords: CRYPTO 2007, Encryption Scheme, Hybrid Encryption, Security