Paper 2007/288

Secure Hybrid Encryption from Weakened Key Encapsulation

Dennis Hofheinz and Eike Kiltz


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 plaintext-knowledge 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 scheme and 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 appears to be the first practical public-key encryption scheme in the literature from an algebraic assumption strictly weaker than DDH.

Available format(s)
Public-key cryptography
Publication info
Published elsewhere. A preliminary version of this paper appears in the proceedings of CRYPTO 2007. This is the full version.
Chosen-ciphertext securityweak security assumptionshybrid encryption
Contact author(s)
kiltz @ cwi nl
2007-08-07: received
Short URL
Creative Commons Attribution


      author = {Dennis Hofheinz and Eike Kiltz},
      title = {Secure Hybrid Encryption from Weakened Key Encapsulation},
      howpublished = {Cryptology ePrint Archive, Paper 2007/288},
      year = {2007},
      note = {\url{}},
      url = {}
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