International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Chosen-Ciphertext Secure Key-Encapsulation Based on Gap Hashed Diffie-Hellman

Eike Kiltz
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Abstract: We propose a practical key encapsulation mechanism with a simple and intuitive design concept. Security against chosen-ciphertext attacks can be proved in the standard model under a new assumption, the Gap Hashed Diffie-Hellman (GHDH) assumption. The security reduction is tight and simple. Secure key encapsulation, combined with an appropriately secure symmetric encryption scheme, yields a hybrid public-key encryption scheme which is secure against chosen-ciphertext attacks. The implied encryption scheme is very efficient: compared to the previously most efficient scheme by Kurosawa and Desmedt [Crypto 2004] it has 128 bits shorter ciphertexts, between 25-50% shorter public/secret keys, and it is slightly more efficient in terms of encryption/decryption speed. Furthermore, our scheme enjoys (the option of) public verifiability of the ciphertexts and it inherits all practical advantages of secure hybrid encryption.
  title={Chosen-Ciphertext Secure Key-Encapsulation Based on Gap Hashed Diffie-Hellman},
  booktitle={IACR Eprint archive},
  keywords={public-key cryptography / Chosen-ciphertext security, Public-key encryption, key encapsulation},
  note={Preliminary version in PKC 2007. This is the full version. 13558 received 5 Feb 2007, last revised 14 Feb 2007},
  author={Eike Kiltz},