International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: A Forward-Secure Public-Key Encryption Scheme

Jonathan Katz
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Abstract: Cryptographic computations are often carried out on insecure devices for which the threat of key exposure represents a serious and realistic concern. In an effort to mitigate the damage caused by exposure of secret data stored on such devices, the paradigm of \emph{forward security} was introduced. In this model, secret keys are updated at regular intervals throughout the lifetime of the system; furthermore, exposure of a secret key corresponding to a given interval does not enable an adversary to ``break'' the system (in the appropriate sense) for any \emph{prior} time period. A number of constructions of forward-secure digital signature schemes and symmetric-key schemes are known. We present the first construction of a forward-secure public-key encryption scheme whose security is based on the bilinear Diffie-Hellman assumption in the random oracle model. Our scheme can be extended to achieve chosen-ciphertext security at minimal additional cost. The construction we give is quite efficient: all parameters of the scheme grow (at most) poly-logarithmically with the total number of time periods.
  title={A Forward-Secure Public-Key Encryption Scheme},
  booktitle={IACR Eprint archive},
  keywords={public-key cryptography / forward-security, encryption},
  note={ 12174 received 24 May 2002, last revised 2 May 2003},
  author={Jonathan Katz},