Cryptology ePrint Archive: Report 2002/060

A Forward-Secure Public-Key Encryption Scheme

Jonathan Katz

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.

Category / Keywords: public-key cryptography / forward-security, encryption

Date: received 24 May 2002, last revised 2 May 2003

Contact author: jkatz at cs umd edu

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation

Note: Superseded by the version appearing in Eurocrypt 2003 (a full version of which is available at

Version: 20030502:193347 (All versions of this report)

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