Key Evolution Systems in Untrusted Update Environments

  • Authors:
  • Benoît Libert;Jean-Jacques Quisquater;Moti Yung

  • Affiliations:
  • UCL, Microelectronics Laboratory, Crypto Group, Belgium;UCL, Microelectronics Laboratory, Crypto Group, Belgium;Google Inc. and Columbia University, USA

  • Venue:
  • Information Security and Cryptology
  • Year:
  • 2009

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Abstract

Key-evolving protocols aim at limiting damages when an attacker obtains full access to the signer's storage. To simplify the integration of such mechanisms into standard security architectures, Boyen, Shacham, Shen and Waters suggested the construction of forward-secure signatures (FSS) that protect past periods after a break-in, with untrusted updates where private keys are additionally protected by a second factor (derived from a password). Key updates can be made on encrypted version of private keys so that passwords only come into play for signing messages. Boyen et al. described a pairing-based scheme in the standard model and also suggested the integration of untrusted updates in the Bellare-Miner forward-secure signature. They left open the problem of endowing other efficient FSS systems with the same second factor protection. We first address this problem and suggest generic ways to construct FSS schemes in untrusted update environments. In a second step, we extend the unprotected update model to other key-evolving systems such as forward-secure public key encryption and key-insulated cryptosystems. We then explain how some of the constructions that we proposed for forward-secure signatures can be adapted to these models.