Séminaire de Cryptographie

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Benoit Libert

Efficient Intrusion-Resilient Signatures Without Random Oracle

Intrusion-resilient signatures are key-evolving protocols that extend the concepts of forward-secure and key-insulated signatures. As in the latter schemes, time is divided into distinct periods where private keys are periodically updated while public keys remain fixed. Private keys are stored in both a user and a base; signature operations are performed by the user while the base is involved in periodic updates. Such a system remains secure after arbitrarily many compromises of both modules as long as break-ins are not simultaneous. Besides, when they simultaneously occur within some time period, past periods remain safe. In this work, we propose the first intrusion-resilient signature in the standard model (i.e. without random oracles) which provides both constant-size (short) signatures and at most log-squared private storage in the number of time periods.