Séminaire des équipes-projets

Non-Interactive CCA-Secure Threshold Cryptosystems with Adaptive Security: New Framework and Constructions

A 10h00, entrée libre.

  • Date : 19/01/2012
  • Lieu : École Normale Supérieure, Amphi Évariste Galois - NIR
  • Intervenants : Benoît Libert (UCL)
  • Organisateurs : Cascade

In threshold cryptography, private keys are divided into n shares, each one of which is given to a different server in order to avoid single points of failure. In the case of threshold public-key encryption, at least t out of n servers need to contribute to the decryption process. A threshold primitive is said robust if no coalition of t malicious servers can prevent remaining honest servers from successfully completing private key operations. So far, most practical non-interactive threshold cryptosystems, where no interactive conversation is required among decryption servers, were only proved secure against static corruptions. In the adaptive corruption scenario (where the adversary can corrupt servers at any time, based on its complete view), almost all existing robust threshold encryption schemes that also resist chosen-ciphertext attacks require some interaction in the decryption phase. In this work, we describe several constructions of adaptively secure, robust and fully non-interactive threshold cryptosystems with chosen-ciphertext security. These schemes stem from a new framework based on hash proof systems with publicly verifiable proofs. All instantiations rely on well-studied assumptions in bilinear groups.
 
 Joint work with Moti Yung

Mots-clés : Séminaire Équipe-projet CASCADE

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