Annual Cryptology Conference

CRYPTO 2011: Advances in Cryptology – CRYPTO 2011 pp 543-560

Better Security for Deterministic Public-Key Encryption: The Auxiliary-Input Setting

  • Zvika Brakerski
  • Gil Segev
Conference paper

DOI: 10.1007/978-3-642-22792-9_31

Volume 6841 of the book series Lecture Notes in Computer Science (LNCS)


Deterministic public-key encryption, introduced by Bellare, Boldyreva, and O’Neill (CRYPTO ’07), provides an alternative to randomized public-key encryption in various scenarios where the latter exhibits inherent drawbacks. A deterministic encryption algorithm, however, cannot satisfy any meaningful notion of security when the plaintext is distributed over a small set. Bellare et al. addressed this difficulty by requiring semantic security to hold only when the plaintext has high min-entropy from the adversary’s point of view.

In many applications, however, an adversary may obtain auxiliary information that is related to the plaintext. Specifically, when deterministic encryption is used as a building block of a larger system, it is rather likely that plaintexts do not have high min-entropy from the adversary’s point of view. In such cases, the framework of Bellare et al. might fall short from providing robust security guarantees.

We formalize a framework for studying the security of deterministic public-key encryption schemes with respect to auxiliary inputs. Given the trivial requirement that the plaintext should not be efficiently recoverable from the auxiliary input, we focus on hard-to-invert auxiliary inputs. Within this framework, we propose two schemes: the first is based on the decisional Diffie-Hellman (and, more generally, on the d-linear) assumption, and the second is based on a rather general class of subgroup indistinguishability assumptions (including, in particular, quadratic residuosity and Paillier’s composite residuosity). Our schemes are secure with respect to any auxiliary input that is subexponentially hard to invert (assuming the standard hardness of the underlying computational assumptions). In addition, our first scheme is secure even in the multi-user setting where related plaintexts may be encrypted under multiple public keys. Constructing a scheme that is secure in the multi-user setting (even without considering auxiliary inputs) was identified by Bellare et al. as an important open problem.

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Copyright information

© International Association for Cryptologic Research 2011

Authors and Affiliations

  • Zvika Brakerski
    • 1
  • Gil Segev
    • 2
  1. 1.Department of Computer Science and Applied MathematicsWeizmann Institute of ScienceRehovotIsrael
  2. 2.Microsoft ResearchUSA