Topics in Cryptology – CT-RSA 2013

Volume 7779 of the series Lecture Notes in Computer Science pp 310-325

The k-BDH Assumption Family: Bilinear Map Cryptography from Progressively Weaker Assumptions

  • Karyn BensonAffiliated withUniversity of California
  • , Hovav ShachamAffiliated withUniversity of California
  • , Brent WatersAffiliated withUniversity of Texas at Austin

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Over the past decade bilinear maps have been used to build a large variety of cryptosystems. In addition to new functionality, we have concurrently seen the emergence of many strong assumptions. In this work, we explore how to build bilinear map cryptosystems under progressively weaker assumptions.

We propose k-BDH, a new family of progressively weaker assumptions that generalizes the decisional bilinear Diffie-Hellman (DBDH) assumption. We give evidence in the generic group model that each assumption in our family is strictly weaker than the assumptions before it. DBDH has been used for proving many schemes secure, notably identity-based and functional encryption schemes; we expect that our k-BDH will lead to generalizations of many such schemes.

To illustrate the usefulness of our k-BDH family, we construct a family of selectively secure Identity-Based Encryption (IBE) systems based on it. Our system can be viewed as a generalization of the Boneh-Boyen IBE, however, the construction and proof require new ideas to fit the family. Our methods can be extended to produce hierarchical IBEs and CCA security; and give a fully secure variant. In addition, we discuss the opportunities and challenges of building new systems under our weaker assumption family.