Fully, (Almost) Tightly Secure IBE and Dual System Groups

We present the first fully secure Identity-Based Encryption scheme (IBE) from the standard assumptions where the security loss depends only on the security parameter and is independent of the number of secret key queries. This partially answers an open problem posed by Waters (Eurocrypt 2005). Our construction combines the Waters' dual system encryption methodology (Crypto 2009) with the Naor-Reingold pseudo-random function (J. ACM, 2004) in a novel way. The security of our scheme relies on the DLIN assumption in prime-order groups. Along the way, we introduce a novel notion of dual system groups and a new randomization and parameter-hiding technique for prime-order bilinear groups.