Abstract

At Eurocrypt 1998, Blaze, Bleumer and Strauss (BBS) presented a new primitive called proxy re-
encryption. This new primitive allows semi trusted proxy to convert a ciphertext for Alice into a
ciphertext for Bob without underlying message. Till now all the identity based proxy re-encryption
schemes are based on the number theoretic assumptions like prime factorization, discrete logarithm
problem etc. In this paper we propose a lattice based identity based proxy re-encryption scheme
in the random oracle model for the single bit as well as for the multi-bit. Both of our schemes are
anonymous, bidirectional and multi use. In these schemes, we have used Micciancio and Peikert’s
strong trapdoor [20] and this strong trapdoor is shown to be very efficient [6].