SPEAKER: Jung Hee Cheon TITLE: Trapdoor DL groups and their Applications AUTHORS: Jung Hee Cheon ABSTRACT: In this talk, we will discuss new developments concerning trapdoor DL groups and their instantiation in Z_N^*. At Eurocrypt'91, Maurer-Yacobi proposed a trapdoor DL group in Z_N^* where N=pq is a product of two primes and p-1 and q-1 are B-smooth. Without knowing the factorization of N, the DLP on Z_N^* takes O(B log N/log B) using the Pollard (p-1) method. However, given the factorization as a trapdoor, it takes only O(sqrt B log N/log B) time using the Pohlig-Hellman and Pollard rho methods. In this work, we show that DL groups with trapdoors can be made more practical via a recently developed memory-efficient DL algorithm with precomputation. We show the trade-off between the precomputation, the online computation and the memory usage. Further we discuss several applications of Trapdoor DL groups including ID-based encryption without pairings. Finally, on a more applied note we suggest some specific parameter settings and their implications. LINK: (Related Papers) 1) Paterson, Sriramkrishnan - "On the relations between non-interactive key distribution, identity-based encryption and trapdoor discrete log groups" http://dx.doi.org/10.1007/s10623-009-9278-y 2) Maurer, Yacobi - "Non-interactive Public-Key Cryptography" http://link.springer.de/link/service/series/0558/bibs/0547/05470498.htm