Lossy trapdoor functions and their applications

Abstract

We propose a new general primitive called lossy trapdoor functions (lossy TDFs), and realize it under a variety of different number theoretic assumptions, including hardness of the decisional Diffie-Hellman (DDH) problem and the worst-case hardness of lattice problems. Using lossy TDFs, we develop a new approach for constructing several important cryptographic primitives, including (injective) trapdoor functions, collision-resistant hash functions, oblivious transfer, and chosen ciphertext-secure cryptosystems. All of the constructions are simple, efficient, and black-box. These results resolve some long-standing open problems in cryptography. They give the first known injective trapdoor functions based on problems not directly related to integer factorization, and provide the first known CCA-secure cryptosystem based solely on the worst-case complexity of lattice problems.