The Dual Receiver Cryptosystem and Its Applications

摘要

We put forth the notion of a dual receiver cryptosystem and implement it based on bilinear pairings over certain elliptic curve groups. The cryptosystem is simple and efficient yet powerful, as it solves two problems of practical importance whose solutions have proven to be elusive before: (1) A provably secure "combined" public-key cryptosystem (with a single secret key per user in space-limited environment) where the key is used for both decryption and signing and where encryption can be escrowed and recovered, while the signature capability never leaves its owner. This is an open problem proposed by the work of Haber and Pinkas. (2) A puzzle is a method for rate-limiting remote users by forcing them to solve a computational task (the puzzle). Puzzles have been based on cryptographic challenges in the past, but the successful design of embedding a useful cryptographic task inside a puzzle, originally posed by Dwork and Naor, remained an open problem till today. We model and present "useful security puzzles" applicable in two scenarios: a secure fileserver, and an online transaction server (such as a webserver).