Multi-trapdoor hash functions and their applications in network security

We introduce the concept of a multi-trapdoor hashing scheme that allows multiple entities to compute a collision with a given hash value. Unlike previous proposals that use of multiple trapdoors to strengthen security of conventional trapdoor hash functions, the proposed use of multiple trapdoors in hash functions is motivated by potential applications in security schemes involving multiple participants. We present two such applications that include preliminary designs of aggregate signatures and sanitizable signatures with support for multiple sanitizers. We also present a discrete log-based instantiation of the proposed concept using a novel key-exposure free trapdoor hash function. Finally, we analyze the proposed instantiation in terms of its security and performance.