Efficient and scalable aggregate signcryption scheme based on multi-trapdoor hash functions

Secure communication in computer network systems, like clouds, requires mechanisms that, at the very least, provide confidentiality, integrity and authentication. Signcryption is one such mechanism to simultaneously provide all three features by producing encrypted and digitally signed messages using a logically single operation that is more efficient than the cumulative cost of encrypting and signing. To further improve scalability and efficiency when multiple communicating parties are involved, individual signcryptext can be aggregated into a single aggregate signcryptext. Aggregation of signcryptexts provides significant savings in bandwidth, since the resulting aggregate signcryptext is typically shorter that the combined signcryptexts, and savings in computation since unsigncryption of the aggregate signcryptext typically requires fewer operations that unsigncrypting individual signcryptexts. Unfortunately, most existing schemes do not scale well in terms of bandwidth with increasing number of entities, or signcrypters, that are generating the signcryptions . This paper introduces the first aggregate signcryption scheme in literature that produces constant-sized signcryptexts regardless of the number of signcrypters. The scheme is built using the recently proposed concept of multi-trapdoor hash functions that allows multiple entities to compute a collision with a given hash value, and decomposable encryption that allows compressing ciphertexts in a manner that allows efficient retrieval of each individual plaintext. We also provide a high-level correctness, security and performance evaluation of the proposed scheme. The security of the proposed scheme is based on the well know discrete log and decisional Diffie-Hellman assumptions, and the performance compares favorably to all other existing schemes.