Signcryption in Hierarchical Identity Based Cryptosystem

In many situations we want to enjoy confidentiality, authenticity and non-repudiation of message simultaneously. One approach to achieve this objective is to “sign-then-encrypt” the message, or we can employ special cryptographic scheme like signcryption. Two open problems about identity-based (ID-based) signcryption were proposed in [16]. The first one is to devise an efficient forward-secure signcryption scheme with public verifiability and public ciphertext authenticity, which is promptly closed by [10]. Another one which still remains open is to devise a hierarchical ID-based signcryption scheme that allows the user to receive signcrypted messages from sender who is under another sub-tree of the hierarchy. This paper aims at solving this problem by proposing two concrete constructions of hierarchical ID-based signcryption.