Threshold Attribute-based Signcryption with Constant-Size Ciphertexts and Public Verifiability

Threshold attribute based signcryption provides the flexible access control policy, and achieves sender anonymity, confidentiality, unforgeability and collusion resilience. While, the existed schemes are inefficient for cipher text lengths are linear functions of the attributes number. The paper employ Inner-product encryption, presented the first scheme of threshold attribute based signcryption with constant-size ciphertexts. Secure analysis in the standard model shows that, the proposal achieves unforgeability against chosen-message attack and indistinguishability against chosen-plaintext attack, under chosen-attribute set. The constant-size ciphertexts of the proposal is 5 vertical bar G(1) vertical bar + vertical bar G(2) vertical bar, and has no relation with the attribute number. It reduces the communication overheads significantly. Additionally, the proposed scheme also could be verified publicly, which improves the security further more.