Informatica

Anonymous multi-recipient signcryption (AMRS) is an important scheme of public-key cryptography (PKC) and applied for many modern digital applications. In an AMRS scheme, a broadcast management centre (BMC) may sign and encrypt a plaintext data (or file) to a set of multiple recipients. Meanwhile, only these recipients in the set can decrypt the plaintext data and authenticate the BMC while offering anonymity of their identities. In the past, some AMRS schemes based on various PKCs have been proposed. Recently, due to side-channel attacks, the existing cryptographic mechanisms could be broken so that leakage-resilient PKC resisting such attacks has attracted the attention of cryptographic researches. However, the work on the design of leakage-resilient AMRS (LR-AMRS) schemes is little and only suitable for multiple recipients under a single PKC. In this paper, the first leakage-resilient and seamlessly compatible AMRS (LRSC-AMRS) in heterogeneous PKCs is proposed. In the proposed scheme, multiple recipients can be members of two heterogeneous PKCs, namely, the public-key infrastructure PKC (PKI-PKC) or the certificateless PKC (CL-PKC). Also, we present a seamlessly compatible upgradation procedure from the PKI-PKC to the CL-PKC. The proposed scheme achieves three security properties under side-channel attacks, namely, encryption confidentiality, recipient anonymity and sender (i.e. BMC) authentication, which are formally shown by the associated security theorems. Finally, by comparing with related schemes, it is shown that the proposed LRSC-AMRS scheme is suitable for heterogeneous recipients and the computational cost of each recipient’s unsigncryption algorithm is constant $O(1)$.

User anonymity is very important security technique in distributed computing environments that an illegal entity cannot determine any information concerning the user's identity. In 2006, Kumar–Rajendra proposed a Secure Identification and Key agreement protocol with user Anonymity (SIKA). This paper demonstrates the vulnerability of the SIKA protocol and then presents an improvement to repair the security flaws of the SIKA protocol.