FORT: A Forward Secure and Threshold Authorized Multi-Authority Attribute-Based Signature Scheme for Multimedia IoT

Attribute-Based Signature (ABS) provides a critical solution for ensuring data integrity, fine-grained access control, and anonymous authentication in security-sensitive systems such as the Multimedia Internet of Things (MIoT) and multimedia streaming platforms. However, practical adoption of ABS faces three fundamental challenges: vulnerability to key exposure and escrow risks, linear growth of computational cost, and insufficient robustness in multi-authority environments. To address these issues, we propose a forward secure and threshold authorized multi-authority ABS scheme called FORT in this paper. By employing a binary tree structure to divide multiple time periods, historical signatures remain valid even in the event of key exposure. Furthermore, to balance robustness and resistance to corruption while mitigating the key escrow problem, we construct a threshold authorized multi-authority structure based on Lagrange interpolation. This structure effectively reduces the impact of a single authority on the MIoT. Additionally, through the adoption of outsourced computation technology, which offloads complex computations in the signature and verification phases to the edge server, the computational burden for both the signer and verifier is significantly reduced to a small constant. Rigorous security analysis demonstrates that the FORT scheme achieves forward security, collusion attack resistance, corrupt authority resistance and anonymity. Theoretical comparisons and simulation experiments demonstrate the lightweight nature of the FORT scheme in terms of computation and communication.