Fast Scloud+: A High-Speed Hardware Implementation for Unstructured-LWE-Based Post-Quantum Cryptography

Abstract. This paper presents Fast Scloud+, a high-speed hardware implementation of Scloud+, an unstructured-LWE-based key encapsulation mechanism (KEM). Unlike lattice-based KEMs relying on ring or module structures, Scloud+ is built on plain LWE, offering stronger security guarantees against structural attacks. We design optimized hardware architectures to accelerate the core operations of Scloud+, including matrix-vector multiplications, error reconciliation, and lattice encoding/decoding. Our FPGA implementation achieves significant throughput improvements over software implementations while maintaining moderate resource utilization. When targeting 128, 192, and 256-bit security levels, Fast Scloud+ demonstrates competitive hardware efficiency compared to other post-quantum KEM implementations, making it suitable for deployment in performance-constrained environments.