International Association
for Cryptologic Research

Polynomial multiplication over $\mathbb{F}_2[x]$ is a fundamental building block in code-based and lattice-based cryptography, particularly on lightweight embedded devices where dedicated carry-less multiply instructions are unavailable. This paper presents a high-speed, constant-time implementation of radix-16 polynomial multiplication on the ARM Cortex-M4, combining zero-padding with recursive Karatsuba layers. Building on the radix-16 decomposition proposed by Chen et al. in TCHES’21, we replace the conventional schoolbook inner multiplier with a multi-level Karatsuba scheme. This optimization reduces cycle counts on the ARM Cortex-M4 while preserving constant-time execution. To further optimize efficiency, the design minimizes packing and unpacking overhead by operating at 128-bit granularity and employs a five-stage pipeline—Decomposition, Padding, Multiplication, Unpadding, and Reassembly—implemented entirely with data-independent shifts, XORs, and masks. Experimental results on the Cortex-M4 show that our optimized $ct\_poly32\_mul\_64\_bit$ implementation achieves up to 31\% improvement over the best existing constant-time baseline, demonstrating the efficiency and scalability of recursive Karatsuba for resource-constrained cryptographic applications.

We propose CA-MCPQ, a context-aware post-quantum-secure extension of the Model Context Protocol (MCP). Unlike standard MCP, which leaves authentication, encryption, and authorization optional or implementation-specific, CA-MCPQ elevates them to mandatory protocol-level mechanisms. The design incorporates post-quantum mutual authentication, KEM-derived session keys, and authenticated sequencing to ensure session integrity and prevent replay. Role-based access control is enforced, while token-based authentication is eliminated entirely. AI dynamically infers the required security tier from contextual information and negotiates compatible PQC algorithms; each response returns a reliability score that quantifies alignment with the requested security level.

This architecture addresses critical vulnerabilities of MCP—including token misuse, session hijacking, impersonation, and quantum attack—while preserving interoperability. Notably, our evaluation shows that the cryptographic and transport overheads are negligible compared to model computation, confirming that strong post-quantum assurances can be achieved without degrading system performance. Overall, CA-MCPQ provides a practical path toward secure-by-design AI agent ecosystems and lays the groundwork for future extensions such as agent–agent secure coordination.

We present Olingo, a framework for threshold lattice signatures that is the first to offer all desired properties for real-world implementations of quantum-secure threshold signatures: small keys and signatures, low communication and round complexity, non-interactive online signing, distributed key generation (DKG), and identifiable abort.

Our starting point is the framework of Gur, Katz, and Silde (PQCrypto 2024). We change the underlying signature scheme to Raccoon (Katsumata et al., Crypto 2024), remove the trapdoor commitments, and apply numerous improvements and optimizations to achieve all the above properties. We provide detailed proofs of security for our new framework and present concrete parameters and benchmarks.

At the $128$-bit security level, for up to $1024$ parties and supporting $2^{60}$ signatures, our scheme has $2.6$ KB public keys and $9.7$ KB signatures; while signing requires communication of $953$ KB per party. Using the LaBRADOR proof system (Beullens and Seiler, Crypto 2023), this can be further reduced to $596$ KB. An optimistic non-interactive version of our scheme requires only $83$ KB communication per party.