AmphiKey: A Dual-Mode Secure Authenticated Key Encapsulation Protocol for Smart Grid

2025-09-01

AI Summary

To address the dual classical and quantum security threats to smart grids—requiring simultaneous confidentiality, authentication, and deniability—this paper proposes AmphiKey, a dual-mode post-quantum/legacy hybrid key encapsulation protocol. AmphiKey unifies OR-style confidentiality (i.e., security under either classical or quantum assumptions) with AND-style authentication (i.e., requiring both classical and quantum resistance). It integrates ML-KEM-768/X25519 for key exchange, ML-DSA-65/Raccoon DSA for signatures, and Ascon for hashing, enabling two operational modes: an authenticated mode (with strong identity binding) and a deniable mode (resistant to post-hoc repudiation). Leveraging mask-friendly signatures and black-box integration, AmphiKey enhances side-channel resilience. On a Raspberry Pi platform, the deniable-mode handshake completes in 0.41 ms, while server-side signature verification in authenticated mode takes 0.84 ms—demonstrating high security without compromising efficiency on resource-constrained devices.

Technology Category

• Machine Learning: Quantum Machine Learning
• Application Domains: Security
• Philosophy and Ethics of AI: Privacy & Security

Application Category

• Security and Privacy: Applications of cryptography
• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments

Abstract

AmphiKey, a dual-mode post-quantum/traditional (PQ/T) hybrid authenticated key exchange mechanism (AKEM) has been designed to secure smart grid communications against both classical and quantum threats. AmphiKey offers two distinct operational modes within a single framework: an Authenticated Mode and a Deniable Mode. The Authenticated Mode employs a blackbox approach, combining ephemeral ML-KEM-768 and X25519 with long-term Raccoon DSA keys to provide forward secrecy and strong, non-repudiable authenticity. This design achieves "OR" confidentiality, where security holds if either of the KEMs is unbroken, and robust "AND" authenticity. For the signature operation, it leverages the 'masking-friendly' Raccoon digital signature (DSA), which is specifically designed for side-channel attack resistance, though this protection is localized to the signing key and does not provide deniability. In contrast, Deniable Mode provides deniable authentication, preserving privacy. The protocol used ML-KEM-768 (AKEM-1), Ephemeral X25519 (AKEM-2), Raccoon-based DSA (Rac) (compared performance to ML-DSA-65), and the Ascon cipher to deliver its security guarantees. Key contributions include providing a flexible protocol with enhanced security, optional deniability, and efficiency adapted to the diverse needs of the smart grid infrastructure. We present a comprehensive performance evaluation on a heterogeneous testbed featuring a powerful server and client (AMD Ryzen 5) and a resource-constrained client (Raspberry Pi). In efficient Deniable mode, the full handshake completes in 0.15 ms on the server and 0.41 ms on the Raspberry Pi client. In contrast, the Authenticated Mode is bottlenecked by the client-side signature generation; the handshake takes 4.8 ms for the Raspberry Pi client to initiate and 0.84 ms for the server to verify.

Problem

• Securing smart grid communications against classical and quantum threats
• Providing both authenticated and deniable authentication modes
• Ensuring forward secrecy and side-channel attack resistance

Innovation

• Dual-mode post-quantum/traditional hybrid key exchange
• Combines ML-KEM-768 and X25519 with Raccoon DSA
• Provides authenticated and deniable operational modes