Iranian Society of Cryptology The ISC International Journal of Information Security 2008-2045 18 3 2026 07 01 QuMixnet: A Quantum-Safe Mixnet Protocol 129 141 237326 10.22042/isecure.2025.237326 EN Seyed Mohammad Dibaj Department of Electrical Engineering, Sharif University of Technology, Tehran, Iran Taraneh Eghlidos Electronics Research Institute, Sharif University of Technology, Tehran, Iran 0000-0002-3182-0277 Hosein Pilaram Electronics Research Institute, Sharif University of Technology, Tehran, Iran Journal Article The emergence of quantum computing threatens the security of traditional cryptographic primitives underpinning anonymous communication protocols like mix networks (mixnets), necessitating quantum-resistant alternatives. This paper introduces QuMixnet, a mixnet protocol designed to withstand quantum attacks while ensuring robust anonymity and privacy. QuMixnet employs post-quantum cryptographic primitives, utilizing CRYSTALS-Dilithium for digital signatures to guarantee authenticity and CRYSTALS-Kyber for key encapsulation to secure message encryption with symmetric ciphers (e.g., AES-GCM). Operating on a peer-to-peer (P2P) architecture, every node can serve as a sender, receiver, or mix node, enhancing anonymity by obscuring participant roles. Sender-determined routing ensures that only the sender knows the full message path, with onion routing layered encryption across nodes. To counter traffic analysis, QuMixnet implements message padding to a fixed size, dummy messages for traffic covering, and batch processing with shuffling. A security model, evaluated through formal security games, confirms resilience of QuMixnet against adversaries with quantum capabilities, achieving strong sender and receiver anonymity, communication anonymity, confidentiality, and integrity. QuMixnet advances anonymous communication by offering a scalable, quantum-safe solution that fortifies privacy against evolving threats.

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