The ISC International Journal of Information Security

Abstract 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.