Keymix: Protecting Large Resources From Key Exfiltration

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When transmitted over public networks, high-value resources must be protected against unauthorized access. Although traditional encryption schemes provide confidentiality in transit, they offer no guarantees if the encryption key is exfiltrated through side-channel attacks or other means. Leakage-resilient schemes aim to remain secure under partial key leakage; however, existing constructions require strong assumptions on leakage timing or restrict the adversary to inaccessible memory regions, rendering them impractical for real deployments. In this paper, we introduce Keymix, a novel encryption scheme designed to protect large resources in the presence of key exfiltration. Keymix supports encryption with a configurable big-key K (up to GiBs in size), ensuring that a plaintext R (with |R| ≥ |K|) cannot be fully recovered unless the K is fully exfiltrated, even when the adversary possesses the complete ciphertext. Unlike prior work, security depends solely on the exfiltrated portion of K, without assumptions on leakage timing or inaccessible memory regions.

We implement Keymix using AES and achieve a throughput of 1.6 GiB/s on commodity hardware. Moreover, we demonstrate its practicality through integration with modern cloud infrastructure inside a Kubernetes cluster, where it transparently applies exfiltration-resistant encryption to storage blocks during service restore and backup.

@inproceedings{keymix,
	author = {Marco Abbadini and Michele Beretta and Sabrina {De Capitani di
	          Vimercati} and Dario Facchinetti and Sara Foresti and Stefano
	          Paraboschi and Matthew Rossi and Pierangela Samarati},
	booktitle = {Proceedings of the International Conference on Network and
	             System Security (NSS)},
	title = {Keymix: Protecting Large Resources From Key Exfiltration},
	month = {October},
	year = {2026},
	location = {Hangzhou, China},
}