Generalised entropy accumulation for quantum cryptography

ZOOM - IQC Math and CS Seminar Featuring Tony Metger, ETH Zurich

To use a cryptographic protocol in practice, one has to prove that it is secure against general attacks: even if an adversary performs a complicated attack involving all of the rounds of the protocol, they cannot compromise security. A much simpler task is to prove security against collective attacks, where the adversary is assumed to behave the same in each round. In this work, we develop a new information-theoretic tool, called the generalised entropy accumulation theorem (GEAT), for reducing security against general attacks to security against collective attacks. The GEAT is a generalisation of the entropy accumulation theorem [DFR20], but considers a significantly more general model of quantum side information. As a result, it is much more broadly and easily applicable. For example, it is the first general proof technique that can handle mistrustful device-independent cryptography, allowing us to give the first security proof of blind randomness expansion against general attacks. Furthermore, the GEAT is a useful tool for proving the security of QKD protocols as it can be applied directly to prepare-and-measure protocols without transforming them into an entanglement-based version.

[arXiv:2203.04989 and arXiv:2203.04993]

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