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Faster Kyber and Saber via a Generic Fujisaki-Okamoto Transform for Multi-User Security in the QROM

June 9, 2021


Julien Duman - Ruhr-Universität Bochum


Constructing an efficient CCA-secure KEM is generally done by first constructing a passively-secure PKE scheme, and then applying the Fujisaki-Okamoto (FO) transformation. The original FO transformation was designed to offer security in a single user setting. A stronger notion, known as multi-user security, considers the attacker’s advantage in breaking one of many user’s ciphertexts. Bellare et al. (EUROCRYPT 2020) showed that standard single user security implies multi-user security with a multiplicative tightness gap equivalent to the number of users.

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Related Topics

Security and Privacy: post-quantum cryptography

Created June 09, 2021, Updated June 10, 2021