Fiore, DarioGonzález Vasco, María IsabelSoriente, Claudio2023-12-132023-12-132017-12Fiore, D., González Vasco, M. I., & Soriente, C. (2017). Partitioned Group Password-Based Authenticated Key Exchange. The Computer Journal, 60(12), 1912-1922.0010-4620https://hdl.handle.net/10016/39076Group Password-Based Authenticated Key Exchange (GPAKE) allows a group of users to establish a secret key, as long as all of them share the same password. However, in existing GPAKE protocols as soon as one user runs the protocol with a non-matching password, all the others abort and no key is established. In this paper we seek for a more flexible, yet secure, GPAKE and put forward the notion of partitioned GPAKE. Partitioned GPAKE tolerates users that run the protocol on different passwords. Through a protocol run, any subgroup of users that indeed share a password, establish a session key, factoring out the 'noise' of inputs by users holding different passwords. At the same time any two keys, each established by a different subgroup of users, are pair-wise independent if the corresponding subgroups hold different passwords. We also introduce the notion of password-privacy for partitioned GPAKE, which is a kind of affiliation hiding property, ensuring that an adversary should not be able to tell whether any given set of users share a password. Finally, we propose an efficient instantiation of partitioned GPAKE building on an unforgeable symmetric encryption scheme and a PAKE by Bellare et al. Our proposal is proven secure in the random oracle/ideal cipher model, and requires only two communication rounds.11eng© 2023 Oxford University Press.Group Key ExchangePassword AuthenticationSecurity Modelsresearch articleInformáticaMatemáticasTelecomunicacioneshttps://doi.org/10.1093/comjnl/bxx078open access1912121922The Computer Journal60AR/0000032343