@inproceedings {43112,
	title = {Multi-Instance Secure Public-Key Encryption},
	journal = {PKC 2023, Part II},
	year = {2023},
	month = {05/2023},
	pages = {336-367},
	publisher = {Springer Nature Switzerland},
	address = {Cham},
	abstract = {Mass surveillance targets many users at the same time with the goal of learning as much as possible. Intuitively, breaking many users{\textquoteright} cryptography simultaneously should be at least as hard as that of only breaking a single one, but ideally security degradation is gradual: an adversary ought to work harder to break more. Bellare, Ristenpart and Tessaro (Crypto{\textquoteright}12) introduced the notion of multi-instance security to capture the related concept for password hashing with salts. Auerbach, Giacon and Kiltz (Eurocrypt{\textquoteright}20) motivated the study of public key encryption (PKE) in the multi-instance setting, yet their technical results are exclusively stated in terms of key encapsulation mechanisms (KEMs), leaving a considerable gap. We investigate the multi-instance security of public key encryption. Our contributions are twofold. Firstly, we define and compare possible security notions for multi-instance PKE, where we include PKE schemes whose correctness is not perfect. Secondly, we observe that, in general, a hybrid encryption scheme of a multi-instance secure KEM and an arbitrary data encapsulation mechanism (DEM) is unlikely to inherit the KEM{\textquoteright}s multi-instance security. Yet, we show how with a suitable information-theoretic DEM, and a computationally secure key derivation function if need be, inheritance is possible. As far as we are aware, ours is the first inheritance result in the challenging multi-bit scenario.},
	keywords = {Hybrid Encryption, Mass Surveillance, Multi-Instance Security, Property Inheritance},
	isbn = {978-3-031-31370-7},
	doi = {10.1007/978-3-031-31371-4_12},
	url = {https://doi.org/10.1007/978-3-031-31371-4_12},
	author = {Brunetta, Carlo and Heum, Hans and Stam, Martijn},
	editor = {Boldyreva, Alexandra and Kolesnikov, Vladimir}
}
@inproceedings {28385,
	title = {Stupid, Evil, or Both? Understanding the Smittestopp conflict},
	journal = {The 14th Norwegian Information Security Conference (NISK 2021)},
	volume = {14},
	year = {2021},
	month = {12/2021},
	pages = {88-96},
	publisher = {NTNU},
	abstract = {Like many governments, the Norwegian government provided a contact tracing application to help in combating the COVID-19 pandemic at its outset. However, the application was widely criticized for enabling an unacceptable intrusion into its subjects{\textquoteright} lives, leading to its discontinuation only four months into the pandemic. In this essay, we will take a closer look at what went wrong, attempt to gain a deeper understanding of the passionate nature of the conflict, and how both sides came to view the other as being either stupid, or evil, or both.},
	keywords = {Code of Ethics, Contact Tracing, Privacy, Smittestopp},
	url = {https://www.ntnu.edu/nikt2021},
	author = {Heum, Hans},
	editor = {Costache, Anamaria and Stig F. {Mj{\o}lsnes}}
}
@inproceedings {28379,
	title = {Tightness Subtleties for Multi-user PKE Notions},
	journal = {18th IMA International Conference on Cryptography and Coding},
	volume = {13129},
	year = {2021},
	month = {12/2021},
	pages = {75 - 104},
	publisher = {Springer International Publishing},
	edition = {18},
	address = {Cham},
	abstract = {Public key encryption schemes are increasingly being studied concretely, with an emphasis on tight bounds even in a multi-user setting. Here, two types of formalization have emerged, one with a single challenge bit and one with multiple challenge bits. Another modelling choice is whether to allow key corruptions or not. How tightly the various notions relate to each other has hitherto not been studied in detail. We show that in the absence of corruptions, single-bit left-or-right indistinguishability is the preferred notion, as it tightly implies the other (corruption-less) notions. However, in the presence of corruptions, this implication no longer holds; we suggest the use of a more general notion that tightly implies both existing options. Furthermore, for completeness we study how the relationship between left-or-right versus real-or-random evolves in the multi-user PKE setting.},
	isbn = {978-3-030-92640-3},
	issn = {0302-9743},
	doi = {10.1007/978-3-030-92641-010.1007/978-3-030-92641-0_5},
	url = {https://link.springer.com/content/pdf/10.1007/978-3-030-92641-0_5},
	author = {Heum, Hans and Stam, Martijn},
	editor = {Paterson, Maura}
}
