@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 {10.1007/978-3-030-57990-6_33,
	title = {On Adaptive Security of Delayed-Input Sigma Protocols and Fiat-Shamir NIZKs},
	journal = {Security and Cryptography for Networks},
	year = {2020},
	pages = {670{\textendash}690},
	publisher = {Springer International Publishing},
	address = {Cham},
	abstract = {We study adaptive security of delayed-input Sigma protocols and non-interactive zero-knowledge (NIZK) proof systems in the common reference string (CRS) model. Our contributions are threefold:We exhibit a generic compiler taking any delayed-input Sigma protocol and returning a delayed-input Sigma protocol satisfying adaptive-input special honest-verifier zero knowledge (SHVZK). In case the initial Sigma protocol also satisfies adaptive-input special soundness, our compiler preserves this property.We revisit the recent paradigm by Canetti et al. (STOC 2019) for obtaining NIZK proof systems in the CRS model via the Fiat-Shamir transform applied to so-called trapdoor Sigma protocols, in the context of adaptive security. In particular, assuming correlation-intractable hash functions for all sparse relations, we prove that Fiat-Shamir NIZKs satisfy either: (i)Adaptive soundness (and non-adaptive zero knowledge), so long as the challenge is obtained by hashing both the prover{\textquoteright}s first round and the instance being proven;(ii)Adaptive zero knowledge (and non-adaptive soundness), so long as the challenge is obtained by hashing only the prover{\textquoteright}s first round, and further assuming that the initial trapdoor Sigma protocol satisfies adaptive-input SHVZK.We exhibit a generic compiler taking any Sigma protocol and returning a trapdoor Sigma protocol. Unfortunately, this transform does not preserve the delayed-input property of the initial Sigma protocol (if any). To complement this result, we also give yet another compiler taking any delayed-input trapdoor Sigma protocol and returning a delayed-input trapdoor Sigma protocol with adaptive-input SHVZK.},
	isbn = {978-3-030-57990-6},
	author = {Ciampi, Michele and Parisella, Roberto and Venturi, Daniele},
	editor = {Galdi, Clemente and Kolesnikov, Vladimir}
}
