## CryptoDB

### Dario Catalano

#### Publications

Year
Venue
Title
2020
PKC
Threshold Signatures allow n parties to share the power of issuing digital signatures so that any coalition of size at least $t+1$ can sign, whereas groups of t or less players cannot. Over the last few years many schemes addressed the question of realizing efficient threshold variants for the specific case of EC-DSA signatures. In this paper we present new solutions to the problem that aim at reducing the overall bandwidth consumption. Our main contribution is a new variant of the Gennaro and Goldfeder protocol from ACM CCS 2018 that avoids all the required range proofs, while retaining provable security against malicious adversaries in the dishonest majority setting. Our experiments show that – for all levels of security – our signing protocol reduces the bandwidth consumption of best previously known secure protocols for factors varying between 4.4 and 9, while key generation is consistently two times less expensive. Furthermore compared to these same protocols, our signature generation is faster for 192-bits of security and beyond.
2020
PKC
In this paper we present a new 2-party protocol for secure computation over rings of the form $mathbb {Z}_{2^k}$ . As many recent efficient MPC protocols supporting dishonest majority, our protocol consists of a heavier (input-independent) pre-processing phase and a very efficient online stage. Our offline phase is similar to BeDOZa (Bendlin et al. Eurocrypt 2011) but employs Joye-Libert (JL, Eurocrypt 2013) as underlying homomorphic cryptosystem and, notably, it can be proven secure without resorting to the expensive sacrifice step. JL turns out to be particularly well suited for the ring setting as it naturally supports $mathbb {Z}_{2^k}$ as underlying message space. Moreover, it enjoys several additional properties (such as valid ciphertext-verifiability and efficiency) that make it a very good fit for MPC in general. As a main technical contribution we show how to take advantage of all these properties (and of more properties that we introduce in this work, such as a ZK proof of correct multiplication) in order to design a two-party protocol that is efficient, fast and easy to implement in practice. Our solution is particularly well suited for relatively large choices of k ( e.g. $k=128$ ), but compares favorably with the state of the art solution of SPD $mathbb {Z}_{2^k}$ (Cramer et al. Crypto 2018) already for the practically very relevant case of $mathbb {Z}_{2^{64}}$ .
2020
ASIACRYPT
We construct new functional encryption schemes that combine the access control functionality of attribute-based encryption with the possibility of performing linear operations on the encrypted data. While such a primitive could be easily realized from fully fledged functional encryption schemes, what makes our result interesting is the fact that our schemes simultaneously achieve all the following properties. They are public-key, efficient and can be proved secure under standard and well established assumptions (such as LWE or pairings). Furthermore, security is guaranteed in the setting where adversaries are allowed to get functional keys that decrypt the challenge ciphertext. Our first results are two functional encryption schemes for the family of functions that allow users to embed policies (expressed by monotone span programs) in the encrypted data, so that one can generate functional keys to compute weighted sums on the latter. Both schemes are pairing-based and quite generic: they combine the ALS functional encryption scheme for inner products from Crypto 2016 with any attribute-based encryption schemes relying on the dual-system encryption methodology. As an additional bonus, they yield simple and elegant multi-input extensions essentially for free, thereby broadening the set of applications for such schemes. Multi-input is a particularly desirable feature in our setting, since it gives a finer access control over the encrypted data, by allowing users to associate different access policies to different parts of the encrypted data. Our second result builds identity-based functional encryption for inner products from lattices. This is achieved by carefully combining existing IBE schemes from lattices with adapted, LWE-based, variants of ALS. We point out to intrinsic technical bottlenecks to obtain richer forms of access control from lattices. From a conceptual point of view, all our results can be seen as further evidence that more expressive forms of functional encryption can be realized under standard assumptions and with little computational overhead.
2019
CRYPTO
ECDSA is a widely adopted digital signature standard. Unfortunately, efficient distributed variants of this primitive are notoriously hard to achieve and known solutions often require expensive zero knowledge proofs to deal with malicious adversaries. For the two party case, Lindell [Lin17] recently managed to get an efficient solution which, to achieve simulation-based security, relies on an interactive, non standard, assumption on Paillier’s cryptosystem. In this paper we generalize Lindell’s solution using hash proof systems. The main advantage of our generic method is that it results in a simulation-based security proof without resorting to non-standard interactive assumptions.Moving to concrete constructions, we show how to instantiate our framework using class groups of imaginary quadratic fields. Our implementations show that the practical impact of dropping such interactive assumptions is minimal. Indeed, while for 128-bit security our scheme is marginally slower than Lindell’s, for 256-bit security it turns out to be better both in key generation and signing time. Moreover, in terms of communication cost, our implementation significantly reduces both the number of rounds and the transmitted bits without exception.
2018
JOFC
2018
CRYPTO
We present new constructions of multi-input functional encryption (MIFE) schemes for the inner-product functionality that improve the state of the art solution of Abdalla et al. (Eurocrypt 2017) in two main directions.First, we put forward a novel methodology to convert single-input functional encryption for inner products into multi-input schemes for the same functionality. Our transformation is surprisingly simple, general and efficient. In particular, it does not require pairings and it can be instantiated with all known single-input schemes. This leads to two main advances. First, we enlarge the set of assumptions this primitive can be based on, notably, obtaining new MIFEs for inner products from plain DDH, LWE, and Decisional Composite Residuosity. Second, we obtain the first MIFE schemes from standard assumptions where decryption works efficiently even for messages of super-polynomial size.Our second main contribution is the first function-hiding MIFE scheme for inner products based on standard assumptions. To this end, we show how to extend the original, pairing-based, MIFE by Abdalla et al. in order to make it function hiding, thus obtaining a function-hiding MIFE from the MDDH assumption.
2017
CRYPTO
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
CRYPTO
2014
CRYPTO
2014
PKC
2014
EPRINT
2014
JOFC
2014
ASIACRYPT
2013
PKC
2013
TCC
2013
EUROCRYPT
2012
PKC
2011
JOFC
2011
EUROCRYPT
2011
PKC
2009
EUROCRYPT
2008
PKC
2008
EUROCRYPT
2008
JOFC
2007
PKC
2007
JOFC
2006
TCC
2006
EPRINT
In this paper we introduce a new primitive called identity-based encryption with wildcards, or WIBE for short. It allows to encrypt messages to a whole range of users simultaneously whose identities match a certain pattern. This pattern is defined through a sequence of fixed strings and wildcards, where any string can take the place of a wildcard in a matching identity. Our primitive can be applied to provide an intuitive way to send encrypted email to groups of users in a corporate hierarchy. We propose a full security notion and give efficient implementations meeting this notion under different pairing-related assumptions, both in the random oracle model and in the standard model.
2005
CRYPTO
2005
PKC
2005
EPRINT
We identify and fill some gaps with regard to consistency (the extent to which false positives are produced) for public-key encryption with keyword search (PEKS). We define computational and statistical relaxations of the existing notion of perfect consistency, show that the scheme of Boneh et al. in Eurocrypt 2004 is computationally consistent, and provide a new scheme that is statistically consistent. We also provide a transform of an anonymous IBE scheme to a secure PEKS scheme that, unlike the previous one, guarantees consistency. Finally, we suggest three extensions of the basic notions considered here, namely anonymous HIBE, public-key encryption with temporary keyword search, and identity-based encryption with keyword search.
2004
CRYPTO
2004
PKC
2003
ASIACRYPT
2002
ASIACRYPT
2002
EPRINT
We introduce a model for electronic election schemes that involves a more powerful adversary than in previous work. In particular, we allow the adversary to demand of coerced voters that they vote in a particular manner, abstain from voting, or even disclose their secret keys. We define a scheme to be _coercion-resistant_ if it is infeasible for the adversary to determine whether a coerced voter complies with the demands. A first contribution of this paper is to describe and characterize a new and strengthened adversary for coercion in elections. (In doing so, we additionally present what we believe to be the first formal security definitions for electronic elections of _any_ type.) A second contribution is to demonstrate a protocol that is secure against this adversary. While it is clear that a strengthening of attack models is of theoretical relevance, it is important to note that our results lie close to practicality. This is true both in that we model real-life threats (such as vote-buying and vote-cancelling), and in that our proposed protocol combines a fair degree of efficiency with an unusual lack of structural complexity. Furthermore, while previous schemes have required use of an untappable channel, ours only carries the much more practical requirement of an anonymous channel.
2002
JOFC
2001
EUROCRYPT
2000
EUROCRYPT
1998
CRYPTO

Crypto 2019
PKC 2019
PKC 2018
Eurocrypt 2016
Crypto 2016
PKC 2016
Crypto 2015
Eurocrypt 2014
PKC 2012
Eurocrypt 2012
PKC 2010
TCC 2010
Eurocrypt 2007