Author name cluster

Paolo D'Arco

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

8 papers

2 author rows

TCS Journal 2024 Journal Article

Efficient and reliable post-quantum authentication

Paolo D'Arco
Roberto De Prisco
Angel Perez del Pozo

In this paper we propose a new lightweight authentication protocol which is efficient, reliable and, properly instantiated, suitable for the post-quantum world. It is a two-level protocol, which supports unbounded message transmission. It can be useful in several settings, from the standard sender-receiver setting, to unreliable multicast and broadcast communication in networks with resource-constrained devices. The key ideas underlying our design are mainly three: the hash-chaining method, some techniques used in MAC-based authentication protocols for multicast communication, and the use of the Guy Fawkes signatures. To our knowledge, our protocol is the first one that solves the unbounded number of message transmission issue in unreliable settings. It does not lose efficiency and introduces only a constant-size overhead in message transmission, compared to solutions assuming a bounded number of message transmissions. We rigorously model the adversarial setting and show that our protocol satisfies the definition, leveraging on standard assumptions. Apart from the technical contribution, along the line, we also point out the relevance of ideas and techniques developed in the past in the area of efficient authentication, in order to provide new authentication schemes, ready for the post-quantum world.

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TCS Journal 2023 Journal Article

Multi-stage Proof-of-Works: Properties and vulnerabilities

Paolo D'Arco
Zahra Ebadi Ansaroudi
Francesco Mogavero

Since its appearance in 2008, Bitcoin has attracted considerable attention. So far, it has been the most successful cryptocurrency, with the highest market capitalization. Nevertheless, due to the method it uses to append new transactions and blocks to the blockchain, based on a Proof-of-Work, Bitcoin suffers from poor scalability, which strongly limits the number of transactions per second and, hence, its adoption as a global payment layer for everyday uses. In this paper we analyze some recent proposals to address this issue. In particular, we focus our attention on permissionless blockchain protocols, whose distributed consensus algorithm lies on a Proof-of-Work composed of k > 1 sequential hash-puzzles, instead of a single one. Such protocols are referred to as multi-stage Proof-of-Works. We consider a simplified scenario, commonly used in the blockchain literature, in which the number of miners, their hashing powers, and the difficulty values of the hash-puzzles are constant over time. Our contribution is threefold. Firstly, we derive a closed-form expression for the mining probability of a miner, that is, the probability that the miner completes the Proof-of-Work of the next block to be added to the blockchain, before any other miner does. Secondly, we show that in multi-stage Proof-of-Works the mining probability might not be strictly related to the miner hashing power. This feature could be exploited by a smart miner, and could open up potential fairness and decentralization issues in mining. Finally, we focus on a more restricted scenario and present two attacks, which can be applied successfully against multi-stage Proof-of-Works: a Selfish Mining attack and a Selfish Stage-Withholding attack. We show that both are effective, and we point out that Selfish Stage-Withholding can be seen as a complementary strategy to Selfish Mining, which in some cases increases the selfish miner profitability in the Selfish Mining attack.

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TCS Journal 2021 Journal Article

Secret sharing schemes for infinite sets of participants: A new design technique

Paolo D'Arco
Roberto De Prisco
Alfredo De Santis

We propose a new design technique for constructing secret sharing schemes over a potentially infinite set of participants. Our findings leverage on a nice property of secret sharing schemes for finite sets of participants based on the Chinese remainder theorem: the possibility of providing shares of different sizes to participants. We successful apply the technique to the ( 3, ∞ ) -threshold access structure. The scheme we exhibit improves over the best construction currently available. Most importantly, the idea underlying the technique is of independent interest. Hopefully, it could be employed for other access structures, and in other areas of secure computation for potentially infinite sets of players.

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MFCS Conference 2018 Conference Paper

Probabilistic Secret Sharing

Paolo D'Arco
Roberto De Prisco
Alfredo De Santis
Angel L. Pérez del Pozo
Ugo Vaccaro

In classical secret sharing schemes a dealer shares a secret among a set of participants in such a way that qualified subsets can reconstruct the secret, while forbidden ones do not get any kind of information about it. The basic parameter to optimize is the size of the shares, that is, the amount of secret information that the dealer has to give to participants. In this paper we formalize a notion of probabilistic secret sharing schemes, in which qualified subsets can reconstruct the secret but only with a certain controlled probability. We show that, by allowing a bounded error in the reconstruction of the secret, it is possible to drastically reduce the size of the shares the participants get (with respect to classical secret sharing schemes). We provide efficient constructions both for threshold access structures on a finite set of participants and for evolving threshold access structures, where the set of participants is potentially infinite. Some of our constructions yield shares of constant size (i. e. , not depending on the number of participants) and an error probability of successfully reconstructing the secret which can be made as close to 1 as desired.

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TCS Journal 2016 Journal Article

Secure computation without computers

Paolo D'Arco
Roberto De Prisco

The design of secure protocols which can be used without the aid of a computer and without cryptographic knowledge is an interesting and challenging research task. Indeed, protocols enjoying these features could be useful in a variety of settings where computers cannot be used or where people feel uncomfortable to interact with or trust a computer. In this paper we make a step in such a direction: we propose a novel method for performing secure two-party computations that, apart from the setup phase, requires neither a computing machinery nor cryptographic knowledge. By merging together in a suitable way two beautiful ideas of the 80's and the 90's, Yao's garbled circuit construction and Naor and Shamir's visual cryptography, respectively, we enable Alice and Bob to securely evaluate a function f ( ⋅, ⋅ ) of their inputs, x and y, through a pure physical process. Indeed, once Alice has prepared a set of properly constructed transparencies (for this activity a computer is useful), Bob computes the function value f ( x, y ) by applying a sequence of simple steps which require the use of a pair of scissors, superposing transparencies, and the human visual system. Our construction builds on Kolesnikov's gate evaluation secret sharing schemes.

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TCS Journal 2015 Journal Article

Anonymous protocols: Notions and equivalence

Paolo D'Arco
Alfredo De Santis

Privacy protection has become a major issue in modern societies. Many efforts have been provided in the last years to catch properly the requirements that cryptographic primitives and low-level protocols should meet in order to be useful for building privacy-preserving applications. In particular, anonymity is an important property to achieve, and the notion of key privacy in public-key encryption, which guarantees that an adversary is unable to tell with which public key a certain ciphertext has been produced, plays a key-role in the design of anonymous protocols. Secret sets and anonymous broadcast encryption are two examples of useful anonymous protocols. A secret set is a representation of a subset of users of a given universe satisfying some basic membership privacy properties, and anonymous broadcast encryption is a mechanism to encrypt a broadcast message that only authorized users, whose identities are kept secret, can decrypt. In this paper we show that, even if apparently the key privacy property of an encryption scheme seems to be unrelated to the security of the encrypted content, and it looks like just an additional property the encryption scheme can enjoy, for a robust encryption scheme key privacy under chosen ciphertext attack implies non-malleability and, hence, security under chosen ciphertext attacks. This result helps to simplify the set of requirements that public key encryption schemes need to satisfy when stating and proving theorems regarding anonymous protocols in which the encryption schemes are used. Then, we provide a formal model for both secret sets and anonymous broadcast encryption and we prove that they are equivalent with respect to non-adaptive adversaries: the former can be used to design the latter and vice versa. Finally, we revisit some previous constructions for secret sets, and we analyze the security properties they enjoy within our adversarial model.

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MFCS Conference 2009 Conference Paper

Security and Tradeoffs of the Akl-Taylor Scheme and Its Variants

Paolo D'Arco
Alfredo De Santis
Anna Lisa Ferrara
Barbara Masucci

Abstract In 1983 Akl and Taylor [ Cryptographic Solution to a Problem of Access Control in a Hierarchy, ACM Transactions on Computer Systems, 1(3), 239–248, 1983] first suggested the use of cryptographic techniques to enforce access control in hierarchical structures. Over time, their scheme has been used in several different contexts, including mobile agents environments and broadcast encryption. However, it has never been fully analyzed from the security point of view. We provide a rigorous analysis of the Akl-Taylor scheme and prove that it is secure against key recovery. We also show how to obtain different tradeoffs between the amount of public information and the number of steps required to perform key derivation. Moreover, we propose a general construction to set up a key assignment scheme secure w. r. t. key indistinguishability, given any key assignment scheme secure against key recovery. Finally, we show how to use our construction, along with our tradeoffs, to obtain a variant of the Akl-Taylor scheme, secure w. r. t key indistinguishability, requiring a constant amount of public information.

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TCS Journal 2004 Journal Article

Bounds and constructions for unconditionally secure distributed key distribution schemes for general access structures

Carlo Blundo
Paolo D'Arco
Vanessa Daza
Carles Padró

In this paper we investigate the issues concerning the use of a single server across a network, the key distribution center (KDC) to enable private communications within groups of users. After providing several motivations, showing the advantages related to the distribution of the task accomplished by this server, we describe a model for such a distribution, and present bounds on the amount of resources required in a real-world implementation: random bits, memory storage, and messages to be exchanged. Moreover, we introduce a linear algebraic approach to design optimal schemes distributing a KDC, and we point out that some previous constructions belong to the proposed framework.

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