Internationalisation modes and determinants. The case of Italian automotive firms

The aim of this paper is to study the characteristics of the internationalisation process and to identify its determinants in a representative sample of firms in the Italian automotive chain. The main findings of an econometric analysis based on micro-evidence are that: a) the firms engage in complex modes of internationalisation; b) the individual firm's characteristics play a significant role; c) the firms located in the province of Turin have a clear localisation advantage, a sort of an 'industrial district' effect.Internationalisation, Firm Behaviour, Automotive Industry, Qualitative Choice Models

On the Impossibility of Algebraic NIZK In Pairing-Free Groups

Non-Interactive Zero-Knowledge proofs (NIZK) allow a prover to convince a verifier that a statement is true by sending only one message and without conveying any other information. In the CRS model, many instantiations have been proposed from group-theoretic assumptions. On the one hand, some of these constructions use the group structure in a black-box way but rely on pairings, an example being the celebrated Groth-Sahai proof system. On the other hand, a recent line of research realized NIZKs from sub-exponential DDH in pairing-free groups using Correlation Intractable Hash functions, but at the price of making non black-box usage of the group. As of today no construction is known to simultaneously reduce its security to pairing-free group problems and to use the underlying group in a black-box way. This is indeed not a coincidence: in this paper, we prove that for a large class of NIZK either a pairing-free group is used non black-box by relying on element representation, or security reduces to external hardness assumptions. More specifically our impossibility applies to two incomparable cases. The first one covers Arguments of Knowledge (AoK) which proves that a preimage under a given one way function is known. The second one covers NIZK (not necessarily AoK) for hard subset problems, which captures relations such as DDH, Decision-Linear and Matrix-DDH

A Multi-Objective Method for Short-Term Load Forecasting in European Countries

In this paper we present a novel method for daily short-term load forecasting, belonging to the class of “similar shape” algorithms. In the proposed method, a number of parameters are optimally tuned via a multi-objective strategy that minimizes the error and the variance of the error, with the objective of providing a final forecast that is at the same time accurate and reliable. We extensively compare our algorithm with other state-of-the-art methods. In particular, we apply our approach upon publicly available data and show that the same algorithm accurately forecasts the load of countries characterized by different size, different weather conditions, and generally different electrical load profiles, in an unsupervised manner

On Interactive Oracle Proofs for Boolean R1CS Statements

The framework of interactive oracle proofs (IOP) has been used with great success to construct a number of efficient transparent zk-SNARKs in recent years. However, these constructions are based on Reed-Solomon codes and can only be applied directly to statements given in the form of arithmetic circuits or R1CS over large fields $\mathbb{F}$ since their soundness error is at least $1/|\mathbb{F}|$. This motivates the question of what is the best way to apply these IOPs to statements that are naturally written as R1CS over small fields, and more concretely, the binary field $\mathbb{F}_2$. While one can just see the system as one over an extension field $\mathbb{F}_{2^e}$ containing $\mathbb{F}_2$, this seems wasteful, as it uses $e$ bits to encode just one ``information\u27\u27 bit. In fact, the recent BooLigero has devised a way to apply the well-known Ligero while being able to encode $\sqrt{e}$ bits into one element of $\mathbb{F}_{2^e}$. In this paper, we introduce a new protocol for $\mathbb{F}_2$-R1CS which among other things relies on a more efficient embedding which (for practical parameters) allows to encode $\geq e/4$ bits into an element of $\mathbb{F}_{2^e}$. Our protocol makes then black box use of lincheck and rowcheck protocols for the larger field. Using the lincheck and rowcheck introduced in Aurora and Ligero respectively we obtain $1.31 - 1.65 \times$ smaller proofs for Aurora and $3.71 \times$ for Ligero. We also estimate the reduction of prover time by a factor of $24.7 \times$ for Aurora and between $6.9 - 32.5 \times$ for Ligero without interactive repetitions. Our methodology uses the notion of reverse multiplication friendly embeddings introduced in the area of secure multiparty computation, combined with a new IOPP to test linear statements modulo a subspace $V \leq \mathbb{F}_{2^e}$ which may be of independent interest

Unbiasable Verifiable Random Functions

Verifiable Random Functions (VRFs) play a pivotal role in Proof of Stake (PoS) blockchain due to their applications in secret leader election protocols. However, the original definition by Micali, Rabin and Vadhan is by itself insufficient for such applications. The primary concern is that adversaries may craft VRF key pairs with skewed output distribution, allowing them to unfairly increase their winning chances. To address this issue David, Gaži, Kiayias and Russel (2017/573) proposed a stronger definition in the universal composability framework, while Esgin et al. (FC \u2721) put forward a weaker game-based one. Their proposed notions come with some limitations though. The former appears to be too strong, being seemingly impossible to instantiate without a programmable random oracle. The latter instead is not sufficient to prove security for VRF-based secret leader election schemes. In this work we close the above gap by proposing a new security property for VRF we call unbiasability. On the one hand, our notion suffices to imply fairness in VRF-based leader elections protocols. On the other hand, we provide an efficient compiler in the plain model (with no CRS) transforming any VRF into an unbiasable one under standard assumptions. Moreover, we show folklore VRF constructions in the ROM to achieve our notion without the need to program the random oracle. As a minor contribution, we also provide a generic and efficient construction of certified 1 to 1 VRFs from any VRF

Round-Robin is Optimal: Lower Bounds for Group Action Based Protocols

An hard homogeneous space (HHS) is a finite group acting on a set with the group action being hard to invert and the set lacking any algebraic structure. As such HHS could potentially replace finite groups where the discrete logarithm is hard for building cryptographic primitives and protocols in a post-quantum world. Threshold HHS-based primitives typically require parties to compute the group action of a secret-shared input on a public set element. On one hand this could be done through generic MPC techniques, although they incur in prohibitive costs due to the high complexity of circuits evaluating group actions known to date. On the other hand round-robin protocols only require black box usage of the HHS. However these are highly sequential procedures, taking as many rounds as parties involved. The high round complexity appears to be inherent due the lack of homomorphic properties in HHS, yet no lower bounds were known so far. In this work we formally show that round-robin protocols are optimal. In other words, any at least passively secure distributed computation of a group action making black-box use of an HHS must take a number of rounds greater or equal to the threshold parameter. We furthermore study fair protocols in which all users receive the output in the same round (unlike plain round-robin), and prove communication and computation lower bounds of $\Omega(n \log_2 n)$ for $n$ parties. Our results are proven in Shoup\u27s Generic Action Model (GAM), and hold regardless of the underlying computational assumptions

Generic Anamorphic Encryption, Revisited: New Limitations and Constructions

The notion of Anamorphic Encryption (Persiano et al. Eurocrypt 2022) aims at establishing private communication against an adversary who can access secret decryption keys and influence the chosen messages. Persiano et al. gave a simple, black-box, rejection sampling-based technique to send anamorphic bits using any IND-CPA secure scheme as underlying PKE. In this paper however we provide evidence that their solution is not as general as claimed: indeed there exists a (contrived yet secure) PKE which lead to insecure anamorphic instantiations. Actually, our result implies that such stateless black-box realizations of AE are impossible to achieve, unless weaker notions are targeted or extra assumptions are made on the PKE. Even worse, this holds true even if one resorts to powerful non-black-box techniques, such as NIZKs, $i\mathcal{O}$ or garbling. From a constructive perspective, we shed light those required assumptions. Specifically, we show that one could bypass (to some extent) our impossibility by either considering a weaker (but meaningful) notion of AE or by assuming the underlying PKE to (always) produce high min-entropy ciphertexts. Finally, we prove that, for the case of Fully-Asymmetric AE, $i\mathcal{O}$ can actually be used to overcome existing impossibility barriers. We show how to use $i\mathcal{O}$ to build Fully-Asymmetric AE (with small anamorphic message space) generically from any IND-CPA secure PKE with sufficiently high min-entropy ciphertexts. Put together our results provide a clearer picture of what black-box constructions can and cannot achieve

Verifiable Secret Sharing from Symmetric Key Cryptography with Improved Optimistic Complexity

In this paper we propose verifiable secret sharing (VSS) schemes secure for any honest majority in the synchronous model, and that only use symmetric-key cryptographic tools, therefore having plausibly post-quantum security. Compared to the state-of-the-art scheme with these features (Atapoor et al., Asiacrypt `23), our main improvement lies on the complexity of the ``optimistic\u27\u27 scenario where the dealer and all but a small number of receivers behave honestly in the sharing phase: in this case, the running time and download complexity (amount of information read) of each honest verifier is polylogarithmic and the total amount of broadcast information by the dealer is logarithmic; all these complexities were linear in the aforementioned work by Atapoor et al. At the same time, we preserve these complexities with respect to the previous work for the ``pessimistic\u27\u27 case where the dealer or $O(n)$ receivers cheat actively. The new VSS protocol is of interest in multiparty computations where each party runs one VSS as a dealer, such as distributed key generation protocols. Our main technical handle is a distributed zero-knowledge proof of low degreeness of a polynomial, in the model of Boneh et al. (Crypto `19) where the statement (in this case the evaluations of the witness polynomial) is distributed among several verifiers, each knowing one evaluation. Using folding techniques similar to FRI (Ben-Sasson et al., ICALP `18) we construct such a proof where each verifier receives polylogarithmic information and runs in polylogarithmic time

Limits of Black-Box Anamorphic Encryption

(Receiver) Anamorphic encryption, introduced by Persiano $\textit{et al.}$ at Eurocrypt 2022, considers the question of achieving private communication in a world where secret decryption keys are under the control of a dictator. The challenge here is to be able to establish a secret communication channel to exchange covert (i.e. anamorphic) messages on top of some already deployed public key encryption scheme. Over the last few years several works addressed this challenge by showing new constructions, refined notions and extensions. Most of these constructions, however, are either ad hoc, in the sense that they build upon specific properties of the underlying PKE, or impose severe restrictions on the size of the underlying anamorphic message space. In this paper we consider the question of whether it is possible to have realizations of the primitive that are both generic and allow for large anamorphic message spaces. We give strong indications that, unfortunately, this is not the case. Our first result shows that $\textit{any black-box realization}$ of the primitive, i.e. any realization that accesses the underlying PKE only via oracle calls, $\textit{must}$ have an anamorphic message space of size at most $poly(\lambda)$ ($\lambda$ security parameter). Even worse, if one aims at stronger variants of the primitive (and, specifically, the notion of asymmetric anamorphic encryption, recently proposed by Catalano $\textit{et al.}$) we show that such black-box realizations are plainly impossible, i.e. no matter how small the anamorphic message space is. Finally, we show that our impossibility results are rather tight: indeed, by making more specific assumptions on the underlying PKE, it becomes possible to build generic AE where the anamorphic message space is of size $\Omega(2^\lambda)$

Anamorphic Encryption: New Constructions and Homomorphic Realizations

The elegant paradigm of Anamorphic Encryption (Persiano et al., Eurocrypt 2022) considers the question of establishing a private communication in a world controlled by a dictator. The challenge is to allow two users, sharing some secret anamorphic key, to exchange covert messages without the dictator noticing, even when the latter has full access to the regular secret keys. Over the last year several works considered this question and proposed constructions, novel extensions and strengthened definitions. In this work we make progress on the study of this primitive in three main directions. First, we show that two general and well established encryption paradigms, namely hybrid encryption and the IBE-to-CCA transform, admit very simple and natural anamorphic extensions. Next, we show that anamorphism, far from being a phenomenon isolated to basic encryption schemes, extends also to homomorphic encryption. We show that some existing homomorphic schemes, (and most notably the fully homomorphic one by Gentry, Sahai and Waters) can be made anamorphic, while retaining their homomorphic properties both with respect to the regular and the covert message. Finally we refine the notion of anamorphic encryption by envisioning the possibility of splitting the anamorphic key into an encryption component (that only allows to encrypt covert messages) and a decryption component. This makes possible for a receiver to set up several, independent, covert channels associated with a single covert key