The COVID19 pandemic is having a worldwide impact on the way business is conducted, people interact, work is organised, and more. In a line, it is changing our way of life. In this Special Issue: COVID-19 and Cybersecurity, we focus on the many ramifications of COVID-19 into the Cybersecurity realm. Other Information Published in: IET Information Security License: http://creativecommons.org/licenses/by-nc/4.0/ See article on publisher's website: https://dx.doi.org/10.1049/ise2.12084

A major issue for many applications of blockchain technology is the tension between immutability and compliance to regulations. For instance, the GDPR in the EU requires to guarantee, under some circumstances, the right to be forgotten. This could imply that at some point one might be forced to delete some data from a locally stored blockchain, therefore irreparably hurting the security and transparency of such decentralized platforms. Motivated by such data protection and consistency issues, in this work we design and implement a mechanism for securely deleting data from Bitcoin blockchain. We use zero-knowledge proofs to allow any node to delete some data from Bitcoin transactions, still preserving the public verifiability of the correctness of the spent and spendable coins. Moreover, we specifically use STARK proofs to exploit the transparency that they provide. Our solution, unlike previous approaches, avoids the complications of asking nodes to reach consensus on the content to delete. In particular, our design allows every node to delete some specific data without coordinating this decision with others. In our implementation, data removal can be performed (resp., verified) in minutes (resp., seconds) on a standard laptop rather than in days as required in previous designs based on consensus.

In e-voting protocols, cryptographers must balance usability with strong security guarantees, such as privacy and verifiability. In traditional e-voting protocols, privacy is often provided by a trusted authority that learns the votes and computes the tally. Some protocols replace the trusted authority by a set of authorities, and privacy is guaranteed if less than a threshold number of authorities are corrupt. For verifiability, stronger security is demanded. Typically, corrupt authorities that try to fake the tally result must always be detected.To provide verifiability, many e-voting protocols use Non-Interactive Zero-Knowledge proofs (NIZK). Thanks to their non-interactive nature, NIZK allow anybody, including third parties that do not participate in the protocol, to verify the correctness of the tally. Therefore, NIZK can be used to obtain universal verifiability. Additionally, NIZK also improve usability because they allow voters to cast a vote non-interactively.The disadvantage of NIZK is that their security is based on setup assumptions such as the common reference string (CRS) or the random oracle model. The former requires a trusted party to generate a CRS. The latter, though a popular model for secure protocol design, has been shown to be unsound.We address the design of e-voting protocols that provide verifiability without any trust assumptions. We show that Non-Interactive Witness-Indistinguishable proofs can be used for this purpose. Our e-voting protocols are private under the Decision Linear assumption, while perfect individual verifiability, i.e. a fake tally is detected with probability 1, holds unconditionally. Perfect universal verifiability requires a trusted public bulletin board. We remark that our definition of verifiability does not consider eligibility or end-to-end verifiability. First, we present a general construction that supports any tally function. Then, we show how to efficiently instantiate it for specific types of elections through Groth-Sahai proofs.

Deniable encryption, first introduced by Canetti et al . 1997, allows equivocation of encrypted communication. In this work, the authors generalise its study to functional encryption (FE). The authors’ results are summarised as follows: They first put forward and motivate the concept of receiver‐deniable FE, for which they consider two models. In the first model, as previously considered by O'Neill et al . 2011 in the case of identity‐based encryption, a receiver gets assistance from the master authority to generate a fake secret key. In the second model, there are ‘normal’ and ‘deniable’ secret keys, and a receiver in possession of a deniable secret key can produce a fake but authentic‐looking normal key on its own. In the first model, they show a compiler from any FE scheme for circuits to a FE scheme having receiver deniability. In addition, they show an efficient receiver‐deniable FE scheme for Boolean formulae from bilinear maps. In the second (multi‐distributional) model, they present a specific FE scheme for circuits having receiver deniability. To the authors’ knowledge, a scheme in the multi‐distributional model was not previously known even for the special case of identity‐based encryption. Finally, they construct the first sender (non‐multi‐distributional) deniable FE scheme.

In the public‐key setting, known constructions of function‐private functional encryption (FPFE) were limited to very restricted classes of functionalities like inner‐product. Moreover, its power has not been well investigated. The authors construct FPFE for general functions and explore its powerful applications, both for general and specific functionalities. One key observation entailed by their results is that attribute‐based encryption with function privacy implies FE, a notable fact that sheds light on the importance of the function privacy property for FE.

Security models for PAKE protocols aim to capture the desired security properties that such protocols must satisfy when executed in the presence of an active adversary. They are usually classified into i) indistinguishability-based (IND-based) or ii) simulation-based (SIM-based). The relation between these two security notions is unclear and mentioned as a gap in the literature. In this work, we prove that the SIM-based model of Boyko, Mackenzie and Patel [EUROCRYPT00] and the IND-based model of Abdalla, Fouque and Pointcheval are equivalent, in the sense that a protocol proven secure in one model is also secure in the other model.

We introduce the notion of privacy-preserving verifiability for security protocols. It holds when a protocol admits a verifiability test that does not reveal, to the verifier that runs it, more pieces of information about the protocol’s execution than those required to run the test. Our definition of privacy-preserving verifiability is general and applies to cryptographic protocols as well as to human security protocols. In this paper we exemplify it in the domain of e-exams. We prove that the notion is meaningful by studying an existing exam protocol that is verifiable but whose verifiability tests are not privacy-preserving. We prove that the notion is applicable: we review the protocol using functional encryption so that it admits a verifiability test that preserves privacy according to our definition. We analyse, in ProVerif, that the verifiability holds despite malicious parties and that the new protocol maintains all the security properties of the original protocol, so proving that our privacy-preserving verifiability can be achieved starting from existing security

It has been recently discovered that some cyclic groups that could be used in Cryptography admit a special bilinear pairing map that introduces extra structure to the group. Bilinear pairing maps were first used to break cryptosystems (see, for example, ) and later it was realized that the extra structure could be exploited to build cryptosystems with extra properties. Boneh and Franklins identity-based encryption scheme is the most famous early example of what could be achieved using bilinear maps. After that, a plethora of cryptosystems have been designed using bilinear maps. No full and freely available implementation of pairing based cryptography was available until this work. Recent proposals fall short of this goal as either their source code is not available or because they support a limited range of elliptic curve. Moreover, neither one of implements preprocessing that is crucial to reduce the computation time. In this work, we present jPBC a Java port of the PBC library written in C. jPBC provides a full ecosystem of interfaces and classes to simplify the use of the bilinear maps even for a non-cryptographer. jPBC supports different types of elliptic curves, preprocessing which can speedup the computation significantly and it is ready for the mobile world. Moreover a benchmark comparison between jPBC and PBC has been performed to measure the gap between the two libraries. Furthermore jPBC has been benchmarked on different Android mobile platforms.