In recent years, many blockchain systems have progressively transitioned to proof-of-stake (PoS) con- sensus algorithms. These algorithms are not only more energy efficient than proof-of-work but are also well-studied and widely accepted within the community. However, PoS systems are susceptible to a particularly powerful "long-range" attack, where an adversary can corrupt the validator set retroactively and present forked versions of the blockchain. These versions would still be acceptable...

Fully Homomorphic encryption allows the evaluation of any circuits over encrypted data while preserving the privacy of the data. However, without any additional properties, no guarantee is provided for the privacy of the circuits which are evaluated. A sanitization algorithm allows to destroy all previous information about how a ciphertext was obtained, ensuring that the circuit which was evaluated remains secret. In this paper, we present two techniques to randomize RLWE ciphertexts, and...

Differential privacy (DP) is a key tool in privacy-preserving data analysis. Yet it remains challenging for non-privacy-experts to prove the DP of their algorithms. We propose a methodology for domain experts with limited data privacy background to empirically estimate the privacy of an arbitrary mechanism. Our Eureka moment is a new link---which we prove---between the problems of DP parameter-estimation and Bayes optimal classifiers in ML, which we believe can be of independent interest....

The offline-online model is a leading paradigm for practical secure multi-party computation (MPC) protocol design that has successfully reduced the overhead for several prevalent privacy-preserving computation functionalities common to diverse application domains. However, the prohibitive overheads associated with secure comparison -- one of these vital functionalities -- often bottlenecks current and envisioned MPC solutions. Indeed, an efficient secure comparison solution has the potential...

Implantable Medical Devices (IMDs) are widely deployed today and often use wireless communication. Establishing a secure communication channel to these devices is vital, however, also challenging in practice. To address this issue, numerous researchers have proposed IMD key exchange protocols, in particular ones that leverage an Out-Of-Band (OOB) channel such as audio, vibration and physiological signals. These solutions have advantages over traditional key exchange, e.g.,...

Homomorphic encryption (HE) is a promising technology for protecting data in use, with considerable recent years progress towards attaining practical runtime performance. However the high storage overhead associated with HE remains an obstacle preventing its large scale adoption. In this work we propose a new storage solution in the two-server model resolving the high storage overhead associated with HE, while preserving data confidentiality. Our solution attains the following desired...

Wireless radio channels are known to contain information about the surrounding propagation environment, which can be extracted using established wireless sensing methods. Thus, today's ubiquitous wireless devices are attractive targets for passive eavesdroppers to launch reconnaissance attacks. In particular, by overhearing standard communication signals, eavesdroppers obtain estimations of wireless channels which can give away sensitive information about indoor environments. For instance,...

We propose Manta, a plug and play private DeFi stack that consists of MantaDAP, a multi-asset decentralized anonymous payment scheme and MantaDAX, an automated market maker(AMM) based decentralized anonymous exchange scheme. Compared with existing privacy preserving cryptocurrencies such as Zcash and Monero,Manta supports multiple base assets and allows the privatized assets to be exchanged anonymously via MantaDAX. We think this is a major step forward towards building a privacy preserving...

Sigma-Protocols provide a well-understood basis for secure algorithmics. Recently, Bulletproofs (Bootle et al., EUROCRYPT 2016, and Bünz et al., S&P 2018) have been proposed as a drop-in replacement in case of zero-knowledge (ZK) for arithmetic circuits, achieving logarithmic communication instead of linear. Its pivot is an ingenious, logarithmic-size proof of knowledge BP for certain quadratic relations. However, reducing ZK for general relations to it forces a somewhat cumbersome ...

We consider the problem of proving in zero knowledge that an element of a public set satisfies a given property without disclosing the element, i.e., for some $u$, ``$u \in S$ and $P(u)$ holds''. This problem arises in many applications (anonymous cryptocurrencies, credentials or whitelists) where, for privacy or anonymity reasons, it is crucial to hide certain data while ensuring properties of such data. We design new \textit{modular} and \textit{efficient} constructions for this problem...

Security and safety-critical remote applications such as e-voting, online banking, industrial control systems and medical devices rely upon user interaction that is typically performed through web applications. Trusted path to such remote systems is critical in the presence of an attacker that controls the computer that the user operates. Such an attacker can observe and modify any IO data without being detected by the user or the server. We investigate the security of previous research...

Various safety-critical devices, such as industrial control systems, medical devices, and home automation systems, are configured through web interfaces from remote hosts that are standard PCs. The communication link from the host to the safety-critical device is typically easy to protect, but if the host gets compromised, the adversary can manipulate any user-provided configuration settings with severe consequences including safety violations. In this paper, we propose IntegriKey, a novel...

Privacy-enhancing attribute-based credentials (PABCs) are the core ingredient to privacy-friendly authentication systems, allowing users to obtain credentials on attributes and prove possession of these credentials in an unlinkable fashion while revealing only a subset of the attributes. To be useful in practice, however, PABCs typically need additional features such as i) revocation, ii) pooling prevention by binding credentials to users' secret keys, iii) pseudonyms as privacy-friendly...

We present the Plug-and-Play IP Security (PnP-IPsec) protocol. PnP-IPsec automatically establishes IPsec security associations between gateways, avoiding the need for manual administration and coordination between gateways, and the dependency on IPsec public key certificates - the two problems which are widely believed to have limited the use of IPsec mostly to intra-organization communication. PnP-IPsec builds on Self-validated Public Data Distribution (SvPDD), a protocol that we present...