Tight Mobile Byzantine Tolerant Atomic Storage

This paper proposes the first implementation of an atomic storage tolerant to mobile Byzantine agents. Our implementation is designed for the round-based synchronous model where the set of Byzantine nodes changes from round to round. In this model we explore the feasibility of multi-writer multi-reader atomic register prone to various mobile Byzantine behaviors. We prove upper and lower bounds for solving the atomic storage in all the explored models. Our results, significantly different from the static case, advocate for a deeper study of the main building blocks of distributed computing while the system is prone to mobile Byzantine failures

Threshold FlipThem:when the winner does not need to take all

We examine a FlipIt game in which there are multiple resources which a monolithic attacker is trying to compromise. This extension to FlipIt was considered in a paper in GameSec 2014, and was there called FlipThem. Our analysis of such a situation is focused on the situation where the attacker’s goal is to compromise a threshold of the resources. We use our game theoretic model to enable a defender to choose the correct configuration of resources (number of resources and the threshold) so as to ensure that it makes no sense for a rational adversary to try to attack the system. This selection is made on the basis of the relative costs of the attacker and the defender

Provably Secure Virus Detection: Using The Observer Effect Against Malware

Protecting software from malware injection is one of the biggest challenges of modern computer science. Despite intensive efforts by the scientific and engineering community, the number of successful attacks continues to increase. This work sets first footsteps towards a provably secure investigation of malware detection. We provide a formal model and cryptographic security definitions of attestation for systems with dynamic memory, and suggest novel provably secure attestation schemes. The key idea underlying our schemes is to use the very insertion of the malware itself to allow for the systems to detect it. This is, in our opinion, close in spirit to the quantum Observer Effect. The attackers, no matter how clever, no matter when they insert their malware, change the state of the system they are attacking. This fundamental idea can be a game changer. And our system does not rely on heuristics; instead, our scheme enjoys the unique property that it is proved secure in a formal and precise mathematical sense and with minimal and realistic CPU modification achieves strong provable security guarantees. We envision such systems with a formal mathematical security treatment as a venue for new directions in software protection

Authenticating compromisable storage systems

A service may be implemented over several servers, and those servers may become compromised by an attacker, e.g. through software vulnerabilities. When this happens, the service manager will remove the vulnerabilities and re-instate the server. Typically, this will involve regenerating the public key by which clients authenticate the service, and revoking the old one. This paper presents a scheme which allows a storage service composed of several servers to create a group public key in a decentralised manner, and maintain its security even when such compromises take place. By maintaining keys for a long term, we reduce the reliance on public-key certification. The storage servers periodically update the decryption secrets corresponding to a public key, in such a way that secrets gained by an attacker are rendered useless after an update takes place. An attacker would have to compromise all the servers within a short period lying between two updates in order to fully compromise the system

A Two-Party Hierarchical Deterministic Wallets in Practice

The applications of Hierarchical Deterministic Wallet are rapidly growing in various areas such as cryptocurrency exchanges and hardware wallets. Improving privacy and security is more important than ever. In this study, we proposed a protocol that fully support a two-party computation of BIP32. Our protocol, similar to the distributed key generation, can generate each party’s secret share, the common chain-code, and the public key without revealing a seed and any descendant private keys. We also provided a simulation-based proof of our protocol assuming a rushing, static, and malicious adversary in the hybrid model. Our master key generation protocol produces up to total of two bit leakages from a honest party given the feature that the seeds will be re-selected after each execution. The proposed hardened child key derivation protocol leads up to a one bit leakage in the worst situation of simulation from a honest party and will be accumulated with each execution. Fortunately, in reality, this issue can be largely mitigated by adding some validation criteria of boolean circuits and masking the input shares before each execution. We then implemented the proposed protocol and ran in a single thread on a laptop which turned out with practically acceptable execution time. Lastly, the outputs of our protocol can be easily integrated with many threshold sign protocols

Asynchronous distributed private-key generators for identity-based cryptography

An identity-based encryption (IBE) scheme can greatly reduce the complexity of sending encrypted messages over the Internet. However, an IBE scheme necessarily requires a private-key generator (PKG), which can create private keys for clients, and so can passively eavesdrop on all encrypted communications. Although a distributed PKG has been suggested as a way to mitigate this problem for Boneh and Franklin’s IBE scheme, the security of this distributed protocol has not been proven and the proposed solution does not work over the asynchronous Internet. Further, a distributed PKG has not been considered for any other IBE scheme. In this paper, we design distributed PKG setup and private key extraction protocols in an asynchronous communication model for three important IBE schemes; namely, Boneh and Franklin’s IBE, Sakai and Kasahara’s IBE, and Boneh and Boyen’s BB1-IBE. We give special attention to the applicability of our protocols to all possible types of bilinear pairings and prove their IND-ID-CCA security in the random oracle model. Finally, we also perform a comparative analysis of these protocols and present recommendations for their use.

On the Resilience of Intrusion-Tolerant Distributed Systems

The paper starts by introducing a new dimension along which distributed systems resilience may be evaluated - exhaustion-safety. A node-exhaustion-safe intrusion-tolerant distributed system is a system that assuredly does not suffer more than the assumed number of node failures (e.g., crash, Byzantine). We show that it is not possible to build this kind of systems under the asynchronous model. This result follows from the fact that in an asynchronous environment one cannot guarantee that the system terminates its execution before the occurrence of more than the assumed number of faults. After introducing exhaustion-safety, the paper proposes a new paradigm - proactive resilience - to build intrusion-tolerant distributed systems. Proactive resilience is based on architectural hybridization and hybrid distributed system modeling. The Proactive Resilience Model (PRM) is presented and shown to be a way of building node-exhaustion-safe intrusion-tolerant systems. Finally, the paper describes the design of a secret sharing system built according to the PRM. A proof-of-concept prototype of this system is shown to be highly resilient under different attack scenarios

DyCAPS: Asynchronous Dynamic-committee Proactive Secret Sharing

Dynamic-committee proactive secret sharing (DPSS) enables the refresh of secret shares and the alternation of shareholders without changing the secret. Such a proactivization functionality makes DPSS a promising technology for long-term key management and committee governance. In non-asynchronous networks, CHURP (CCS ’19) and COBRA (S&P ’22) have achieved best-case square and cubic communication cost, respectively, w.r.t. the number of shareholders. However, the overhead of asynchronous DPSS remains high. This gap hinders asynchronous protocols from evolving to the dynamic setting, such as BFT systems and threshold cryptography services. In this paper, we fill this gap and propose DyCAPS, an efficient asynchronous DPSS protocol with a cubic communication cost. DyCAPS supports the transfer of both low- and high-threshold secret shares among dynamic committees with the same communication and computation complexity. Experimental results show that proactivization between two disjoint committees of 4 (resp., 64) members takes 1.3 (resp., 51) seconds. Moreover, DyCAPS is designed to be compatible with asynchronous BFT protocols without increasing the asymptotic communication cost. Given a payload of 5–10 MB per node, DyCAPS achieves member change in Dumbo2 (CCS ’20) at around 10% temporary throughput degradation, with the committee size varying from 4 to 22