Distributed randomness beacon protocols, which continuously generate publicly verifiable randomness values, are crucial for many applications. Recently, there have been many approaches, such as Hydrand (S\&P'20), SPURT (S\&P'22), OptRand (NDSS'23) and GRandLine (CCS'24), based on publicly verifiable secret sharing (PVSS) to implement beacon protocols. However, two key challenges remain unresolved: asynchrony and reconfiguration. In this paper, we propose the $\mathsf{AsyRand}$ beacon...

Threshold signatures have become a critical tool in cryptocurrency systems, offering enhanced security by distributing the signing process among multiple signers. In this work, we distribute this process between a client and a permissionless decentralized blockchain, and present novel protocols for ECDSA and EdDSA/Schnorr signatures in this setting. Typical threshold access architectures used by trusted custodians suffer from the honeypot problem, wherein the more assets the custodian holds,...

In this paper, we study practical constructions of asynchronous distributed key reconfiguration ($\mathsf{ADKR}$), which enables an asynchronous fault-tolerant system with an existing threshold cryptosystem to efficiently generate a new threshold cryptosystem for a reconfigured set of participants. While existing asynchronous distributed threshold key generation ($\mathsf{ADKG}$) protocols theoretically solve $\mathsf{ADKR}$, they fail to deliver satisfactory scalability due to cubic...

Sharding emerges as a promising solution to enhance blockchain scalability. However, it faces two critical limitations during shard reconfiguration: (1) the TPS-Degradation issue, arising from ledger synchronization conflicts during transaction processing, and (2) the Zero-TPS issue, caused by disruptions in transaction processing due to key negotiation. To this end, we propose Shardora, a blockchain sharding system for scaling blockchain by unleashing parallelism. In Shardora, we implement...

In this article, we propose a generic hybrid encryption scheme providing entity authentication. The scheme is based on lossy trapdoor functions relying on the hardness of the Learning With Errors problem. The construction can be used on a number of different security requirements with minimal reconfiguration. It ensures entity authentication and ciphertext integrity while providing security against adaptive chosen ciphertext attacks in the standard model. As a desired characteristic of...

We present Rondo, a scalable and reconfiguration-friendly distributed randomness beacon (DRB) protocol in the partially synchronous model. Rondo is the first DRB protocol that is built from batched asynchronous verifiable secret sharing (bAVSS) and meanwhile avoids the high $O(n^3)$ message cost, where $n$ is the number of nodes. Our key contribution lies in the introduction of a new variant of bAVSS called batched asynchronous verifiable secret sharing with partial output (bAVSS-PO)....

This paper introduces Nimble, a cloud service that helps applications running in trusted execution environments (TEEs) to detect rollback attacks (i.e., detect whether a data item retrieved from persistent storage is the latest version). To achieve this, Nimble realizes an append-only ledger service by employing a simple state machine running in a TEE in conjunction with a crash fault-tolerant storage service. Nimble then replicates this trusted state machine to ensure the system is...

Secure computation is of critical importance to not only the DoD, but across financial institutions, healthcare, and anywhere personally identifiable information (PII) is accessed. Traditional security techniques require data to be decrypted before performing any computation. When processed on untrusted systems the decrypted data is vulnerable to attacks to extract the sensitive information. To address these vulnerabilities Fully Homomorphic Encryption (FHE) keeps the data encrypted...

This paper studies dynamic BFT, where replicas can join and leave the system dynamically, a primitive that is nowadays increasingly needed. We provide a formal treatment for dynamic BFT protocols, endowing them with a flexible syntax and various security definitions. We demonstrate the challenges of extending static BFT to dynamic BFT. Then we design and implement Dyno, a highly efficient dynamic BFT protocol under the partial synchrony model. We show that Dyno can seamlessly handle...

Public random beacons publish random numbers at regular intervals, which anyone can obtain and verify. The design of public distributed random beacons has been an exciting research direction with significant implications for blockchains, voting, and beyond. Distributed random beacons, in addition to being bias-resistant and unpredictable, also need to have low communication overhead and latency, high resilience to faults, and ease of reconfigurability. Existing synchronous random beacon...

Abstract—CARiMoL is a novel run-time Configurable Hardware Accelerator for Ring and Module Lattice-based postquantum cryptography. It’s flexible design can be configured to key-pair generation, encapsulation, and decapsulation for NewHope and CRYSTALS-Kyber schemes using same hardware. CARiMoL offers run-time configurability for multiple security levels of NewHope and CRYSTALS-Kyber schemes, supporting both Chosen-Plaintext Attack (CPA) and Chosen-Ciphertext Attack (CCA) secure...

Random beacon protocols provide a continuous public source of randomness and their applications range from public lotteries to zero-knowledge proofs. Existing random beacon protocols in the bounded synchronous model sacrifice either the fault tolerance or the communication complexity for security, or ease of reconfigurability. This work overcomes the challenges with the existing works through a novel communication efficient combination of state machine replication and (publicly) verifiable...

Secure Elements (SEs) are hardware trust anchors which provide cryptographic services including secure storage of secret keys and certificates. In long-living devices certain cryptographic functions might get insecure over time, e.g. new implementation attacks or bugs are discovered, and might require to be updated. On FPGAs, partial reconfiguration (PR) offers the opportunity to overcome this issue by replacing buggy or outdated hardware on the fly. This work provides an architecture for an...

In today’s Integrated Circuit (IC) production chains, a designer’s valuable Intellectual Property (IP) is transparent to diverse stakeholders and thus inevitably prone to piracy. To protect against this threat, numerous defenses based on the obfuscation of a circuit’s control path, i.e. Finite State Machine (FSM), have been proposed and are commonly believed to be secure. However, the security of these sequential obfuscation schemes is doubtful since realistic capabilities of reverse...

Dynamic and partial reconfiguration together with hardware parallelism make FPGAs attractive as virtualized accelerators. However, recently it has been shown that multi-tenant FPGAs are vulnerable to remote side-channel attacks (SCA) from malicious users, allowing them to extract secret keys without a logical connection to the victim core. Typical mitigations against such attacks are hiding and masking schemes, to increase attackers’ efforts in terms of side-channel measurements. However,...

Field-Programmable Gate Arrays or FPGAs are popular platforms for hardware-based attestation. They offer protection against physical and remote attacks by verifying if an embedded processor is running the intended application code. However, since FPGAs are configurable after deployment (thus not tamper-resistant), they are susceptible to attacks, just like microprocessors. Therefore, attesting an electronic system that uses an FPGA should be done by verifying the status of both the software...

A major approach to overcoming the performance and scalability limitations of current blockchain protocols is to use sharding, which is to split the overheads of processing transactions among multiple, smaller groups of nodes. These groups work in parallel to maximize performance while requiring significantly smaller communication, computation, and storage per node, allowing the system to scale to large networks. However, existing sharding-based blockchain protocols still require a linear...

Recent literature has demonstrated that the security of Physically Unclonable Function (PUF) circuits might be adversely affected by the introduction of faults. In this paper, we propose novel and efficient architectures for a variety of widely used delay-based PUFs which are robust against high precision laser fault attacks proposed by Tajik et al. in FDTC-2015. The proposed architectures can be used to detect run-time modifications in the PUF design due to fault injection. In addition, we...

Reconfigurability is a unique feature of modern FPGA devices to load hardware circuits just on demand. This also implies that a completely different set of circuits might operate at the exact same location of the FPGA at different time slots, making it difficult for an external observer or attacker to predict what will happen at what time. In this work we present and evaluate a novel hardware implementation of the lightweight cipher PRESENT with built-in side-channel countermeasures based on...

Block Memory Content Scrambling (BMS), presented at CHES 2011, enables an effective way of first-order side-channel protection for cryptographic primitives at the cost of a significant reconfiguration time for the mask update. In this work we analyze alternative ways to implement dynamic first-order masking of AES with randomized look-up tables that can reduce this mask update time. The memory primitives we consider in this work include three distributed RAM components (RAM32M, RAM64M, and...