We present Path ORAM, an extremely simple Oblivious RAM protocol with a small amount of client storage. Partly due to its simplicity, Path ORAM is the most practical ORAM scheme for small client storage known to date. We formally prove that Path ORAM requires log^2 N / log X bandwidth overhead for block size B = X log N. For block sizes bigger than Omega(log^2 N), Path ORAM is asymptotically better than the best known ORAM scheme with small client storage. Due to its practicality, Path ORAM has been adopted in the design of secure processors since its proposal.

/pdf/path-oram-an-extremely-simple-oblivious-ram-protocol-3wxilo1971.pdf

Path ORAM: an extremely simple oblivious RAM protocol

We present HotStuff, a leader-based Byzantine fault-tolerant replication protocol for the partially synchronous model. Once network communication becomes synchronous, HotStuff enables a correct leader to drive the protocol to consensus at the pace of actual (vs. maximum) network delay--a property called responsiveness---and with communication complexity that is linear in the number of replicas. To our knowledge, HotStuff is the first partially synchronous BFT replication protocol exhibiting these combined properties. Its simplicity enables it to be further pipelined and simplified into a practical, concise protocol for building large-scale replication services.

https://dl.acm.org/doi/pdf/10.1145/3293611.3331591

HotStuff: BFT Consensus with Linearity and Responsiveness

LSB: A Lightweight Scalable Blockchain for IoT security and anonymity

We present Path ORAM, an extremely simple Oblivious RAM protocol with a small amount of client storage. Partly due to its simplicity, Path ORAM is the most practical ORAM scheme known to date with small client storage. We formally prove that Path ORAM has a O(log N) bandwidth cost for blocks of size B = Ω (log2N) bits. For such block sizes, Path ORAM is asymptotically better than the best-known ORAM schemes with small client storage. Due to its practicality, Path ORAM has been adopted in the design of secure processors since its proposal.

Path ORAM: An Extremely Simple Oblivious RAM Protocol

We design and build ObliviStore, a high performance, distributed ORAM-based cloud data store secure in the malicious model. To the best of our knowledge, ObliviStore is the fastest ORAM implementation known to date, and is faster by 10X or more in comparison with the best known ORAM implementation. ObliviStore achieves high throughput by making I/O operations asynchronous. Asynchrony introduces security challenges, i.e., we must prevent information leakage not only through access patterns, but also through timing of I/O events. We propose various practical optimizations which are key to achieving high performance, as well as techniques for a data center to dynamically scale up a distributed ORAM. We show that with 11 trusted machines (each with a modern CPU), and 20 Solid State Drives, ObliviStore achieves a throughput of 31.5MB/s with a block size of 4KB.

/pdf/oblivistore-high-performance-oblivious-cloud-storage-26fdffpybe.pdf

ObliviStore: High Performance Oblivious Cloud Storage

SBFT is a state of the art Byzantine fault tolerant permissioned blockchain system that addresses the challenges of scalability, decentralization and world-scale geo-replication. SBFTis optimized for decentralization and can easily handle more than 200 active replicas in a real world-scale deployment. We evaluate \sysname in a world-scale geo-replicated deployment with 209 replicas withstanding f=64 Byzantine failures. We provide experiments that show how the different algorithmic ingredients of \sysname increase its performance and scalability. The results show that SBFT simultaneously provides almost 2x better throughput and about 1.5x better latency relative to a highly optimized system that implements the PBFT protocol. To achieve this performance improvement, SBFT uses a combination of four ingredients: using collectors and threshold signatures to reduce communication to linear, using an optimistic fast path, reducing client communication and utilizing redundant servers for the fast path.

SBFT: a Scalable and Decentralized Trust Infrastructure

PrivateFS is an oblivious file system that enables access to remote storage, while keeping both the file contents and client access patterns secret. PrivateFS is based on a new parallel Oblivious RAM mechanism (PD-ORAM)---instead of waiting for the completion of all ongoing client-server transactions, client threads can now engage a server in parallel without loss of privacy.This critical piece is missing from existing Oblivious RAMs (ORAM), which can not allow multiple clients threads to operate simultaneously without revealing intra- and inter-query correlations and thus incurring privacy leaks. And since ORAMs often require many communication rounds, this significantly and unnecessarily constrains throughput.The mechanisms introduced here eliminate this constraint, allowing overall throughput to be bound by server bandwidth only, and thus to increase by an order of magnitude. Further, new de-amortization techniques bring the worst case query cost in line with the average cost. Both of these results are shown to be fundamental to any ORAM. Extensions providing fork consistency against an actively malicious adversary are then presented.A high performance, fully functional PD-ORAM implementation was designed, built and analyzed. It performs multiple queries per second on a 1TB+ database across 50ms latency links, with unamortized, bound query latencies. Based on PD-ORAM, PrivateFS was built and deployed on Linux as a userspace file system.

PrivateFS: a parallel oblivious file system

We present Catena, an efficiently-verifiable Bitcoinwitnessing scheme. Catena enables any number of thin clients, such as mobile phones, to efficiently agree on a log of application-specific statements managed by an adversarial server. Catenaimplements a log as an OP_RETURN transaction chain andprevents forks in the log by leveraging Bitcoin's security againstdouble spends. Specifically, if a log server wants to equivocate ithas to double spend a Bitcoin transaction output. Thus, Catenalogs are as hard to fork as the Bitcoin blockchain: an adversarywithout a large fraction of the network's computational powercannot fork Bitcoin and thus cannot fork a Catena log either. However, different from previous Bitcoin-based work, Catenadecreases the bandwidth requirements of log auditors from 90GB to only tens of megabytes. More precisely, our clients onlyneed to download all Bitcoin block headers (currently less than35 MB) and a small, 600-byte proof for each statement in a block. We implement Catena in Java using the bitcoinj library and use itto extend CONIKS, a recent key transparency scheme, to witnessits public-key directory in the Bitcoin blockchain where it can beefficiently verified by auditors. We show that Catena can securemany systems today, such as public-key directories, Tor directoryservers and software transparency schemes.

https://www.computer.org/csdl/pds/api/csdl/proceedings/download-article/1ap5pmaUkIE/pdf

Catena: Efficient Non-equivocation via Bitcoin

SBFT is a state of the art Byzantine fault tolerant state machine replication system that addresses the challenges of scalability, decentralization and global geo-replication. SBFT is optimized for decentralization and is experimentally evaluated on a deployment of more than 200 active replicas withstanding a malicious adversary controlling f=64 replicas. Our experiments show how the different algorithmic ingredients of SBFT contribute to its performance and scalability. The results show that SBFT simultaneously provides almost 2x better throughput and about 1.5x better latency relative to a highly optimized system that implements the PBFT protocol. To achieve this performance improvement, SBFT uses a combination of four ingredients: using collectors and threshold signatures to reduce communication to linear, using an optimistic fast path, reducing client communication and utilizing redundant servers for the fast path. SBFT is the first system to implement a correct dual-mode view change protocol that allows to efficiently run either an optimistic fast path or a fallback slow path without incurring a view change to switch between modes.

SBFT: A Scalable and Decentralized Trust Infrastructure

We present SBFT: a scalable decentralized trust infrastructure for Blockchains. SBFT implements a new Byzantine fault tolerant algorithm that addresses the challenges of scalability and decentralization. Unlike many previous BFT systems that performed well only when centralized around less than 20 replicas, SBFT is optimized for decentralization and can easily handle more than 100 active replicas. SBFT provides a smart contract execution environment based on Ethereum's EVM byte-code. 
We tested SBFT by running 1 million EVM smart contract transactions taken from a 4-month real-world Ethereum workload. In a geo-replicated deployment that has about 100 replicas and can withstand $f=32$ Byzantine faults our system shows speedups both in throughput and in latency. SBFT completed this execution at a rate of 50 transactions per second. This is a $10\times$ speedup compared to Ethereum current limit of $5$ transactions per second. SBFT latency to commit a smart contract execution and make it final is sub-second, this is more than $10\times$ speedup compared to Ethereum current $>15$ second block generation for registering a smart contract execution and several orders of magnitude speedup relative to Proof-of-Work best-practice finality latency of one-hour.

Alin Tomescu

Papers

SBFT: a Scalable and Decentralized Trust Infrastructure

PrivateFS: a parallel oblivious file system

Catena: Efficient Non-equivocation via Bitcoin

SBFT: A Scalable and Decentralized Trust Infrastructure

SBFT: a Scalable Decentralized Trust Infrastructure for Blockchains.