On the semantics of communications when verifying equivalence properties

International audienceSymbolic models for security protocol verification were pioneered by Dolev and Yao in their seminal work. Since then, although inspired by the same ideas, many variants of the original model were developed. In particular, a common assumption is that the attacker has complete control over the network and can therefore intercept any message. This assumption has been interpreted in slightly different ways depending on the particular models: either any protocol output is directly routed to the adversary, or communications may be among any two participants, including the attacker-the scheduling between which exact parties the communication happens is left to the attacker. This difference may seem unimportant at first glance and, depending on the verification tools, either one or the other semantics is implemented. We show that, unsurprisingly, they indeed coincide for reachability properties. However, for indistinguishability properties, we prove that these two interpretations lead to incomparable semantics. We also introduce and study a new semantics, where internal communications are allowed but messages are always eavesdropped by the attacker. This new semantics yields strictly stronger equivalence relations. Moreover, we identify two subclasses of protocols for which the three semantics coincide. Finally, we implemented verification of trace equivalence for each of the three semantics in the DeepSec tool and compare their performances on several classical examples

On communication models when verifying equivalence properties (extended version)

International audienceSymbolic models for security protocol verification, following the sem-inal ideas of Dolev and Yao, come in many flavors, even though they share the same ideas. A common assumption is that the attacker has complete control over the network: he can therefore intercept any message. Depending on the precise model this may be reflected either by the fact that any protocol output is directly routed to the adversary, or communications may be among any two participants, including the attacker — the scheduling between which exact parties the communication happens is left to the attacker. These two models may seem equivalent at first glance and, depending on the verification tools, either one or the other semantics is implemented. We show that, unsurprisingly, they indeed coincide for reachability properties. However, when we consider indistinguishability properties, we prove that these two semantics are incomparable. We also introduce a new semantics, where internal communications are allowed but messages are always eavesdropped by the attacker. We show that this new semantics yields strictly stronger equivalence relations. We also identify two subclasses of protocols for which the three semantics coincide. Finally, we implemented verification of trace equivalence for each of these semantics in the APTE tool and compare their performances on several classical examples

On communication models when verifying equivalence properties

International audienceSymbolic models for security protocol verification, following the sem-inal ideas of Dolev and Yao, come in many flavors, even though they share the same ideas. A common assumption is that the attacker has complete control over the network: he can therefore intercept any message. Depending on the precise model this may be reflected either by the fact that any protocol output is directly routed to the adversary, or communications may be among any two participants, including the attacker — the scheduling between which exact parties the communication happens is left to the attacker. These two models may seem equivalent at first glance and, depending on the verification tools, either one or the other semantics is implemented. We show that, unsurprisingly, they indeed coincide for reachability properties. However, when we consider indistinguishability properties, we prove that these two semantics are incomparable. We also introduce a new semantics, where internal communications are allowed but messages are always eavesdropped by the attacker. We show that this new semantics yields strictly stronger equivalence relations. We also identify two subclasses of protocols for which the three semantics coincide. Finally, we implemented verification of trace equivalence for each of these semantics in the APTE tool and compare their performances on several classical examples

Mysticeti: Low-Latency DAG Consensus with Fast Commit Path

We introduce Mysticeti-C a byzantine consensus protocol with low-latency and high resource efficiency. It leverages a DAG based on Threshold Clocks and incorporates innovations in pipelining and multiple leaders to reduce latency in the steady state and under crash failures. Mysticeti-FPC incorporates a fast commit path that has even lower latency. We prove the safety and liveness of the protocols in a byzantine context. We evaluate Mysticeti and compare it with state-of-the-art consensus and fast path protocols to demonstrate its low latency and resource efficiency, as well as more graceful degradation under crash failures. Mysticeti is the first byzantine protocol to achieve WAN latency of 0.5s for consensus commit, at a throughput of over 50k TPS that matches the state-of-the-art

SHORTSTACK : Distributed, Fault-tolerant, Oblivious Data Access

Many applications that benefit from data offload to cloud services operate on private data. A now-long line of work has shown that, even when data is offloaded in an encrypted form, an adversary can learn sensitive information by analyzing data access patterns. Existing techniques for oblivious data access—that protect against access pattern attacks—require a centralized and stateful trusted proxy to orchestrate data accesses from applications to cloud services. We show that, in failure-prone deployments, such a centralized and stateful proxy results in violation of oblivious data access security guarantees and/or in system unavailability. We thus initiate the study of distributed, fault-tolerant, oblivious data access. We present SHORTSTACK , a distributed proxy architecture for oblivious data access in failure-prone deployments. SHORTSTACK achieves the classical obliviousness guarantee—access patterns observed by the adversary being independent of the input—even under a powerful passive persistent adversary that can force failure of arbitrary (bounded-sized) subset of proxy servers at arbitrary times. We also introduce a security model that enables studying oblivious data access with distributed, failure-prone, servers. We provide a formal proof that SHORTSTACK enables oblivious data access under this model, and show empirically that SHORTSTACK performance scales near-linearly with number of distributed proxy servers

Clockwork Finance: Automated Analysis of Economic Security in Smart Contracts

We introduce the Clockwork Finance Framework (CFF), a general purpose, formal verification framework for mechanized reasoning about the economic security properties of composed decentralized-finance (DeFi) smart contracts. CFF features three key properties. It is contract complete, meaning that it can model any smart contract platform and all its contracts—Turing complete or otherwise. It does so with asymptotically constant model overhead. It is also attack-exhaustive by construction, meaning that it can automatically and mechanically extract all possible economic attacks on users’ cryptocurrency across modeled contracts. Thanks to these properties, CFF can support multiple goals: economic security analysis of contracts by developers, analysis of DeFi trading risks by users, fees UX, and optimization of arbitrage opportunities by bots or miners. Because CFF offers composability, it can support these goals with reasoning over any desired set of potentially interacting smart contract models. We instantiate CFF as an executable model for Ethereum contracts that incorporates a state-of-the-art deductive verifier. Building on previous work, we introduce extractable value (EV), a new formal notion of economic security in composed DeFi contracts that is both a basis for CFF and of general interest. We construct modular, human-readable, composable CFF models of four popular, deployed DeFi protocols in Ethereum: Uniswap, Uniswap V2, Sushiswap, and MakerDAO, representing a combined 24 billion USD in value as of March 2022. We use these models along with some other common models such as flash loans, airdrops and voting to show experimentally that CFF is practical and can drive useful, data-based EV-based insights from real world transaction activity. Without any explicitly programmed attack strategies, CFF uncovers on average an expected $56 million of EV per month in the recent past

Complete Knowledge: Preventing Encumbrance of Cryptographic Secrets

Most cryptographic protocols model a player’s knowledge of secrets in a simple way. Informally, the player knows a secret in the sense that she can directly furnish it as a (private) input to a protocol, e.g., to digitally sign a message. The growing availability of Trusted Execution Environments (TEEs) and secure multiparty computation, however, undermines this model of knowledge. Such tools can encumber a secret sk and permit a chosen player to access sk conditionally, without actually knowing sk. By permitting selective access to sk by an adversary, encumbrance of secrets can enable vote-selling in cryptographic voting schemes, illegal sale of credentials for online services, and erosion of deniability in anonymous messaging systems. Unfortunately, existing proof-of-knowledge protocols fail to demonstrate that a secret is unencumbered. We therefore introduce and formalize a new notion called complete knowledge (CK). A proof (or argument) of CK shows that a prover does not just know a secret, but also has fully unencumbered knowledge, i.e., unrestricted ability to use the secret. We introduce two practical CK schemes that use special-purpose hardware, specifically TEEs and off-the-shelf mining ASICs. We prove the security of these schemes and explore their practical deployment with a complete, end-to-end prototype that supports both. We show how CK can address encumbrance attacks identified in previous work. Finally, we introduce two new applications enabled by CK that involve proving ownership of blockchain assets