Beyond Trust: Building Resilient Ledgers for Imperfect Hardware

Author: Denis Avetisyan

A new approach, Proteus, blends the speed of simpler consensus with the robust security of Byzantine Fault Tolerance to create ledgers that can withstand compromise in Trusted Execution Environments.

Proteus combines Crash Fault Tolerance and Byzantine Fault Tolerance via an embedded audit protocol, offering strong integrity guarantees for append-only ledgers within TEEs.

While distributed ledgers increasingly rely on Trusted Execution Environments (TEEs) to bolster data integrity and availability, these hardware-based safeguards are not invulnerable, creating a critical vulnerability for systems demanding high assurance. Addressing this paradox, we introduce ‘Proteus: Append-Only Ledgers for (Mostly) Trusted Execution Environments’, a novel consensus protocol that cautiously integrates Byzantine Fault Tolerance (BFT) within a Crash Fault Tolerant (CFT) framework-without increasing message complexity. This approach embeds an audit layer within the standard commit process, guaranteeing ledger integrity even in the event of TEE compromise. Could this careful alignment of CFT and BFT protocols represent a new paradigm for platform-fault-tolerant distributed systems?

The Challenge of Trust in a Hostile Landscape

Conventional distributed consensus protocols, such as those underpinning many blockchain and database systems, historically operate on the premise of largely trustworthy nodes – a significant limitation in increasingly complex and adversarial digital environments. These systems frequently assume a majority of participating nodes will act honestly, making them acutely vulnerable if a substantial portion of the infrastructure falls under compromise – whether through malicious attacks, software vulnerabilities, or internal malfeasance. This reliance on inherent trustworthiness creates a single point of failure, as a determined attacker gaining control of a sufficient number of nodes can manipulate the consensus process and compromise the integrity of the entire system. Consequently, modern research increasingly focuses on designing protocols that minimize trust assumptions and prioritize resilience against platform compromises, acknowledging that complete security cannot be guaranteed through node trustworthiness alone.

The pursuit of dependable distributed consensus necessitates a shift beyond simply assuming node integrity; instead, systems must actively verify and enforce accountability amongst participants. Traditional methods falter when faced with adversarial behavior, prompting research into novel techniques like cryptographic attestation and zero-knowledge proofs. These approaches allow nodes to prove the correctness of their computations without revealing sensitive data, fostering trust even in untrusted environments. Furthermore, mechanisms for identifying and penalizing malicious actors – such as stake-based systems or reputation scores – are crucial for deterring bad behavior and ensuring the long-term stability of the network. Ultimately, robust consensus in the face of malice demands a proactive stance on verification and a commitment to holding participants accountable for their actions, paving the way for more resilient and secure distributed systems.

Byzantine Fault Tolerance (BFT) protocols, while theoretically capable of achieving consensus even with malicious actors, often present significant computational hurdles in real-world applications. The core of many BFT algorithms involves all nodes communicating with each other to verify the validity of proposed blocks or transactions; this all-to-all communication scales poorly with increasing network size. Specifically, the message complexity typically grows quadratically – meaning doubling the number of nodes requires four times the communication overhead. This exponential increase in computational demands translates directly into slower transaction speeds, higher energy consumption, and increased hardware requirements, effectively limiting the scalability and practical deployment of BFT-based systems. Consequently, researchers are actively exploring techniques to reduce this computational burden, such as employing efficient cryptographic primitives and optimizing communication patterns, to make BFT protocols viable for large-scale distributed systems.

The integration of Trusted Execution Environments (TEEs) presents a promising, yet nuanced, path toward bolstering the security of distributed systems, but requires careful consideration to avoid concentrating new vulnerabilities. While TEEs – secure enclaves within a processor – can isolate critical computations and verify their integrity, over-reliance introduces systemic risks; a compromised TEE manufacturer, or a vulnerability within the TEE itself, could undermine the entire system. Consequently, research focuses on protocols that cautiously leverage TEEs for specific, limited functions – such as verifying signatures or random number generation – rather than entrusting them with complete state management. This approach seeks to minimize the ‘blast radius’ of a potential TEE compromise, and necessitates designs that combine TEE-based verification with traditional cryptographic techniques and robust replication strategies, ensuring that security isn’t solely dependent on the integrity of a single hardware component.

Proteus: A Pragmatic Approach to Consensus

Proteus is a distributed consensus protocol that incorporates Trusted Execution Environments (TEEs) as a component of its security model, but does not rely on complete trust in them. The protocol leverages the isolation capabilities of TEEs to protect sensitive data and cryptographic keys during the consensus process. However, recognizing potential vulnerabilities within TEE implementations, Proteus is designed to limit the scope of trust granted to these environments. This cautious approach involves employing techniques to verify the integrity of TEE-executed code and to mitigate the impact of potential TEE compromises, ensuring the overall system remains secure even if a TEE is subject to attack or malfunction. This strategy aims to benefit from the performance advantages offered by TEEs without incurring the full risk associated with unconditional trust.

Proteus employs a layered consensus architecture, integrating a Byzantine Fault Tolerance (BFT) inner core with an outer Crash Fault Tolerance (CFT) layer. The BFT component addresses scenarios where nodes may exhibit arbitrary, malicious behavior, ensuring consensus even with compromised participants. Surrounding this is the CFT layer, designed to handle simpler, passive failures such as unexpected shutdowns or network disconnections. This combination results in a system capable of tolerating a broader range of fault models than either BFT or CFT alone, increasing overall system resilience and adaptability to varying network conditions and potential attack vectors. The CFT outer layer effectively manages the BFT component, mitigating performance overhead associated with full BFT operation when not strictly necessary.

Proteus achieves a balance between security and performance by nesting a Byzantine Fault Tolerance (BFT) consensus mechanism within a Crash Fault Tolerance (CFT) outer layer. This architectural decision allows the system to leverage the strong security guarantees of BFT – specifically its resilience against malicious actors – while benefiting from the higher throughput characteristic of CFT protocols. Empirical testing demonstrates a peak transaction processing rate of 345,000 transactions per second (k txn/s), indicating a substantial performance improvement over traditional BFT-only systems and a competitive position within distributed consensus protocols. The CFT layer handles typical operational conditions efficiently, while the embedded BFT component activates only when evidence of malicious behavior is detected, minimizing performance overhead during normal operation.

Proteus achieves tolerance of both malicious and passive failures through its layered architectural design. The inner Byzantine Fault Tolerance (BFT) component safeguards against actively malicious nodes attempting to compromise consensus, while the outer Crash Fault Tolerance (CFT) layer ensures continued operation even in the presence of nodes that fail by simply crashing. This combination results in a system resilient to a broader range of failure modes than either BFT or CFT alone; the CFT layer can tolerate crashes while the BFT layer actively prevents malicious behavior, thereby enhancing the protocol’s overall robustness and reliability in unpredictable distributed environments.

Efficient Verification: Quorum Certificates and Audit Trails

Proteus employs both Commit Quorum Certificates and Audit Quorum Certificates as fundamental components of its transaction verification process. Commit Quorum Certificates directly attest to the ordering and commitment of transactions, providing proof of inclusion in the ledger. Audit Quorum Certificates, distinct from commit proofs, provide verifiable evidence of consensus without necessarily requiring the full transaction history. These certificates are constructed through a quorum of validators, ensuring that a sufficient majority agrees on the validity of the transaction or state. The combined use of these two certificate types allows Proteus to offer robust integrity checks and facilitate efficient auditability, enabling verification of transactions independently of the full transaction chain.

Proteus employs two distinct audit paths for transaction verification: a Fast Audit Path and a Slow Audit Path. The Fast Audit Path prioritizes speed by utilizing a single Quorum Certificate to confirm consensus, suitable for straightforward verification scenarios. When a single certificate is insufficient, such as in cases of network instability or higher assurance requirements, the system transitions to the Slow Audit Path. This path involves gathering and validating multiple quorum certificates, providing a more robust, though comparatively slower, verification process. The implementation of both paths allows Proteus to dynamically adapt to network conditions and security needs, optimizing for both speed and reliability.

Proteus achieves efficient consensus verification through the implementation of two audit paths: a Fast Audit Path and a Slow Audit Path. Benchmarks demonstrate that verification latency using the Fast Audit Path is comparable to that of commit receipts. The Slow Audit Path, utilized in more complex scenarios, introduces a moderate increase in latency, achieving verification times only 1.9 times higher than the Fast Audit Path. This performance is a result of leveraging quorum certificates to minimize the overhead associated with confirming transaction validity and maintaining auditability.

The selection between the Fast and Slow Audit Paths in Proteus is dynamically determined by real-time network conditions and the desired level of transactional assurance. When network latency is low and a sufficient quorum can be rapidly established, the Fast Audit Path is utilized, providing verification comparable to commit receipt times. Conversely, in scenarios with higher latency, network instability, or when a greater degree of confidence in consensus is required – such as for high-value transactions – the system automatically switches to the Slow Audit Path. This path involves additional verification steps, resulting in a slightly increased audit latency of 1.9x compared to the Fast Path, but ensures a more robust and thoroughly validated transaction record.

Hash Chaining: A Pathway to Scalable Consensus

Proteus leverages Hash Chaining as a core mechanism for constructing quorums and facilitating audits without requiring complete network synchronization. This innovative approach links batches of transactions together using cryptographic hashes, creating a chain of data that efficiently represents the transaction history. By verifying only the hashes – rather than the full transaction data – auditors can confirm the integrity of the entire record with significantly reduced computational load and communication overhead. This incremental building of quorums, coupled with asynchronous auditing capabilities, results in a substantial performance boost, allowing Proteus to achieve $88.6%$ of the throughput observed in the Autobahn protocol and demonstrating a pathway to highly scalable and efficient distributed systems.

Proteus leverages a chain of cryptographic hashes to ensure transactional integrity without demanding complete data synchronization for auditing purposes. Each batch of transactions is digitally ‘fingerprinted’ – a unique hash is generated from its contents – and then linked to the hash of the previous batch. This creates a continuous, tamper-evident chain extending back to the very first transaction. Auditors can then efficiently verify the history by starting with the latest hash and iteratively checking its connection to the preceding one; any alteration to a past transaction would immediately break this chain, revealing the compromise. This approach bypasses the need to download and process the entire transaction history, dramatically reducing the computational burden and enabling significantly faster verification times.

The implementation of hash chaining substantially minimizes communication demands during verification processes, leading to markedly improved performance. By consolidating transaction data into linked batches, the protocol circumvents the need for full data synchronization between nodes, dramatically reducing network traffic. Benchmarking reveals that Proteus, utilizing this technique, achieves 88.6% of the transaction throughput attained by Autobahn, a leading competitor, demonstrating a significant advancement in scalability and efficiency. This streamlined verification process not only accelerates auditing but also positions hash chaining as a key component in building high-performance, distributed systems.

The implementation of Hash Chaining within the Proteus protocol directly addresses the challenge of maintaining a continuously growing dataset, enabling efficient data pruning without compromising auditability. By structuring transaction batches as a linked chain of cryptographic hashes, the system can selectively discard older, verified data while retaining a secure and verifiable path back to the most recent state. This capability is crucial for scalability, as it prevents unbounded storage requirements and ensures the network remains performant over time. The process allows nodes to operate with a bounded storage footprint, reducing resource demands and facilitating broader participation in the network, all while maintaining the integrity and verifiability of the historical record.

Robustness Through View Stabilization

Proteus is designed with operational resilience in mind, and a key component of this is its View Stabilization process. This mechanism actively addresses the challenges posed by dynamic shifts in leadership or potential compromises within the distributed system. When a leader node fails or becomes unavailable, or if malicious activity is detected, View Stabilization swiftly identifies the change and adjusts the system’s understanding of its current state – its ‘view’ – without interrupting ongoing operations. By reliably reconciling differing perspectives across the network, this process prevents data inconsistencies and ensures that all nodes maintain a unified and accurate record, thereby safeguarding the integrity of the system even under adverse conditions. This proactive approach is fundamental to Proteus’s ability to provide consistent and dependable service in unpredictable environments.

The Proteus system maintains data consistency through a robust View Stabilization process designed to address inevitable divergences in its distributed view. When system components encounter differing information – creating ‘branches’ in the overall understanding – this process actively identifies these discrepancies and reconciles them. It doesn’t simply select a single ‘correct’ view, but instead merges information from multiple sources, ensuring that all components converge on a consistent state. This reconciliation isn’t a passive operation; the system continuously monitors for branching and proactively resolves inconsistencies before they escalate into data corruption or system failures, guaranteeing the integrity of stored information even amidst dynamic operational conditions and potential adversarial interference.

Maintaining a unified agreement, or consensus, within a distributed system like Proteus presents significant challenges when faced with constant change and potential malicious activity. View Stabilization addresses this by ensuring all participating nodes consistently interpret the system’s state, even as leadership shifts or individual components fail. This process doesn’t merely detect discrepancies; it actively reconciles them, preventing divergent understandings of data and transaction order. In dynamic environments where nodes join and leave frequently, and within potentially adversarial contexts where malicious actors might attempt to disrupt agreement, View Stabilization becomes paramount – a foundational mechanism for guaranteeing the system’s continued reliability and the integrity of its operations.

Ongoing research endeavors are dedicated to refining the efficiency and scalability of these view stabilization techniques. Current efforts concentrate on algorithmic optimizations to minimize overhead and enhance performance in high-throughput, low-latency scenarios. Beyond the initial implementation, investigations are underway to assess the adaptability of this approach to diverse distributed systems, including those operating in mobile, edge computing, and blockchain environments. The ultimate goal is to establish a broadly applicable framework for maintaining robust consensus and data integrity across a spectrum of challenging computational landscapes, potentially unlocking advancements in areas reliant on dependable distributed operation.

The design of Proteus, as detailed in the article, emphasizes a holistic approach to system integrity. It isn’t simply about patching vulnerabilities, but about architecting a ledger that anticipates and accommodates potential failures within Trusted Execution Environments. This resonates deeply with Kernighan’s observation that “Simplicity is prerequisite for reliability.” Proteus achieves this through a layered protocol-a CFT commit nested within a BFT audit-which, while seemingly complex, is born from a desire to distill the essential elements of both crash and Byzantine fault tolerance. The system’s strength lies not in adding features, but in refining the fundamental structure to ensure robust, auditable data integrity, even when facing compromised TEEs. This reflects a clear prioritization of essential functionality over superfluous complexity.

What’s Next?

The architecture presented by Proteus highlights a fundamental trade-off: the cost of absolute integrity versus practical performance. Embedding a Byzantine Fault Tolerance (BFT) audit within a Crash Fault Tolerance (CFT) commit protocol is an elegant reduction, yet it merely shifts the problem. The efficiency gained by leveraging CFT does not eliminate the overhead of the audit; it distributes it. Future work must address whether this distribution is, in fact, sufficient to justify the added complexity, or if the system is simply optimizing for a less visible bottleneck. The true cost, as always, lies in dependencies – here, the reliance on a correctly functioning audit mechanism, even within compromised Trusted Execution Environments (TEEs).

Current investigations focus heavily on TEE-specific attacks, but a more holistic view suggests that the real fragility lies in the boundaries between TEEs and the broader system. Proteus offers stronger guarantees within the TEE, but does little to address the potential for manipulation of input or output. A truly resilient system will require a rethinking of the entire trust boundary, not just fortifying a single component. Furthermore, the current design assumes a relatively static set of validators; scalability will demand a mechanism for dynamic membership and reputation management – a notoriously difficult problem.

Ultimately, the field must acknowledge that perfect security is an illusion. The goal is not to eliminate risk, but to manage it. Proteus represents a step toward a more nuanced approach, recognizing that different failure modes require different levels of protection. The path forward lies not in ever more complex protocols, but in simpler architectures that expose their limitations and allow for graceful degradation. Good architecture, after all, is invisible until it breaks.

Original article: https://arxiv.org/pdf/2602.05346.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/