[Paper Review] PDFS: Practical Data Feed Service for Smart Contracts

Juan Guarnizo, Paweł Szałachowski|arXiv (Cornell University)|Aug 20, 2018

Blockchain Technology Applications and Security16 references3 citations

TL;DR

PDFS is a practical, application-layer data feed service that enables smart contracts to securely and efficiently consume authenticated, easily-parsable data from external sources without modifying TLS or relying on trusted third parties. By linking content providers directly to blockchain via a tamper-evident data structure monitored by a smart contract, PDFS ensures data authenticity, prevents equivocation and censorship, and enables new monetization models for content providers.

ABSTRACT

Smart contracts are a new paradigm that emerged with the rise of the blockchain technology. They allow untrusting parties to arrange agreements. These agreements are encoded as a programming language code and deployed on a blockchain platform, where all participants execute them and maintain their state. Smart contracts are promising since they are automated and decentralized, thus limiting the involvement of third trusted parties, and can contain monetary transfers. Due to these features, many people believe that smart contracts will revolutionize the way we think of distributed applications, information sharing, financial services, and infrastructures. To release the potential of smart contracts, it is necessary to connect the contracts with the outside world, such that they can understand and use information from other infrastructures. For instance, smart contracts would greatly benefit when they have access to web content. However, there are many challenges associated with realizing such a system, and despite the existence of many proposals, no solution is secure, provides easily-parsable data, introduces small overheads, and is easy to deploy. In this paper we propose PDFS, a practical system for data feeds that combines the advantages of the previous schemes and introduces new functionalities. PDFS extends content providers by including new features for data transparency and consistency validations. This combination provides multiple benefits like content which is easy to parse and efficient authenticity verification without breaking natural trust chains. PDFS keeps content providers auditable, mitigates their malicious activities (like data modification or censorship), and allows them to create a new business model. We show how PDFS is integrated with existing web services, report on a PDFS implementation and present results from conducted case studies and experiments.

Motivation & Objective

• To address the lack of secure, efficient, and easily-parsable data feeds for smart contracts that do not rely on trusted third parties or modify TLS protocols.
• To enable content providers to publish data with cryptographic authenticity while remaining auditable and incentivized through blockchain-based payments.
• To prevent malicious behavior such as data equivocation and censorship by content providers using a blockchain-monitored tamper-evident data structure.
• To allow smart contracts to verify data authenticity efficiently without expensive public-key operations or complex protocol changes.
• To support new business models where content providers are paid for data verification, increasing adoption and sustainability.

Proposed method

• PDFS extends content providers with a tamper-evident data structure (TDS) that binds data to a blockchain address, enabling verifiable and auditable data publication.
• The TDS is updated and monitored by a smart contract that ensures data consistency and prevents content providers from equivocating or altering past data.
• Data is published in a structured, machine-readable format (e.g., JSON) to enable easy parsing by smart contracts without additional processing.
• Authentication is achieved via cryptographic signing of data batches by the content provider, with proofs stored on the blockchain, enabling efficient verification by smart contracts.
• A blockchain-based API allows smart contracts to query content providers directly, mitigating censorship by enabling public access to data even if the provider attempts to block requests.
• Monetary incentives are natively supported via blockchain transactions, allowing content providers to charge for data verification and enabling sustainable data feed ecosystems.

Experimental results

Research questions

• RQ1 How can smart contracts securely consume external data feeds without relying on trusted third parties or modifying the TLS protocol?
• RQ2 Can a system be designed to provide both data authenticity and efficient, structured parsing for smart contracts without introducing new trust assumptions?
• RQ3 How can content providers be incentivized to publish authentic data while being prevented from equivocating or censoring queries?
• RQ4 What architectural approach enables practical deployment of authenticated data feeds at the application layer without requiring changes to transport-layer protocols?
• RQ5 Can a blockchain-monitored data structure effectively prevent data manipulation and ensure auditability without relying on trusted hardware or complex attestation mechanisms?

Key findings

• PDFS enables data authenticity and efficient verification for smart contracts without modifying the TLS stack or requiring trusted hardware, reducing deployment barriers.
• The system prevents content provider equivocation and censorship through a blockchain-monitored tamper-evident data structure (TDS), ensuring data consistency and auditability.
• Data is structured in a machine-readable format (e.g., JSON), enabling easy parsing by smart contracts without additional transformation or processing overhead.
• The solution supports native blockchain-based payments, allowing content providers to monetize data feeds and enabling new sustainable business models.
• PDFS requires only application-layer changes, making it deployable today without requiring protocol-level standardization or changes to existing TLS infrastructure.
• Compared to prior systems like TLS-N, Town Crier, or TLSNotary, PDFS avoids expensive verification operations and does not require trusted hardware or TLS stack modifications.