Town Crier

Abstract

Smart contracts are programs that execute autonomously on blockchains. Their key envisioned uses (e.g. financial instruments) require them to consume data from outside the blockchain (e.g. stock quotes). Trustworthy data feeds that support a broad range of data requests will thus be critical to smart contract ecosystems. We present an authenticated data feed system called Town Crier (TC). TC acts as a bridge between smart contracts and existing web sites, which are already commonly trusted for non-blockchain applications. It combines a blockchain front end with a trusted hardware back end to scrape HTTPSenabled websites and serve source-authenticated data to relying smart contracts. TC also supports confidentiality. It enables private data requests with encrypted parameters. Additionally, in a generalization that executes smart-contract logic within TC, the system permits secure use of user credentials to scrape access-controlled online data sources. We describe TC's design principles and architecture and report on an implementation that uses Intel's recently introduced Software Guard Extensions (SGX) to furnish data to the Ethereum smart contract system. We formally model TC and define and prove its basic security properties in the Universal Composibility (UC) framework. Our results include definitions and techniques of general interest relating to resource consumption (Ethereum's "gas" fee system) and TCB minimization. We also report on experiments with three example applications. We plan to launch TC soon as an online public service.

A survey on the security of blockchain systems

“…Even if the Relay module is attacked, or the network communication packets are tampered, it will not change the normal function of TC. TC system provides a robust security model for the smart contracts' off-chain data interaction, and it has already been launched online as a public service [71].…”

TLS-N: Non-repudiation over TLS Enabling Ubiquitous Content Signing

“…Any other contract can use such blockchain-based information. This disintermediation removes the need for an additional third party acting as an oracle [46], [26]. Further use cases are (iii) Web Archives [2], [38] for web content or deleted social media content [14], and (iv) proving misbehaviour in P2P networks [34], [16].…”

“…3) Other existing solutions: There are other solutions providing similar properties, such as TLSnotary [42] and Town Crier [46] that we will discuss in Section VI-C. While TLSnotary only works for older TLS versions and requires trust in a third party, Town Crier is a specific solution for smart contracts that requires a third party with special hardware and trust in the attestation service.…”

“…In the following, we describe orthogonal solutions that offer evidence of TLS sessions using a trusted third party, e.g., TLSnotary [42] and Town Crier [46].…”

“…2) Town Crier: Town Crier [46] allows disintermediation through the Intel SGX technology. Town Crier can provide publicly verifiable data feeds based on the contents of a TLS session, but it can also do more as it has computational resources and allows further confidentiality.…”