Abstract
The essence of blockchain smart contracts lies in the execution of business logic code in a decentralized architecture in which the execution outcomes are trusted and agreed upon by all the executing nodes. Despite the decentralized and trustless architectures of the blockchain systems, smart contracts on their own cannot access data from the external world. Instead, smart contracts interact with off-chain external data sources, called oracles, whose primary job is to collect and provide data feeds and input to smart contracts. However, there is always risk of oracles providing corrupt, malicious, or inaccurate data. In this paper, we analyze and present the notion of trust in the oracles used in blockchain ecosystems. We analyze and compare trust-enabling features of the leading blockchain oracle approaches, techniques, and platforms. Moreover, we discuss open research challenges that should be addressed to ensure secure and trustworthy blockchain oracles.
Highlights
Bitcoin was the first cryptocurrency that eliminated third party by introducing a new decentralized computational architecture in the financial sector
COMPARISON OF EXISTING SOLUTIONS Based on the extensive review, we found that existing blockchain oracle solutions can be differentiated based on different aspects as detailed in Table 1 and Table 2
Provable is an example of a centralized oracle service leveraging a variety of authenticity proofs such as TLSNotary Proof; whereas, TownCrier is another centralized solution that is based on Trusted Execution Environments (TEEs), where it uses Intel’s Software Guard Extensions (SGX) (Software Guard eXtensions) to ensure that responses from HTTPS queries can be verified as authentic
Summary
Bitcoin was the first cryptocurrency that eliminated third party by introducing a new decentralized computational architecture in the financial sector. Considering the essential need of trustworthy oracles for the future blockchain applications, different proposals, early implementations, and platforms have emerged recently [15]–[18]. Researchers studied the notion of trust and proposed a framework to perform the reliability analysis of different blockchain oracle platforms [19]. H. Al-Breiki et al.: Trustworthy Blockchain Oracles: Review, Comparison, and Open Research Challenges smart contracts and oracles. We articulate a concise taxonomic discussion on blockchain oracles that employ centralized and decentralized trust models and design patterns to enable inbound and outbound interactions between smart contracts and various types of oracles. We conduct an exhaustive search and present a detailed review and comparison of state-of-the-art blockchain oracle platforms and early implementations/proposals.
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