  Recently emerging Decentralized Finance (DeFi) takes the promise of
cryptocurrencies a step further, leveraging their decentralized networks to
transform traditional financial products into trustless and transparent
protocols that run without intermediaries. However, these protocols often
require critical external information, like currency or commodity exchange
rates, and in this respect they rely on special oracle nodes. In this paper, we
present the first study of DeFi oracles deployed in practice. First, we
investigate designs of mainstream DeFi platforms that rely on data from
oracles. We find that these designs, surprisingly, position oracles as trusted
parties with no or low accountability. Then, we present results of large-scale
measurements of deployed oracles. We find and report that prices reported by
oracles regularly deviate from current exchange rates, oracles are not free
from operational issues, and their reports include anomalies. Finally, we
compare the oracle designs and propose potential improvements.

Cryptography and Security