Authorization is a crucial security component of many distributed systems handling sensitive data or actions, including IoT systems. We present the design of a fully decentralized authorization system, WAVE, that operates at a global scale providing fine-grained permissions, non-interactive delegation and proofs of permission that can be efficiently verified, while still supporting revocation. Using smart contracts on a public blockchain, it allows rich and complex policies to be expressed and is resistant to DoS attacks without relying on any central trusted parties. We also present a novel mechanism for protecting the secrecy of resources on the public blockchain, without out-of-band channels or interaction between granters, provers or verifiers.

We implemented WAVE, which has now been running for over 500 days. We show that WAVE is efficient enough to support city-scale federation with millions of participants and permission policies.