Explore a groundbreaking conference talk on redactable blockchain technology in permissionless settings, presented at the 2019 IEEE Symposium on Security & Privacy. Delve into the challenges posed by immutable blockchains, particularly Bitcoin, and their potential to store harmful or illegal data. Discover an innovative solution that allows for efficient data redaction without compromising the blockchain's integrity or relying on heavy cryptographic tools. Learn about the consensus-based voting system, policy-driven redaction process, and the protocol's ability to offer public verifiability and accountability. Examine the formal security definitions, proofs, and a proof-of-concept implementation demonstrating the protocol's minimal overhead compared to immutable blockchains. Gain insights into the potential impact of this technology on law enforcement agencies and the future of blockchain systems.