Sentinel Protocol is a Security Intelligence Platform for Blockchain (SIPB) to protect valuable crypto assets against hacking, scams and frauds. Its decentralized Threat Reputation Database (TRDB) is provided on public blockchain for crypto exchanges, payments and wallet services so that the value of stolen currencies can be incapacitated. Sentinel Protocol operates based on collective intelligence of cybersecurity specialists, as well as preventive security measures such as machine learning for behavior modeling and cost-effective distributed sandboxing.