[{"type":"report","id":"BLC-STUDY-0139","title":"Hashcash: A Denial of Service Counter-Measure","author":[{"literal":"Adam Back"}],"issued":{"date-parts":[[2002]]},"publisher":"Adam Back","URL":"http://www.hashcash.org/papers/hashcash.pdf","note":"Rights status: Official external source only. Not a licence to republish the paper."}]