rules:
  - id: incorrect-use-of-blockhash
    message: blockhash(block.number) and blockhash(block.number + N) always returns 0.
    metadata:
      category: security
      technology:
        - solidity
      cwe: "CWE-341: Predictable from Observable State"
      confidence: HIGH
      likelihood: LOW
      impact: MEDIUM
      subcategory:
          - vuln
      references:
        - https://blog.positive.com/predicting-random-numbers-in-ethereum-smart-contracts-e5358c6b8620
    patterns:
      - pattern-either:
          - pattern: blockhash(block.number)
          - pattern: blockhash(block.number + $N)
          - pattern: blockhash(block.number * $N)
          - pattern: block.blockhash(block.number)
          - pattern: block.blockhash(block.number + $N)
          - pattern: block.blockhash(block.number * $N)
    severity: ERROR
    languages:
      - solidity