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Basic File Template

This template checks for a pattern in provided files. 
id: ssh-public-key

info:
  name: SSH Public Key Detect
  author: pd-team
  severity: low

file:
  - extensions:
      - pub
    max-size: 1024 # read very small chunks

    matchers:
      - type: word
        words:
          - "ssh-rsa"

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Extension Denylist with No-Recursive

The below template is same as last one, but it makes use of an extension denylist along with the no-recursive option. 
id: ssh-private-key

info:
  name: SSH Private Key Detect
  author: pd-team
  severity: high

file:
  - extensions:
      - all
    denylist:
      - pub
    no-recursive: true
    max-size: 1024 # read very small chunks

    matchers:
      - type: word
        words:
          - "BEGIN OPENSSH PRIVATE KEY"
          - "BEGIN PRIVATE KEY"
          - "BEGIN RSA PRIVATE KEY"
          - "BEGIN DSA PRIVATE KEY"
          - "BEGIN EC PRIVATE KEY"
          - "BEGIN PGP PRIVATE KEY BLOCK"
          - "ssh-rsa"