Protect MCP Setup

# 1. Install the plugin (adds hooks + skill to your project)
claude plugin install wshobson/agents/protect-mcp

# 2. Create ./protect.cedar (see below). The plugin installs the hooks.

# 3. Create the signing key once (protect-mcp 0.7.4 sign does not create it).
#    An existing key is never replaced. See references/receipt-format.md to rotate.
if [ ! -e ./protect-mcp.key ]; then
  d=$(mktemp -d) && npx [email protected] init --dir "$d" && mv "$d/keys/gateway.json" ./protect-mcp.key
fi
chmod 600 ./protect-mcp.key
echo "/protect-mcp.key" >> .gitignore

# 4. Use Claude Code normally. Every tool call is now policy-evaluated
#    and produces a signed receipt in ./receipts/

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": ".*",
        "hooks": [
          { "type": "command", "command": "\"${CLAUDE_PLUGIN_ROOT}\"/hooks/evaluate.sh" }
        ]
      }
    ],
    "PostToolUse": [
      {
        "matcher": ".*",
        "hooks": [
          { "type": "command", "command": "\"${CLAUDE_PLUGIN_ROOT}\"/hooks/sign.sh" }
        ]
      }
    ]
  }
}

// Read-only tools: one rule can name several tools in `when`. Add WebFetch
// with your own URL rule.
permit (principal, action == Action::"MCP::Tool::call", resource) when {
    resource == Tool::"Read" || resource == Tool::"Glob" || resource == Tool::"Grep"
};

// Safe commands only; git limited to read subcommands
permit (principal, action == Action::"MCP::Tool::call", resource == Tool::"Bash") when {
    context has input && context.input has command &&
    (context.input.command like "git status*" || context.input.command like "git diff*" ||
     context.input.command like "git log*" || context.input.command like "git show*" ||
     context.input.command like "npm*" || context.input.command like "ls*" ||
     context.input.command like "cat*" || context.input.command like "echo*" ||
     context.input.command like "pwd*" || context.input.command like "test*")
};

// No chaining (`&` also denies `2>&1`), `$` expansion, redirection (`>` or
// `<`, which covers `<(`), file output (`git diff --output`), or rm -rf
forbid (principal, action == Action::"MCP::Tool::call", resource == Tool::"Bash") when {
    context has input && context.input has command &&
    (context.input.command like "*;*" || context.input.command like "*&*" ||
     context.input.command like "*|*" || context.input.command like "*$*" ||
     context.input.command like "*`*" || context.input.command like "*>*" ||
     context.input.command like "*<*" || context.input.command like "*\n*" ||
     context.input.command like "*--output*" || context.input.command like "*rm -rf*")
};

// Writes only inside the project (paths are absolute), never via `..`
permit (principal, action == Action::"MCP::Tool::call", resource) when {
    (resource == Tool::"Write" || resource == Tool::"Edit") &&
    context has input && context.input has file_path &&
    context.input.file_path like "/path/to/project/*"
};
forbid (principal, action == Action::"MCP::Tool::call", resource) when {
    (resource == Tool::"Write" || resource == Tool::"Edit") &&
    context has input && context.input has file_path &&
    (context.input.file_path like "*/../*" || context.input.file_path like "*/..")
};

PUB=$(node -p 'JSON.parse(require("fs").readFileSync("./protect-mcp.key")).publicKey')
npx @veritasacta/[email protected] --replay-chain ./receipts/receipts.jsonl --key "$PUB"
# Exit 0 = every receipt verified
# Exit 1 = a receipt failed (tampered, wrong key, or malformed line)
# Exit 2 = the file could not be read

/verify-receipt receipt.json
/audit-chain --last 20