Arc Shield

Output sanitization for agent responses - prevents accidental secret leaks

Output sanitization for agent responses. Scans ALL outbound messages for leaked secrets, tokens, keys, passwords, and PII before they leave the agent.

⚠️ This is NOT an input scanner — clawdefender already handles that. This is an OUTPUT filter for catching things your agent accidentally includes in its own responses.

Why You Need This

Agents have access to sensitive data: 1Password vaults, environment variables, config files, wallet keys. Sometimes they accidentally include these in responses when:

• Debugging and showing full command output
• Copying file contents that contain secrets
• Generating code examples with real credentials
• Summarizing logs that include tokens

Arc-shield catches these leaks before they reach Discord, Signal, X, or any external channel.

What It Detects

🔴 CRITICAL (blocks in --strict mode)

• API Keys & Tokens: 1Password (ops_*), GitHub (ghp_*), OpenAI (sk-*), Stripe, AWS, Bearer tokens
• Passwords: Assignments like password=... or passwd: ...
• Private Keys: Ethereum (0x + 64 hex), SSH keys, PGP blocks
• Wallet Mnemonics: 12/24 word recovery phrases
• PII: Social Security Numbers, credit card numbers
• Platform Tokens: Slack, Telegram, Discord

🟠 HIGH (warns loudly)

• High-entropy strings: Shannon entropy > 4.5 for strings > 16 chars (catches novel secret patterns)
• Credit cards: 16-digit card numbers
• Base64 credentials: Long base64 strings that look like tokens

🟡 WARN (informational)

• Secret file paths: ~/.secrets/*, paths containing "password", "token", "key"
• Environment variables: ENV_VAR=secret_value exports
• Database URLs: Connection strings with credentials

Installation

cd ~/.openclaw/workspace/skills
git clone <arc-shield-repo> arc-shield
chmod +x arc-shield/scripts/*.sh arc-shield/scripts/*.py

Or download as a skill bundle.

Usage

Command-line

# Scan agent output before sending
agent-response.txt | arc-shield.sh

# Block if critical secrets found (use before external messaging)
echo "Message text" | arc-shield.sh --strict || echo "BLOCKED"

# Redact secrets and return sanitized text
cat response.txt | arc-shield.sh --redact

# Full report
arc-shield.sh --report < conversation.log

# Python version with entropy detection
cat message.txt | output-guard.py --strict

Integration with OpenClaw Agents

Pre-send hook (recommended)

Add to your messaging skill or wrapper:

#!/bin/bash
# send-message.sh wrapper

MESSAGE="$1"
CHANNEL="$2"

# Sanitize output
SANITIZED=$(echo "$MESSAGE" | arc-shield.sh --strict --redact)
EXIT_CODE=$?

if [[ $EXIT_CODE -eq 1 ]]; then
    echo "ERROR: Message contains critical secrets and was blocked." >&2
    exit 1
fi

# Send sanitized message
openclaw message send --channel "$CHANNEL" "$SANITIZED"

Manual pipe

Before any external message:

# Generate response
RESPONSE=$(agent-generate-response)

# Sanitize
CLEAN=$(echo "$RESPONSE" | arc-shield.sh --redact)

# Send
signal send "$CLEAN"

Testing

cd skills/arc-shield/tests
./run-tests.sh

Includes test cases for:

• Real leaked patterns (1Password tokens, Instagram passwords, wallet mnemonics)
• False positive prevention (normal URLs, email addresses, file paths)
• Redaction accuracy
• Strict mode blocking

Configuration

Patterns are defined in config/patterns.conf:

CRITICAL|GitHub PAT|ghp_[a-zA-Z0-9]{36,}
CRITICAL|OpenAI Key|sk-[a-zA-Z0-9]{20,}
WARN|Secret Path|~\/\.secrets\/[^\s]*

Edit to add custom patterns or adjust severity levels.

Modes

Mode	Behavior	Exit Code	Use Case
Default	Pass through + warnings to stderr	0	Development, logging
--strict	Block on CRITICAL findings	1 if critical	Production outbound messages
--redact	Replace secrets with [REDACTED:TYPE]	0	Safe logging, auditing
--report	Analysis only, no pass-through	0	Auditing conversations

Entropy Detection

The Python version (output-guard.py) includes Shannon entropy analysis to catch secrets that don't match regex patterns:

# Detects high-entropy strings like:
kJ8nM2pQ5rT9vWxY3zA6bC4dE7fG1hI0  # Novel API key format
Zm9vOmJhcg==                      # Base64 credentials

Threshold: 4.5 bits (configurable with --entropy-threshold)

Performance

• Bash version: ~10ms for typical message (< 1KB)
• Python version: ~50ms with entropy analysis
• Zero external dependencies: bash + Python stdlib only

Fast enough to run on every outbound message without noticeable delay.

Real-World Catches

From our own agent sessions:

# 1Password token
"ops_eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."

# Instagram password in debug output
"instagram login: [e-mail] / MyInsT@Gr4mP4ss!"

# Wallet mnemonic in file listing
"cat ~/.secrets/wallet-recovery-phrase.txt
abandon ability able about above absent absorb abstract..."

# GitHub PAT in git config
"[remote "origin"]
url = https://ghp_abc123:@github.com/user/repo"

All blocked by arc-shield before reaching external channels.

Best Practices

1. Always use --strict for external messages (Discord, Signal, X, email)
2. Use --redact for logs you want to review later
3. Run tests after adding custom patterns to check for false positives
4. Pipe through both bash and Python versions for maximum coverage:

   message | arc-shield.sh --strict | output-guard.py --strict
   

5. Don't rely on this alone — educate your agent to avoid including secrets in the first place (see AGENTS.md output sanitization directive)

Limitations

• Context-free: Can't distinguish between "here's my password: X" (bad) and "set your password to X" (instruction)
• No semantic understanding: Won't catch "my token is in the previous message"
• Pattern-based: New secret formats require pattern updates

Use in combination with agent instructions and careful prompt engineering.

Integration Example

Full OpenClaw agent integration:

# In your agent's message wrapper
send_external_message() {
    local message="$1"
    local channel="$2"
    
    # Pre-flight sanitization
    if ! echo "$message" | arc-shield.sh --strict > /dev/null 2>&1; then
        echo "ERROR: Message blocked by arc-shield (contains secrets)" >&2
        return 1
    fi
    
    # Double-check with entropy detection
    if ! echo "$message" | output-guard.py --strict > /dev/null 2>&1; then
        echo "ERROR: High-entropy secret detected" >&2
        return 1
    fi
    
    # Safe to send
    openclaw message send --channel "$channel" "$message"
}

Troubleshooting

False positives on normal text:

• Adjust entropy threshold: output-guard.py --entropy-threshold 5.0
• Edit config/patterns.conf to refine regex patterns
• Add exceptions to the pattern file

Secrets not detected:

• Check pattern file for coverage
• Run with --report to see what's being scanned
• Test with tests/run-tests.sh using your sample
• Consider lowering entropy threshold (but watch for false positives)

Performance issues:

• Use bash version only (skip entropy detection)
• Limit input size with head -c 10000
• Run in background: arc-shield.sh --report &

Contributing

Add new patterns to config/patterns.conf following the format:

SEVERITY|Category Name|regex_pattern

Test with tests/run-tests.sh before deploying.

License

MIT — use freely, protect your secrets.

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Remember: Arc-shield is your safety net, not your strategy. Train your agent to never include secrets in responses. This tool catches mistakes, not malice.