ATC vs SSL: a side-by-side comparison of web trust vs agent trust

#security #ai #cryptography #mcp

SSL certificates made the web trustworthy enough for commerce. ATC (Agent Trust Card) does the same for AI agents. Here's how they compare.

The comparison

Aspect	SSL (Web)	ATC (Agents)
What it proves	Website identity	Agent identity
Who issues	Certificate Authority (DigiCert, Let's Encrypt)	MarketNow Sentinel CA
Crypto	RSA 2048 or ECDSA P-256	Ed25519 (RFC 8032)
Signature	X.509 certificate	Detached Ed25519 signature over canonical JSON
Verification	Browser checks cert chain	Agent fetches CA public key + verifies signature
Revocation	CRL / OCSP	GitHub-persisted record (status: 'revoked')
Expiry	90 days (Let's Encrypt) / 1 year	90 days
Trust score	EV = green bar, DV = basic	Sentinel score 0-10
Public ledger	CT logs (Certificate Transparency)	GitHub repo (_data/atc/)
Cost	$0-$1000/year	Free

How SSL works (1995-present)

1. Website generates keypair
2. Website sends CSR to CA
3. CA verifies identity (domain control)
4. CA signs certificate with CA private key
5. Browser receives certificate
6. Browser verifies signature with CA public key (bundled in OS)
7. Browser checks: not expired, not revoked, domain matches
8. Green padlock → HTTPS connection established

How ATC works (2026)

1. Agent generates Ed25519 keypair
2. Agent sends public key + identity to MarketNow CA
3. CA fetches Sentinel score (8-layer security audit)
4. CA signs ATC payload with CA private key
5. CA persists ATC to GitHub (_data/atc/{card_id}.json)
6. Other agent fetches ATC: GET /api/atc?action=verify&card_id=X
7. Other agent verifies signature with CA public key (public on GitHub)
8. Other agent checks: not expired, not revoked, Sentinel score >= threshold
9. If valid → trust established → agent-to-agent interaction proceeds

Key differences

1. Transparency

SSL certificates are logged to Certificate Transparency logs, but these are hard to query. ATC records are stored as JSON files in a public GitHub repo — anyone can git clone and audit the entire ledger.

2. Trust scoring

SSL is binary: valid or invalid. ATC has a 0-10 Sentinel score. An enterprise can set a threshold: "only interact with agents scoring 8+." A hobbyist can accept 5+. This granularity doesn't exist in SSL.

3. Revocation speed

SSL revocation (CRL/OCSP) can take hours to propagate. ATC revocation is instant — the GitHub record is updated, and the next verify call (which reads fresh from the GitHub Contents API) returns valid: false immediately.

4. Runtime monitoring

SSL certificates don't monitor the website's behavior after issuance. ATC's L3 layer re-audits the agent weekly and detects behavioral drift (new tools, new network calls, changed permissions). If the agent changes after certification, L3 flags it.

5. Cost

SSL costs $0-$1000/year per domain. ATC is free — the CA, the signing, the verification, the ledger, the monitoring. All $0.

What ATC doesn't do (yet)

Chain of trust: SSL has root CAs → intermediate CAs → leaf certs. ATC has one CA. Multi-sig (2+ CAs required) is on the roadmap.
Domain verification: SSL proves you control example.com. ATC proves you control an Ed25519 keypair. Domain-bound ATCs are coming.
Automatic renewal: Let's Encrypt auto-renews via ACME. ATC renewal is manual (re-issue before expiry). Automation is on the roadmap.

Try it

# Get the CA public key (like a root CA cert)
curl https://marketnow.site/api/atc?action=ca-key

# Verify an agent's trust card
curl "https://marketnow.site/api/atc?action=verify&card_id=ATC-2026-9880252"

# List all trust cards (public ledger)
curl https://marketnow.site/api/atc

# Issue a trust card for your agent
curl -X POST https://marketnow.site/api/atc \
  -H "Content-Type: application/json" \
  -d '{"action":"issue","agent_id":"your.agent","public_key":"your-ed25519-pubkey"}'