security

Small keys.
Short expiries.
Boring cryptography.

about-us.md uses primitives that stopped being controversial fifteen years ago: ed25519 signatures, JWKS-shaped key discovery, short-lived scoped envelopes, and a public revocation ledger. No new maths. No custom hash functions. No secret-sharing dances. Just enough plumbing to make identity portable.

Key model

Root key. Ed25519. Held by the customer at username.md. Rotated by publishing a signed rotation to their /.well-known/keys.
Agent subkeys. Each delegated agent (Claude, ChatGPT, Operator, custom) gets its own scoped subkey signed by the root. Scope is enforced at verification, not just at delegation.
Business keys (this site). Issuer surfaces like about-us.md publish /.well-known/agent.json with their own ed25519 identity — the site is dogfooded.
No secret ever crosses the wire. Only public keys and signatures leave the signer.

Discovery

GET https://username.md/u/aclay/.well-known/keys { "keys": [ { "kid": "aclay-2026-06", "kty": "OKP", "crv": "Ed25519", "x": "…", "use": "sig", "expires": "2027-06-01T00:00:00Z" } ], "ttl": 60 }

Standard JWKS shape with a small extension: ttl is the cache guidance, and expires lets you reject even-if-cached keys past their retirement.

Revocation

Time-based. Every intent envelope has expires — usually minutes. A stolen envelope has a very short useful lifetime.
Key-based. Customer removes a compromised agent's subkey. Your JWKS cache expires within TTL, next verification fails.
Ledger-based (planned). A public append-only revocation ledger for hard incidents — signed "this kid is dead as of ts." Cachable globally, verifiable independently.

Replay defense

Nonce + expires. Store nonce for (now, expires + skew). Reject repeats.
Audience binding. Envelopes name their audience (your business handle). An envelope for competitor.com is not valid for you.
Scope minimization. Envelopes are per-intent. A refund-request envelope can't be replayed as an account-close.

Threat model — what we protect against

Threat	Legacy	about-us.md
Email spoof	Widely trusted	Signature over `from` — no valid envelope from a spoofed handle
SIM swap	SMS 2FA falls	Handle key survives — recovery re-proves ownership, not phone number
Password reuse	Credential stuffing	No password to reuse — signature or nothing
Rogue AI agent	Blocked or trusted, all-or-nothing	Only listed subkeys act; unknown agents fail verification
Replay of intercepted request	Often possible	Nonce + expires + audience — replay window is minutes and single-use

What we don't try to solve

Endpoint compromise. If the customer's laptop is popped, their key is popped. That's what expiries, subkeys, and revocation are for.
Legal identity. A handle isn't a passport. If your workflow needs government IDV, do that alongside — verified handles reduce friction, they don't replace regulated KYC.
Anti-abuse economics. Cheap handles = spam. We charge a small friction (or a signed proof-of-personhood) for handle creation. Design partners get input on the exact model.

Reporting

Found something? Email security@holdingco.com — signed envelopes appreciated but not required.

Small keys.Short expiries.Boring cryptography.