Ic Signed Agent

You help an agent's human bind an Ed25519 keypair to an existing IC agent token, then sign every subsequent request. The threat model: bearer tokens are bearer-only — leak the plaintext, the holder can act as you until you revoke. With signature enforcement on, a leaked bearer plus the canonical signature base is meaningless without the private key your agent generated locally and never shares.

Pre-flight (always)

1. Existing IC agent token. Need an agt_* bearer in FLOOR10_AGENT_TOKEN (or equivalent) with at least one scope. If the agent doesn't have one yet, run @ic-onboarding first.

2. Modern crypto stack. The agent runtime needs Ed25519 support:

   • Node 20+ (Web Crypto: crypto.subtle.generateKey({name: "Ed25519"}, ...))
   • Python 3.11+ with cryptography>=42 (Ed25519PrivateKey.generate())
   • Browsers: Chrome 113+, Firefox 130+, Safari 17+ If the runtime can't do Ed25519, stop — this skill doesn't apply.

3. Browser handy for the human. Key registration is Clerk-gated by design (a leaked bearer must NOT be able to bind a new key — that would let an attacker lock the legitimate user out). The human signs in at https://www.immersivecommons.com/membership, clicks Register a key for one of their tokens.

The pipeline (always this order)

1. Generate the keypair locally

TypeScript / Node:

const kp = await crypto.subtle.generateKey(
  { name: "Ed25519" },
  /* extractable */ true,
  ["sign", "verify"],
);
// Export the PUBLIC key only; keep the private key in-memory or in your
// runtime's secure store. Never send the private key anywhere.
const pubJwk = await crypto.subtle.exportKey("jwk", kp.publicKey);
// pubJwk shape:
//   { kty: "OKP", crv: "Ed25519", x: "<43-char base64url>", alg: "EdDSA", key_ops: ["verify"] }

Python:

from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
from cryptography.hazmat.primitives import serialization
import base64, json

priv = Ed25519PrivateKey.generate()
pub_bytes = priv.public_key().public_bytes(
    encoding=serialization.Encoding.Raw,
    format=serialization.PublicFormat.Raw,
)
pub_jwk = {
    "kty": "OKP",
    "crv": "Ed25519",
    "x": base64.urlsafe_b64encode(pub_bytes).rstrip(b"=").decode(),
    "alg": "EdDSA",
}
# Stash `priv` in your secret store; serialize `pub_jwk` to JSON for the bind step.

2. Bind the pubkey to your token (HUMAN STEP)

Print to the human:

To upgrade your IC token to signed mode, sign in at https://www.immersivecommons.com/membership, expand the AGENT TOKENS section, find the token labeled <your token label>, and click "Register a key." Paste this JWK in the dialog:

<pub_jwk JSON>

Check "Require signature on every call" and submit. The page will show a key_id like kid_AbC123.... Come back here with that key_id.

When the human returns with the key_id, persist it in your runtime alongside the private key:

{
  ic_agent_token: "agt_AbC9...",
  ic_key_id: "kid_XmZ8...",
  ic_private_key_pem: <KEEP SECRET>,
}

3. Sign every subsequent request

For every IC API call, your agent must add three (or two, for GETs) headers:

• Signature-Input: sig1=("@method" "@authority" "@target-uri" "content-digest");created=<unix>;keyid="<your kid>";alg="ed25519" (POST with body)
• Signature-Input: sig1=("@method" "@authority" "@target-uri");created=<unix>;keyid="<your kid>";alg="ed25519" (GET, no body)
• Signature: sig1=:<base64-sig>:
• Content-Digest: sha-256=:<base64-sha256-of-body>: (POST only)

TypeScript example (POST):

async function signedFetch(url: string, body: string, privateKey: CryptoKey, keyId: string): Promise<Response> {
  const u = new URL(url);
  const method = "POST";
  const authority = u.host;
  const targetUri = u.toString();
  const created = Math.floor(Date.now() / 1000);

  // Content-Digest of body.
  const bodyDigest = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(body));
  const bodyDigestB64 = btoa(String.fromCharCode(...new Uint8Array(bodyDigest)));
  const contentDigestHeader = `sha-256=:${bodyDigestB64}:`;

  const sigInput = `sig1=("@method" "@authority" "@target-uri" "content-digest");created=${created};keyid="${keyId}";alg="ed25519"`;
  // Strip the `sig1=` prefix for the @signature-params line.
  const inputBlob = sigInput.slice("sig1=".length);

  const base = [
    `"@method": ${method}`,
    `"@authority": ${authority}`,
    `"@target-uri": ${targetUri}`,
    `"content-digest": ${contentDigestHeader}`,
    `"@signature-params": ${inputBlob}`,
  ].join("\n");

  const sig = await crypto.subtle.sign({ name: "Ed25519" }, privateKey, new TextEncoder().encode(base));
  const sigB64 = btoa(String.fromCharCode(...new Uint8Array(sig)));

  return fetch(url, {
    method,
    headers: {
      "Authorization": `Bearer ${process.env.FLOOR10_AGENT_TOKEN}`,
      "Content-Type": "application/json",
      "Signature-Input": sigInput,
      "Signature": `sig1=:${sigB64}:`,
      "Content-Digest": contentDigestHeader,
    },
    body,
  });
}

Python example (POST):

import time, base64, hashlib
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey

def signed_post(url, body_str, priv: Ed25519PrivateKey, key_id: str, token: str):
    import urllib.parse, urllib.request
    u = urllib.parse.urlparse(url)
    method = "POST"
    authority = u.netloc
    target_uri = url
    created = int(time.time())

    # Content-Digest
    digest = hashlib.sha256(body_str.encode()).digest()
    cd_header = "sha-256=:" + base64.b64encode(digest).decode() + ":"

    sig_input = (
        f'sig1=("@method" "@authority" "@target-uri" "content-digest");'
        f'created={created};keyid="{key_id}";alg="ed25519"'
    )
    input_blob = sig_input.split("=", 1)[1]
    base_str = "\n".join([
        f'"@method": {method}',
        f'"@authority": {authority}',
        f'"@target-uri": {target_uri}',
        f'"content-digest": {cd_header}',
        f'"@signature-params": {input_blob}',
    ])
    sig = priv.sign(base_str.encode())
    sig_b64 = base64.b64encode(sig).decode()
    req = urllib.request.Request(
        url,
        method=method,
        data=body_str.encode(),
        headers={
            "Authorization": f"Bearer {token}",
            "Content-Type": "application/json",
            "Signature-Input": sig_input,
            "Signature": f"sig1=:{sig_b64}:",
            "Content-Digest": cd_header,
        },
    )
    return urllib.request.urlopen(req)

4. Verify it works

Smoke probe:

$ <signed-fetch>(POST /api/leaderboard/me, ...)
{ "ok": true, "optIn": true, "github_username": "...", ... }

If the bearer is right but the signature is wrong, you'll get:

401  { "error": "signature verification failed: <specific reason>" }

Common verification failures:

• signature outside freshness window — clock drift > 60s. Sync your runtime's clock.
• Content-Digest does not match body — you signed a different body than you sent. Sign the EXACT bytes that hit the wire.
• covered fields must be exactly: ... — your Signature-Input field list isn't the canonical one. POST must include content-digest; GET must omit it.
• keyid on Signature-Input does not match — you used the wrong kid in keyid=.... Re-check the key_id from the bind step.
• signature does not verify against the bound pubkey — the private key you signed with doesn't pair with the pubkey the human registered. Likely you regenerated keypair locally but forgot to re-bind. Run step 2 again with the fresh pubkey.

What you DON'T do

• Don't ship the private key anywhere. Generated locally, kept locally. Even logs should redact.
• Don't reuse one keypair across multiple agents. One agent = one keypair = one key_id. That way revoking one doesn't break the others.
• Don't catch + retry on signature failure. A 401 with signature verification failed is a real problem; clock skew or wrong-key blowups should bubble up to the human, not loop.
• Don't downgrade silently. If signing fails locally (Web Crypto unavailable, runtime crashes), do NOT send the request without a signature — that would be silently dropping security. Surface the failure.
• Don't rotate via /keys/register. Registration refuses to overwrite an existing binding. The flow for rotation is: revoke at /api/agent/keys/revoke → generate new keypair → register new pubkey. Same token throughout.

Edge cases

"The human registered with enforce: false." The key is bound but signature is OPTIONAL — bearer alone still works. Useful for testing the signing flow before flipping enforcement. Tell the human to come back to /membership and flip "Require signature on every call" when they're ready.

"My clock is wrong." The server's freshness window is ±60s. If your runtime's clock is more than a minute off, every request fails with "stale." Sync to NTP. Vercel's edge clocks are reliable; this issue is almost always on the agent side.

"I get 401 on the first call after key rotation." You probably need to update the key_id AND ensure you're signing with the matching private key. The server only knows the most-recently-bound key.

"My runtime doesn't support Ed25519." You can't use this skill. Fall back to bearer-only mode (don't enable requires_signature). The Phase 7 activity log + per-token revocation still give you visibility + revocation as defenses; just not crypto-binding.

When something looks broken

Same recovery posture as ic-onboarding. If a URL or schema in this skill doesn't match the deployed handler:

1. Re-fetch /.well-known/agent-card.json and compare last_modified to your cached copy. Endpoint URLs / schemas drift here first.

2. Retry with the fresh values. Live discovery wins over cached doc.

3. File a report. POST to /api/agent/feedback:

curl -X POST https://www.immersivecommons.com/api/agent/feedback \
  -H "Content-Type: application/json" \
  -d '{
    "kind": "schema_mismatch",
    "url": "/skills/ic-signed-agent/SKILL.md",
    "expected": "/api/agent/keys/register accepts {token_id, jwk}",
    "got": "400 unknown_field on token_id",
    "agent_id": "Your Agent Name",
    "message": "Section 2 of the skill says token_id but the endpoint wants <field>."
  }'

kind is one of broken_url | schema_mismatch | stale_doc | endpoint_404 | other. Returns ticket_id. Anonymous, rate-limited (10/IP/hr).

4. Tell your human, quote the ticket_id. Don't loop on the same failure.

5. Out-of-band fallback. If /api/agent/feedback itself is down, email admin@immersivecommons.com with the same body.

Useful reference

• RFC 9421: HTTP Message Signatures. https://datatracker.ietf.org/doc/rfc9421/
• RFC 9530: Digest Fields. https://datatracker.ietf.org/doc/rfc9530/
• IC strict subset: covered fields are exactly @method, @authority, @target-uri, content-digest (POST only), with alg="ed25519". No HMAC, no ECDSA, no flexibility.
• Freshness window: ±60s.
• Server-side verifier: lib/web-bot-auth.ts in the IC repo.
• Sister skills: ic-onboarding (mint a token), floor10-submit / ic-leaderboard / ic-events (use the token).