# ENTROPY.RIP Notary Sign

> ENTROPY.RIP Notary Sign is a paid API for AI agents from entropy.rip, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).

Cryptographically signs a hash with metadata and returns a PGP signature as a timestamped proof of existence

## Facts

- Endpoint: POST https://entropy.rip/api/notary/sign
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/entropy-rip-notary-sign-35dc7a07
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_L_I6V8VfeeFDuYSiOrGm3

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability entropy-rip-notary-sign-35dc7a07 -d '<json body>'
```

Example prompt: Can you notarize this SHA-256 hash — e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 — with the metadata 'contract-draft-v2 2024-06-10' and give me back a PGP-signed proof of existence?

## When to prefer this

Use this endpoint when you need a lightweight, low-cost ($0.02 USDC) cryptographic proof-of-existence for a hash — especially in autonomous agent workflows, audit trails, or timestamping scenarios where a PGP-signed attestation suffices. Prefer this over blockchain-based notarization when cost and latency matter more than on-chain immutability.

## Known failure modes

- Missing or malformed hash field returns a 400 error
- Invalid or non-hex hash string may be rejected
- Payment not included or insufficient USDC triggers a 402 response
- Server-side signing key unavailable causes a 500 error
- Metadata field exceeding length limits may be rejected

## How this service works

A suite of survival tools for autonomous AI agents. Residential proxies, dead man's switches, ephemeral storage, and cryptographic proofs of existence.

## Output

A JSON object containing a PGP-armored signature (-----BEGIN PGP SIGNATURE...) that cryptographically attests the submitted hash and metadata were received and signed at a specific point in time, usable as a proof-of-existence record.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "hash": {
   "type": "string",
   "description": "Content hash"
  },
  "metadata": {
   "type": "string",
   "description": "metadata"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "signature": "-----BEGIN PGP SIGNATURE..."
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/entropy-rip-notary-sign-35dc7a07/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from entropy.rip](https://www.zero.xyz/host/entropy.rip/llms.txt)