# Touchstone Verifiable Timestamp (Proof-of-Existence)

> Touchstone Verifiable Timestamp (Proof-of-Existence) is a paid API for AI agents from touchstone.locomot.io, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Binds a SHA-256 digest to a public drand randomness beacon round, producing a trustless anti-backdating receipt proving data existed no earlier than a specific instant.

## Facts

- Endpoint: GET https://touchstone.locomot.io/timestamp
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/touchstone-verifiable-timestamp-proof-of-existence-d669017e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_DyiVJ7G2aE6ijeXkr8Oj9

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 touchstone-verifiable-timestamp-proof-of-existence-d669017e
```

Example prompt: Create a trustless anti-backdating proof for this SHA-256 digest a3f1c2d4e5b6789012345678abcdef0123456789abcdef0123456789abcdef01 — stamp it to the current drand round so I have a verifiable receipt that this data existed right now.

## When to prefer this

Use this endpoint when you need a trustless, privacy-preserving proof that data existed at or before a specific moment in time, without relying on any centralized timestamp authority. Ideal for intellectual property protection, contract timestamping, audit trails, and freshness proofs where the input can be kept private as an opaque hash. Prefer over blockchain-based timestamping when low cost, speed, and privacy (no on-chain data) matter.

## Known failure modes

- Invalid or malformed SHA-256 hex digest (not 64 hex characters) returns an error
- Verify operation called without a round parameter fails with missing parameter error
- Provided round number does not exist yet or is in the future — beacon not yet available
- Both data and hash provided simultaneously may cause ambiguity or rejection
- Network unavailability of drand beacon causes service failure
- Round number integer out of valid range returns an error

## How this service works

Verifiable timestamp (trustless proof-of-existence / freshness proof): bind a hash to a drand round for an anti-backdating receipt — proves data existed no earlier than a public instant, with no trusted timestamp authority. Privacy: stamp an opaque sha256 digest.

## Output

A JSON receipt containing: the operation (stamp/verify), the SHA-256 digest, the drand round number, the UTC time of that round, a 'not_earlier_than' ISO timestamp, a cryptographic beacon proof object, a commitment string, the engine name, whether the result is deterministic given the round, and a human-readable claim string summarizing the proof.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "properties": {
      "op": {
       "enum": [
        "stamp",
        "verify"
       ],
       "type": "string",
       "description": "operation; default stamp"
      },
      "data": {
       "type": "string",
       "description": "text to stamp (sha256'd)"
      },
      "hash": {
       "type": "string",
       "description": "OR a 64-hex sha256 digest (private)"
      },
      "round": {
       "type": "integer",
       "description": "pin a drand round; verify requires it"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "properties": {
    "op": {
     "type": "string"
    },
    "claim": {
     "type": "string"
    },
    "proof": {
     "type": "object"
    },
    "round": {
     "type": "integer"
    },
    "beacon": {
     "type": "object"
    },
    "digest": {
     "type": "string"
    },
    "engine": {
     "type": "string"
    },
    "commitment": {
     "type": "string"
    },
    "digest_source": {
     "type": "string"
    },
    "round_time_utc": {
     "type": "string"
    },
    "not_earlier_than": {
     "type": "string"
    },
    "deterministic_given_round": {
     "type": "boolean"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/touchstone-verifiable-timestamp-proof-of-existence-d669017e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from touchstone.locomot.io](https://www.zero.xyz/host/touchstone.locomot.io/llms.txt)