# FractalAI Post-Quantum x402 Signing Service

> FractalAI Post-Quantum x402 Signing Service is a paid API for AI agents from fractalai.net.co, paid per call via x402, $0.02/call, status down (last checked 2026-10-13).

Signs a hex digest using ML-DSA-65 (CRYSTALS-Dilithium / NIST FIPS 204) post-quantum cryptography and returns a verifiable base64 signature with public key via the x402 payment protocol.

## Facts

- Endpoint: POST https://fractalai.net.co/api/x402/sign?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: down
- Last checked: 2026-10-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fractalai-post-quantum-x402-signing-service-01c32231
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_zr02wTWVhR6zr2zji0ouW

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 fractalai-post-quantum-x402-signing-service-01c32231 -d '<json body>'
```

Example prompt: Sign this hex digest '9f86d081884c7d659a2feaa0c55ad015a3bf4f1b2b0b822cd15d6c15b0f00a08' using ML-DSA-65 post-quantum cryptography so I can verify the signature later.

## When to prefer this

Choose this endpoint when you need a post-quantum (quantum-computer-resistant) digital signature using the NIST FIPS 204 standard (ML-DSA-65 / CRYSTALS-Dilithium-3). Prefer it over classical ECDSA or RSA signing when future-proofing against quantum threats is a requirement, when compliance with NIST post-quantum standards is needed, or when integrating with the FractalAI blockchain ecosystem. The x402 micropayment model makes it suitable for per-use agent workflows at $0.02 per call.

## Known failure modes

- Invalid or malformed hex digest — returns error indicating bad input format
- Payment failure or insufficient USDC balance via x402 — returns 402 Payment Required
- Signature generation failure on the blockchain node side — returns 500 server error
- Malformed x402 payment header — returns 400 or 402 indicating payment protocol error

## How this service works

The first AI-native Layer 1 blockchain built from scratch in Rust. Post-quantum cryptography (CRYSTALS-Dilithium), Proof of Fractal Work consensus, WASM smart contracts, and 460+ RPC endpoints. Mine FRAC tokens with fractal analysis instead of hash puzzles.

## Output

Returns a JSON object containing: the algorithm name ('ml-dsa-65'), the original hex digest, a base64-encoded 3309-byte ML-DSA-65 signature (NIST FIPS 204 / Dilithium-3), a base64-encoded 1952-byte public key for offline verification, and optionally a payment settlement receipt with transaction details (scheme, network, asset, txHash, payer, settled status).

## 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",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object"
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST",
      "PUT",
      "PATCH"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "digest": "9f86…",
  "algorithm": "ml-dsa-65",
  "signature": "BASE64_ML_DSA65_3309B",
  "public_key": "BASE64_ML_DSA65_1952B"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fractalai-post-quantum-x402-signing-service-01c32231/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fractalai.net.co](https://www.zero.xyz/host/fractalai.net.co/llms.txt)