# HMAC-BLAKE2b-512 Base64 Signing

> HMAC-BLAKE2b-512 Base64 Signing is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-02).

Computes an HMAC using the BLAKE2b-512 hash function with a caller-supplied key and returns the result encoded as base64

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/hmac-blake2b512-base64?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/hmac-blake2b-512-base64-signing-7ee44944
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_vUmYHvNQ6d2yEeAAWL3Wx

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 hmac-blake2b-512-base64-signing-7ee44944 -d '<json body>'
```

Example prompt: Compute an HMAC-BLAKE2b-512 of the text 'Hello, world!' using the key 'my-secret-key' and give me the result as base64.

## When to prefer this

Use this endpoint when you specifically need BLAKE2b-512 as the underlying hash function for an HMAC operation — preferred over SHA-256 HMAC when higher performance or longer digest length is required. Choose this when the consuming system expects BLAKE2b-512 signatures specifically. For free or sandbox testing, prefer the unpaid POST /v1/sandbox/hmac-blake2b512-base64 endpoint first.

## Known failure modes

- Empty or missing key returns a validation error
- Text exceeds 100,000 character limit returns a payload-too-large error
- Missing required fields (key or text) returns a 400 bad request
- Network or service unavailability returns a 5xx error
- Payment failure (insufficient USDC balance) blocks the request via x402 protocol

## How this service works

Call when an agent needs an HMAC-blake2b512 of text with a caller-supplied key, encoded as base64. Exact $0.01 USDC. Prefer unpaid POST /v1/sandbox/hmac-blake2b512-base64 first.

## Output

Returns a base64-encoded HMAC-BLAKE2b-512 digest computed over the provided text using the supplied key. The output is a fixed-length base64 string representing the 512-bit MAC.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "key": {
   "type": "string",
   "examples": [
    "secret"
   ],
   "maxLength": 512,
   "minLength": 1,
   "description": "HMAC secret. Required on HMAC SKUs. Omit it for plain digests and checksums. The key is not stored."
  },
  "text": {
   "type": "string",
   "examples": [
    "hello"
   ],
   "maxLength": 100000,
   "minLength": 1,
   "description": "Message to digest. For raw-hex SKUs this is hex bytes; for utf16 or latin1 SKUs it is decoded with that encoding. Otherwise it is UTF-8 text."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/hmac-blake2b-512-base64-signing-7ee44944/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)