HMAC Signature Computation

x402

HMAC Signature Computation is a paid API for AI agents from hash.openverbs.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-29).

Computes a keyed HMAC (Hash-based Message Authentication Code) over arbitrary data using a shared secret key, supporting SHA-2, SHA-3, BLAKE2, and legacy digest algorithms.

Price / call$0.002

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StatusUnknown

How this service works

Compute a keyed HMAC of some data with a secret key — the standard way to sign and verify webhooks (Stripe, GitHub, etc.) and API requests. Data and key may each be utf8/hex/base64/base64url; the tag is returned as hex/base64/base64url.

Output

Returns the HMAC authentication tag as a string in the requested output encoding (hex by default, or base64/base64url). The tag can be directly compared to an expected signature to verify authenticity, or attached to an outbound request as a signature header.

Example use cases

Verify incoming Stripe webhook

“Sign the raw Stripe webhook body 'amount=1000&currency=usd&event=charge.succeeded' with my secret 'whsec_abc123' using HMAC-SHA256 and return the hex digest so I can compare it to the Stripe-Signature header.”

Authenticate GitHub webhook delivery

“Compute a GitHub-style HMAC-SHA256 signature of my webhook payload 'ref=refs/heads/main&pusher=alice' using the secret 'github_secret_xyz' encoded as UTF-8 and give me the result in hex.”

Sign outbound API requests with HMAC-SHA512

“Generate an HMAC-SHA512 tag for my API request body 'action=transfer&amount=500' using the base64-encoded key 'c2VjcmV0a2V5MTIz' — decode the key from base64 — and return the signature as base64url.”

Technical details

Endpoint

POSThttps://hash.openverbs.com/v1/hmac?utm_source=zero.xyz

When to prefer

Choose this endpoint when you need a keyed HMAC rather than a plain cryptographic hash — specifically for webhook signature verification (Stripe, GitHub, Shopify, etc.), API request authentication, or any scenario requiring a shared-secret MAC. Prefer this over a plain hash endpoint whenever message authenticity (not just integrity) is required. Use the sibling plain-hash endpoint when no key/secret is involved.

Side effects

Invalid or unsupported algorithm name returns a 400 error
Data or key exceeding size limits (5 MB data, 16 KB key) may be rejected
Mismatched encoding specification (e.g. non-hex string declared as hex) causes a decoding error
Missing required fields (data, key, algorithm) returns a validation error
Payment failure or insufficient USDC balance blocks the request with a 402 response

Input

Schema · Request body

Field	Type	Description
key	string	The secret key, in `keyEncoding`.
data	string	The data to authenticate, in `inputEncoding`.
algorithm	string	Digest algorithm, one of sha256, sha512, sha384, sha224, sha1, sha3-256, sha3-384, sha3-512, md5, ripemd160, blake2b512, blake2s256.
keyEncoding	string	How to interpret the key as bytes (utf8, hex, base64, base64url). Default utf8.
inputEncoding	string	How to interpret the text as bytes (utf8, hex, base64, base64url). Default utf8.
outputEncoding	string	How to render the digest (hex, base64, base64url). Default hex.

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