What is HMAC Generator Online?
HMAC (Hash-based Message Authentication Code) combines a secret key with a hash function to produce a signature that proves both message integrity and authenticity. It is the standard mechanism used by AWS Signature V4, Stripe webhooks, GitHub webhooks, and most REST API authentication schemes. This hmac generator online tool allows you to quickly generate or verify signatures without revealing your secret keys to a remote server. Enter your message and secret key to compute the HMAC signature instantly using local browser cryptography. HMAC is critical because a standard hash can be vulnerable to length-extension attacks. By involving a secret key in two separate passes of the hash function, HMAC provides a robust authentication layer that ensures only holders of the secret key could have produced the signature for that specific payload.
How to Use HMAC Generator Online
- Paste your message or payload into the "Message" field.
- Enter your secret key in the "Secret" field.
- Select the hash algorithm (HMAC-SHA256 is most common).
- The HMAC signature is computed instantly. Copy it for use in your API request.
Example
HMAC-SHA256 signature
Input
Message: "order_id=123" | Key: "mysecret"Output
a4b5c6d7...Developer Tips
When verifying webhooks, always use a constant-time comparison function (e.g., `crypto.timingSafeEqual` in Node.js) to prevent timing attacks that could leak information about the signature.
Frequently Asked Questions
What is the difference between a hash and an HMAC?
A hash is deterministic — anyone can compute it. An HMAC requires a secret key, so only parties who possess the key can verify the signature.
How do I verify a Stripe webhook?
Compute HMAC-SHA256 of the raw request body using your Stripe webhook secret. Compare your result to the "Stripe-Signature" header value.