HMAC Generator

Generate HMAC signatures.

Secret Key:

Algorithm:

Message:

HMAC Signature:

HMAC signature will appear here...

About HMAC Generator

The HMAC Signature Generator is a specialized cryptographic utility designed to compute Hash-based Message Authentication Codes (HMAC) compliant with RFC 2104 and FIPS PUB 198. By combining a shared secret cryptographic key with a message payload through an underlying hash function (SHA-256, SHA-512, or MD5), HMAC guarantees both data integrity and authenticity. It is essential for signing REST API requests (e.g., AWS Signature Version 4, Stripe webhooks, GitHub webhooks) and verifying message authenticity.

Key features

Standard Algorithm Selection: Supports HMAC-SHA256, HMAC-SHA512, and HMAC-MD5 with exact cryptographic adherence
Client-Side Key Isolation: Shared secret keys and private messages are processed strictly in browser memory, never sent over the network
Real-Time Live Calculation: Automatically recalculates signatures immediately upon modifying either the key, message, or algorithm
Hexadecimal Digest Formatting: Produces standardized lowercase hexadecimal signature strings ready for HTTP header authorization

How to use

Enter Secret Key: Input your shared secret key or API signing secret into the designated key field.
Select Algorithm & Input Message: Choose HMAC-SHA256, SHA-512, or MD5, and paste your JSON payload or request string.
Copy Generated HMAC Signature: Review the resulting hexadecimal HMAC signature and click "Copy" to use in your API headers.

FAQ

What is an HMAC and how does it differ from a regular hash?

A standard hash (like SHA-256) only verifies data integrity. An HMAC incorporates a secret cryptographic key, ensuring both data integrity and proof that the message originated from a party holding the secret key.

Is my secret key safe when using this tool?

Yes, completely. All cryptographic operations are executed locally in your browser using client-side JavaScript. Your secret key and message payload are never transmitted to any external server.

Which HMAC algorithm should I choose for modern webhooks?

HMAC-SHA256 is the industry standard for modern webhooks (used by GitHub, Stripe, Shopify, and Slack) offering high performance and robust security.

Can HMAC signatures prevent replay attacks?

HMAC itself verifies message authenticity. To prevent replay attacks, webhooks commonly include a timestamp in the signed payload and verify it against a short validity window.

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About HMAC Generator

Key features

Standard Algorithm Selection: Supports HMAC-SHA256, HMAC-SHA512, and HMAC-MD5 with exact cryptographic adherence

Client-Side Key Isolation: Shared secret keys and private messages are processed strictly in browser memory, never sent over the network

Real-Time Live Calculation: Automatically recalculates signatures immediately upon modifying either the key, message, or algorithm

Hexadecimal Digest Formatting: Produces standardized lowercase hexadecimal signature strings ready for HTTP header authorization