Sign a message
key = secret-key-123message = Hello, world!
Result: Enter a key and message, then click Sign to see the HMAC signature.
HMAC-SHA512 Generator
Compute an HMAC-SHA512 (Hash-based Message Authentication Code) using a secret key and a message. HMAC provides message authentication - it verifies that a message hasn't been tampered with AND was created by someone holding the key. Unlike digital signatures, HMAC does not provide non-repudiation (both parties share the same key). Everything runs in your browser.
Privacy: this tool processes your data entirely in your browser. Nothing you paste or type is sent to the server.
Enter your values and press Calculate — the result appears here.
Worked examples
Frequently asked questions
What is HMAC?
HMAC (Hash-based Message Authentication Code) combines a cryptographic hash function with a secret key to produce a signature. It verifies both the integrity (the message hasn't changed) and authenticity (it was created by someone with the key) of a message.
HMAC vs digital signatures - what's the difference?
HMAC uses a shared secret key - both parties can create and verify the signature. Digital signatures use asymmetric keys (private key signs, public key verifies), providing non-repudiation. Use HMAC when both parties are trusted; use digital signatures when you need to prove who created the message.
Is my key or message sent to a server?
No. HMAC computation happens entirely in your browser using the Web Crypto API. Nothing is transmitted anywhere.
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