Authenticate a message
key = secretmessage = Hello
Result: HMAC proves the message was signed by the key holder.
HMAC Demonstrator
EDUCATIONAL DEMONSTRATION ONLY — HMAC (Hash-based Message Authentication Code) proves both the integrity and authenticity of a message. It combines a secret key with a hash function, ensuring that only someone with the key can produce or verify the HMAC.
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
Why not just hash the message?
A plain hash only proves integrity (no tampering). HMAC proves both integrity AND authenticity — only someone with the secret key could have produced it.
How does HMAC differ from digital signatures?
HMAC uses a shared secret (symmetric). Digital signatures use public/private key pairs (asymmetric). HMAC cannot prove which party created the message — only that both parties share the key.
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