🔏 HMAC

Compute an HMAC with any hash.

Hash Output

Key Key encoding

Message Message encoding

Expected MAC (optional)

How it works

HMAC(K, m) = H((K′ ⊕ opad) ‖ H((K′ ⊕ ipad) ‖ m)), where K′ is the key padded to the hash’s block size (or hashed first if longer). Anyone with the key can create or check the MAC, so it proves integrity and authenticity between parties who share the key — not who signed it.