Keyed-Hash Message Authentication Code (HMAC) is a security mechanism used to verify the integrity and authenticity of messages. It combines a cryptographic hash function with a secret key. This ensures that only someone with the key can generate a valid HMAC, making it hard for unauthorized users to forge messages.In practice, when two parties want to communicate securely, the sender creates an HMAC by hashing the message along with the secret key. The recipient can then recreate the HMAC using the same key and the received message. If the HMACs match, it confirms that the message has not been altered and is indeed from the sender.HMAC is crucial for securing transactions and data in decentralized systems, preventing tampering and ensuring that the information comes from a trusted source. Its use helps maintain trust and security among participants in a network, safeguarding against various attacks.