MACalgoritm

MAC algorithm, or message authentication code algorithm, is a class of cryptographic primitives used to verify both the integrity and the authenticity of a message in a symmetric-key setting. A MAC takes a secret key and a message as input and outputs a short tag. The same key and the same message will always produce the same tag, and a different key or message should produce a different tag with high probability. Verification is performed by recomputing the tag on the received message and comparing it to the transmitted tag.

A MAC provides confidentiality of the key and non-repudiation by the sender, but it does not offer non-repudiation in the sense of public-key signatures. The security goal is existential unforgeability under chosen-message attacks: an adversary who does not know the secret key should not be able to produce a valid tag for any new message. Good MAC designs resist key leakage, collision, and forgery attempts, and are designed to be efficient in software and hardware.

Common constructions include HMAC, which uses a cryptographic hash function with inner and outer pads; and CMAC, which uses a block cipher such as AES. Other MACs include Poly1305-based schemes. MACs are widely used in protocols and systems such as TLS, IPsec, SSH, and API authentication, often with standardized tag lengths that balance security and efficiency.

Key management is essential: keys must be generated securely, stored with restricted access, and rotated periodically to maintain security. MACs are not intended for non-repudiation and rely on secret keys kept only by trusted parties.