Message Authentication Code

• A message authentication code (MAC) is a short piece of information used to authenticate a message.
  • A MAC algorithm accepts as input a secret key and a message to be authenticated.
  • It outputs a MAC, which is sometimes called a tag.

• The MAC value protects both a message's integrity as well as its authenticity by allowing verifiers, who also possess the secret key, to detect any changes to the message content.

• A message authentication code is different than a digital signature.
  • MAC values are both generated and verified using the same secret key.
    • Sender and receiver of a message must agree on keys before initiating communications.
      • As is the case with private key encryption.
  • A message authentication code does not provide the property of non-repudiation offered by digital signature.

What is a digital certificate?

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© 2006 John Michael Pierobon

Notes