What is a message authentication code?

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A Message Authentication Code (MAC) is a small block of data attached to a message that the recipient uses to verify the integrity of the message. One can think of this as similar to the wax seals that used to be placed on letters and formal correspondence to verify the sender’s identity and confirm that the message had not been opened. These codes are used when sending certain types of encrypted or protected data so that the sender can verify that the message has not been compromised. Message authentication codes may appear in messages such as electronic fund transfers and emails.

When a message is generated, the MAC is created at the same time. The message is sent to the recipient, and when the recipient opens it, the content of the message is run through an algorithm to create a new message authentication code. This new code is compared to the code sent along with the original message. If the codes match, the message will be authenticated. If there is a difference, it indicates that something has changed between the sender and recipient of the message.

The MAC generation and comparison process usually happens behind the scenes. The sender and receiver depend on the encryption programs they use to handle MACs. The program that generates the message authentication code is written by a programmer familiar with encryption needs. Custom applications can be written for high security situations, or people can use generic programs that are readily available.

Several different methods can be used to create a MAC, including a stream cipher, hash function, or block cipher. Also known as checksum, MAC can be one of several layers of security designed to keep prying eyes away from messages and ensure that messages are not tampered with or altered without alerting the recipient. When a recipient opens a message that has been compromised, an alert is displayed to inform the user that the message’s authentication code does not match and that there is a problem with the message.

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Encryption is a constantly evolving process. As new techniques are developed, new methods to break them are also created. People interested in data security should think several steps ahead to figure out decryption methods so that they can build strong security systems. The development of supercomputers aided this process, allowing cryptographers to develop and experiment with highly advanced encryption methods.

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