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Message Authentication Code (MAC)

Message Authentication Codes (MACs) are similar to hash values, but are computed using a session key. Because of this difference, you must possess the session key in order to recompute the hash value to verify that the base data has not changed.

The MACs implemented by the Microsoft RSA Base Provider are of the most common sort. That is, they are block cipher MACs. This method encrypts the base data with a block cipher and then uses the last encrypted block as the hash value. The encryption algorithm used to build the MAC is the one that was specified when the session key was created.

Warning The same session key should not be used for both message encryption and MAC generation. Doing so greatly increases the risk of your messages being decoded.

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