These are identified by adding the hash name, eg HMAC-MD5, HMAC-SHA1 etc. The ] does something similar to this, but not exactly the same. HMACĪ defence against the weakness of the simple algorithm is to append a secret key at the start and end of the message when calculating the MAC. It is like signing an important letter and then allowing a total stranger to add any extra data they like to it after you posted it, so that their additions appear to come from you. This is a fairly limited attack, but still serious in some cases. However, the attacker can add blocks to the end of the message, and recalculate the new MAC incrementally. To validate the data, repeat the MAC calculation, and ensure that the MAC values match.Īn attacker cannot alter the message without detection, because he does not know the key and so cannot recalculate the MAC value. Of course, the message which is stored or transmitted must NOT have the secret key still prepended. The advantage of MAC algorithms is that they are very very fast and can usually be easily offloaded to the hardware. They take a message and a secret shared key and provide an output that can be authenticated by the other party to the key. It is then possible to store or transmit the original message and the MAC together. Message Authentication Code (MAC) algorithms are a sort of keyed hash. To calculate the MAC, concatenate the key and the message, and takes the hash value of the concatenated data. The algorithm uses a secret a key (which can be any sequence of bytes of any length you wish).
We can illustrate this using a simple (though unfortunately not secure) algorithm.
It is possible to use any hash algorithm as the basis of a MAC. Here are some of the most common MAC algorithms. Tags cryptography message authentication code mac hmac
0 kommentar(er)
