The MAA mainly contains three sections.
- The Prelude: The 'Prelude' is a calculation made with the keys (J and K) alone and it generates six numbers X0, Y0, V0, W, S and T which are used in the subsequent calculations. The keys are entered by the users. The generated numbers differ according to the keys entered and remain unchanged until a new key is installed.
- The Main Loop: In this section, two variables X and Y are initialized to X0 and Y0 variables from the Prelude. These values change according to the key (in the Prelude) and each message block entered (in the Main Loop). A calculation is made on each message block Mi of the message in the Main Loop employing X and Y; therefore for long messages it dominates the calculation. In the end, the authenticator value is calculated by using these variables, X and Y.
- The Coda
It consists of two operations of the Main Loop on two numbers S and T. In addition to the message blocks entered, two numbers S and T are also processed internally to finally produce the value of Z, the authenticator. S and T are generated according to the keys selected (J and K) in the Prelude section.
Mn+1 = S
Mn+2 = T
Finally the authenticator is calculated as Z= XOR(X,Y)
