ANSI X9.9 MAC
The Financial Institution (Wholesale) Message Authentication Standard (ANSI X9.9-1986) defines a process for the authentication of messages from originator to recipient, and this process is called the Message Authentication Code (MAC) calculation method.
The ANSI X9.9 standard defines five options. The MAC Generate and MAC Verify verbs implement option 1, binary data.
Figure 1 shows the MAC calculation for binary data. In this figure, KEY is a 64-bit key, and T1 - Tn are 64-bit data blocks of text. If Tn is less than 64 bits long, binary zeros are appended to the right of Tn. Data blocks T1…Tn are DES CBC-encrypted with all output discarded except for the final output block, On.