If MessageAuthenticationCode (MAC) is used, details are available from your certification analyst on how to implement this. Message Authentication Code (MAC) data is not required for contactless-only Interac transactions; it is required for all contact transactions unless Voltage encryption is used. The calculation for building the MAC String uses the POSSequenceNbr value.

Some responses indicate that the MAC value must be reset.

• MAC Verification on Transaction Response
• Resetting the MAC Value
• MacKey
• Key Exchange