The Request MAC Key sequence allows the merchant to request a new key for computing MAC values. Required inputs are the merchant id, the merchant passphrase and the value of the current MAC Key against which to issue a renewal. Merchants can request a renewal at any time such as when an employee with access to the current key terminates their employment with the merchant. Because the information used in order transactions is very structured and highly predictable, it is expected that MAC keys will naturally expire within a predefined time interval. At most, keys should expire from one year of their issue. A better practice would have them expire at least every six months. Merchants generating a high volume of traffic might benefit from the security of having keys expire every three months.

When a new key is requested, the request is matched against the known merchant values of merchant id, passphrase and current key value. If this authentication is successful, then a new cryptographically strong randomly generated key is issued to the merchant over a secure web connection. This key is a four byte key with a specified sequential serial number. Upon request, the key is returned to the merchant over the secure web connection as a hexadecimal value and simultaneously stored within the merchant configuration database.