TCP/IP Tutorial and Technical Overview - IBM Redbooks

5. Capture
Up to this point, no money has changed hands. The capture request from the
merchant tells the acquirer to transfer the previously authorized amount to its
account.
In fact, capture can be incorporated as part of the authorization
request/response (see the previous information). However, there are
situations in which the merchant might want to capture the funds later. For
example, most mail order operations do not debit the credit card account until
the goods have been shipped.
There are several other transactions within the SET specification, but the
previous summary shows the principles on which it is based.
22.15.3 The SET certificate scheme
The SET specification envisions hundreds of thousands of participants
worldwide. Potentially, each of these would have at least one public key
certificate. In fact, the protocol calls for an entity to have multiple certificates in
some cases. For example, the acquirer payment gateways need one for signing
messages and another for encryption purposes.
Chapter 22. TCP/IP security 883