During the installation you are prompted to specify a path to place the encryption key file DotshoppingcartMaster.key. This file is very important. It contains the key which is used to encrypt the sensitive data e.g. credit card# inside the database. The file itself is protected by DPAPI of Windows. So it's a good idea to create a backup of the file and save it offline. In case the machine crashes you can restore the DotshoppingcartMaster.key.

Here is the how you back up the DotShoppingCartMaster.key.