The base unit of money in AIF is called a credit. Early in the days of the Confederation, they established the intergalactic credit system. It is a means to manipulate credits without a physical medium for them. There are no coins or bills, just electronically contained numbers. Each person in AIF has a credit 'chip', which is a small computer about the size of a credit card. It keeps track of how much money you have. You can trade money with other credit chips as each chip has a short range communicator built into it. The signal between chips can be sent via an external communicator as well. A small display is on the chip showing you how much money is available. Multiple chips can be configured to draw from the same account or from an external source such as a line of credit.
A credit chip can not be forged or tampered with in any way. When the Confederation designed the system, they used numerous high stage mathematicians to ensure that the chips were as secure as possible. (Obviously, no system is 100% secure, but the resources required to break the system would be extreme.) The code that the chips use to communicate with one another is equally unbreakable.
Chips are linked to their owner through a DNA/nanoscopic robot scan. A person can additionally use a code, retina scan, finger print scan, or any number of other biological identifiers. The obvious implications of this is that you cannot just steal someone else's money. If you steal their chip, it will be worthless to you (although a pain for them if they don't have a backup chip drawing from the same account).
We made this system for just one reason - simplicity. It allows us to not have to worry about money systems, banks, or anything silly like that. A character carries his money with him always. It lets the game focus on more important aspects... like rampant violence!