The primary function of credsticks is similar to that of turn-of-the-millennium debit cards. They provide access to an account in some bank somewhere, and let you make electronic fund transfers from that account to other accounts over the financial network.
They're somewhat smarter than debit cards, though, in that they can do direct stick-to-stick transfers without involving the financial network at the time of the transaction. These transactions do have to be registered with the network later, in order for the funds to actually be transferred from the payer's account to the payee's; stick-to-stick transfers just let you postpone the network portion of the transaction as a convenience measure if a credstick reader connected to the network isn't immediately available.
Stick-to-stick transfers involve an exchange of temporary encryption keys that allow the credsticks involved to validate the transaction the next time they next access the network. The transaction doesn't actually occur until both credsticks involved have validated it, so it's possible to stiff someone on a payment after the fact simply by not ever using the stick again. This renders the stick useless, but given a throwaway account, can be done effectively. Letting your Johnson pay you with a stick-to-stick transfer is probably a bad idea.
Regular credsticks access an account that's connected to an identity, with an associated SIN, and the stick can also be used to identify oneself as the person who holds that SIN. The SIN can be either a real one or a false one. In the latter case, credstick readers may identify it as false when transactions are made, with results ranging from indifference to getting shot to death by security, depending on the circumstances. Real or false, the user has to confirm their identity in one of several ways, depending on the transaction limit on the stick.
|Type||Transaction Limit||Required ID|
Note that this means that there's a limit to how false false identities can actually be. In order for a user to identify correctly to use the credstick, the credstick has to have information that actually matches the user's on file with the bank. This isn't a particular problem with standard sticks that merely require the user to know the correct passcode, but the higher-limit sticks require increasing amounts of the user's actual personal information to be on file, ranging from fingerprints at the low end to full cellular scans for the unlimited ebony credsticks. Having that information in the database can mean that if forensics finds fingerprints or skin flakes or other evidence (voiceprints and retinal scans are more difficult, but not impossible, to leave behind) at the scene of a crime, they can search the database and link that information to a SIN or SINs and flag those for attention when they're next used. Whether the name associated with the SIN is the one the user's parents gave them is pretty much irrelevant at that point.
Certified credsticks differ from regular ones in that the bank account they draw from is not associated with any particular identity. Mere possession of the credstick grants access to the account, and the stick can simply be handed off to another person. This has obvious advantages for shadowrunners, and they will probably want to do most of their business with certified sticks. They can't be used for identification, however, because they aren't associated with any identity.
Despite the lack of identity associated with certified credsticks, it's still possible to follow transactions through them and flag sticks associated with known criminal transactions for attention, so money laundering is still a useful occupation. It's more difficult with certified cred than with regular credsticks, though, and the lack of actual identity data associated with the account reduces the number of ways the account can become associated with criminal activity.
While lines of credit are still available in the 2060s, they're available only to people with real SINs or very high quality fake ones. Even shadowrunners that can meet the requirements to get them are unlikely to find them useful in the shadows. Shadow transactions tend to be unfriendly to credit, at least the sort of credit that doesn't involve large men with the middle name "the" coming by to break your kneecaps if you miss your payments.