Payment options on the (SF) frontier

[thrash]

Consider a science fiction setting with Traveller-ish technology -- specifically, no FTL comms other than ships themselves.

The setting is the very early days of interstellar exploration. Earth is not unified. Between the Outer Space Treaty and a bad "alien plague" scare early on, space-faring nations have largely decided to pass on formal colonization in favor of enforcing quarantine procedures and keeping an eye on each other. The gap is being filled by non-state agencies, mostly second-tier corporations with resources to invest but no other potentially high-growth options. The UN facilitates by selling licenses to develop (parts of) worlds, much like the International Seabed Authority does with deep sea mining.

At this point, operations are too thin on the ground to support an organized "sneaker net" of ships carrying data among the various licensed worlds. In particular, almost all traffic travels directly from the outposts to Earth (or rather, Earth's designated quarantine gateway system). There is very little travel across the frontier.

There are, however, freelance specialists who offer various services to the corporate colonies. Some of these are the usual camp followers -- food, drink, and entertainment -- but there are also private security contractors, professional services (engineers, etc.), and independent merchants and explorers. Many of these do travel from one colony to the next along the frontier in search of work.

How do these folks get paid, and pay for what they need?

Direct trade or barter can deal with many situations, of course, but has the same limitations it ever has. Hard currency is always an option, I suppose, but in the THS-lite home system I imagine this has fallen out of favor. One could substitute company scrip, but this has the very real danger of tying the independents to one corporation's holdings. There is also the problem of ultratech 3D printers and counterfeiting. Letters of credit are a traditional response, although they also suffer from the authentication problem.

Are there cryptologic solutions that might work well enough to discourage widespread or economically viable counterfeiting, yet still allow (mostly) anonymous transfers of purchasing power? Using Ultratech as an example, I can imagine a tiny, compact, printed computer the size and shape of a dollar bill, running some kind of self-authentication program with a large (~ GB) crypto key.

I'm opening the floor to suggestions. What do you think? What other possibilities are there?