From an NSA presentation on Stefan Brands work in the 90s. He devised an almost perfect cryptographic digital cash system that has all the anonymity and flexibility of cash with the caveat that people would have to be accountable to double spending via a traditional banking system.

https://groups.csail.mit.edu/mac/classes/6.805/articles/mone...

>the caveat that people would have to be accountable to double spending via a traditional banking system.

If the systems security is ultimately based on a reputation model then the system is just as secure as the existing banking system.

Which is fine, because the global banking system basically depends on double spending through loans (fractional reserve). If you double spend (spend more than you have), you accumulate a collectable debt and face legal consequences if you don't pay.

There's no way around this under Brands system, someone has to hold the keys to mint new currency, although it can be federated in the sense than every bank, store, or even person, could have their own issue.