Public transactions are, by and large, 'account based' -- the money is not in possession of those who claim credit for it, but rather filed under their name on some distant server
Safeguarding the servers where the money credits are documented
Verifying the identities of the traders who wish to exchange funds between cloud accounts
Securing the money transfer communications between the traders, and the respective servers.
The challenges here are:
The unique challenge is the verification of identities for which passwords are still the backbone. Increasingly any verification dialogue that is based on repeat identification data is considered insecure, and asymmetric cryptography is employed to practice non-repeat verification dialogues.
Public financial transactions are, by and large, based on payment card framework, which has dominated public payment for the past half a century. Payment cards emerged in the 60's, and successfully adapted themselves to the computer era, and then to the Internet era. Only recently has this framework been challenged with the emerging technology of digital money.