I am studying the concept of Electronic Cash, and in several reference I found that the criteria describing the ideal electronic cash system are as follows:
- Independence: The security of electronic cash cannot depend on any physical condition. Then the cash can be transferred through networks.
- Security: The ability to copy (reuse) and forge the cash must be prevented.
- Privacy (Untraceability): The privacy of the user should be protected. That is, the relationship between the user and his purchases must be untraceable by anyone.
- Off-line payment: When a user pay the electronic cash to a shop, the procedure between the user and the shop should be executed in an off-line manner. That is, the shop does not need to be linked to the host in user’s payment procedure.
- Transferability: The cash can be transfered to other users.
- Dividability: One issued piece of cash worth value C (dollars) can be subdivided into many pieces such that each subdivided piece is worth any desired value less than C and the total value of all pieces is equivalent to C.
Now, what of the above properties are achieved by the Bitcoin system? I guess 1, 2 and 5 are trivially achieved, and I think 3 and 6 are not fully achieved. I wonder if 4 is achieved, and I'm particularly interested in this off-line property.