A virtual currency can be designed by issuing coins with unique ids connected to owners with cryptographic signatures. The coins are transferred between owners in this way:

1. The current owner A unlocks a coin with a private key.
2. A signs the coin with the new owner B's public key.
3. A registers the coin in a distributed hash table.
4. A sends a message to B about the coin having been transferred.
5. B checks the distributed hash table to verify ownership.

Coins of different values 1, 10, 100, 1000 and so on can be issued to make it practical. So for example if a person X wants to send 235 coins to person Y, then two 100, three 10 and five 1 coins are sent in the transaction.