It could be that some validators of a token don’t report one way or the other about a transaction. This may happen because the validators have “netsplit” from one another and are unavailable, or because they are maliciously trying to freeze the sender’s token. In any event, the sender can attempt recover from this in a timely manner.
Intercoin’s ledger technology requires the sender to endorse a transaction after a supermajority of validators have approved it. Only then is it posted to the ledger. This allows the sender whose transaction is stuck to issue another transaction to another set of validators, and endorse whichever one is approved first, ignoring the others. This works because in crypto-currency, the sender ultimately has the say of whether to send the money or not.
Although it is extremely unlikely, in the event that the watchers of a token all collude to forget a transaction, either temporarily or permanently. To prevent this, we have several measures:
All tokens and transactions are encrypted, so validators do not know which tokens or accounts they are doing consensus for. All they have to store is the hash of the latest state of an encrypted token. Recipients are given the keys to decrypt the token and verify the latest owner.
Validators periodically check one another with “proof of resource” techniques. The key here is that these requests are anonymous (done by onion routing) and thus anyone who has the key (the other validators, the owner of the token, etc.) can verify that the validator still remembers the latest hash for the token. The anonymity means that a validator can’t keep up a lie, telling different parties about different forks. Thus, the validator either says the same thing all the time to everyone, or it is kicked out of the consensus.
Remembering the latest hash for a token is quite cheap in terms of memory resources, and tokens can eventually be retired, so Intercoin validation is quite efficient in terms of memory and CPU, far more than proof-of-work mining for Monero etc. It can even be implemented on personal computers running commercial software, but we must be careful to make it opt-in.
Intercoin Technology: Recovery