Anyway .. what about the proof-of-work and the impossibility of double spending with blocks every 20 seconds?
Who gives me an explanation?
Some notes on your double-spend/51% worries:
1. The only thing that's possible is that a person with 51% can un-spend their own transactions. So that limits them to money in their wallet.
2. That is only possible if they can generate more blocks than the rest of the network.
3. Having 51% of the blocks only increases probability, and does not introduce any new certainty. It's possible to double spend even if you only have 1% of the network but got really lucky and generated more blocks than the network.
4. It's more profitable to mine digitalcoin with 51% of power than it is to try and destroy it. In fact, there would be no reason for someone to attempt such a thing, and if they did, it's very unlikely to succeed.
5. Transactions require an exchange of private keys between two parties. So really the only way to double spend is to control a whole sub-network or broadcast transactions to all network. In your subnetwork, not even one computer is allowed to be outside your control. The problem is, as soon as any outside client connects to your sub-network, they will have consensus data from other peers and re-download the whole blockchain.
So you can see how difficult that concept is to apply. Also, I am considering an update to the system where nodes that detect bad blocks communicate it directly with the rest of the network just to add an additional layer of security.
