Quote from: Matthew N. Wright on May 09, 2013, 10:40:39 PM

Quote from: babin on May 09, 2013, 10:29:01 PM

I don't say that there no need of blockchain

. Question is why there is need of transaction chain for every coin i.e. why balances information is not enough.

Where does the balance information come from? Surely it would come from calculating all the transactions.

Yes, but probably it is possible to decrease disk space/clients work-time if accumulate all transactions before the last checkpoint in one number per address - balance at the moment of last checkpoint.

Quote from: snail on May 09, 2013, 10:41:47 PM

You need the transaction history to make sure that someone hasn't spent the same bitcoins twice. If you store balance information, you still need the transaction history to verify that the balances are correct.

Quote from: TheRobot on May 09, 2013, 10:43:12 PM

Transaction chain shows proof of which address owns which coins, and tracking them back to their initial mining proves they are real coins. Without this transaction chain it would be considerably easier to make illegitimate coins.

If we store balances before the checkpoint and transactions only after checkpoint it seems to be as safe as the current bitcoin implementation (beacuse balance at the time of the checkpoint won't change even in the case of some forks). The double spents could be easily verified - it only need to check that the sum of transaction inputs less then the balance.