Quote from: justusranvier on February 17, 2014, 11:40:29 PM

Quote from: tvbcof on February 17, 2014, 11:25:22 PM

What I still do not fully understand is whether capturing and manipulating the transaction ID of a transaction would result in neither the original nor the modification making it to confirmation due to the perception of a double-spend attack, or would one win out and in all cases the desired transaction is accomplished.

The former constitutes a potentially severe DOS attack. The latter would not be that big a deal (in my own use-case and as far as I currently understand.)

Or is it the case currently that the end result of an intercept+modify_hash+redistribute attack would be somewhat left to chance due to differences in the protocol implementation and such-like.

Before there were griefers on the network mutating transactions it was safe to spend your own unconfirmed change, because you could reasonably assume that you weren't going to invalidate your own transaction.

Now it's no longer safe. because you don't know what version of your transaction is going to make it into the blockchain, therefore any transactions you make that reference unconfirmed change will fail.

This is bad news for wallets that do not manage their outputs well. I'm interested in seeing how these single-key wallets like blockchain.info are affected. Any wallet that tries to keep its entire balance in a single utxo is going to only be usable for spends once per block.

Thanks for the input. Are you quite sure that that is empirically the case, or is it more theoretical? (That is, transactions work as always whether attacked or not, but one must rely on confirmation rather than transaction hash?)

For my part, I rarely make more than one spend per block cycle. I'd be totally fine not spending unconfirmed outputs and would be totally fine doing my planning to adhere to such a policy. I typically only make a handful of transactions per month (if that) and feel pretty guilty about every spend I make since they are highly subsidized. I voluntarily pay an unusually high transaction fee.

I'd be delighted to do a bulk of my petty spending work in an off-chain solutions which avoided spamming the global block-chain. As soon as one which is reliable and trustworthy appears, I'll jump eeen it!