Double spend alert system

[jl2012]

After the double spend attack against OKPAY, I think we need an automatic double spend alert system.

First of all, the definition of double spend is "the existence of two different valid transactions which the inputs are common or partially common"

Currently, a node will ignore double spend transactions and not relying them. However, the more logical way of handling double spend transactions should be broadcasting the conflicting transactions, so everyone will know there is a double spend.

When double spend is identified, miners will stop mining any transactions from the same address for at least 48 hours. Warning message will pop up at the clients of the recipients.

If there were a system like this, the double spend attack against OKPAY would not be successful unless the attacker mines his own block.

There are some special issues with this system:

1. If there are 2 transactions which the inputs and outputs are exactly the same, but one of them with an extra input which the BTC is sending to nowhere (i.e. miner fee), it won't be considered as double spend attack. Sometimes people may send transactions with inadequate miner fee and this will allow them to add more fee.

2. Greedy miners may still mine for double spend transactions if a huge amount of fee is included.

3. There is a possible DoS attack by flooding the network with infinite double spend transactions

[Mike Hearn]

There was a paper published last year which proposed such a thing and analyzed it. I think everyone agrees it's a good idea, just somebody needs to make it happen.