As there are more than
1.8 million bitcoins that have not been moved since they were mined, isn't it possible that someone rebuilds the entire blockchain in order to claim those bitcoins? This attacker could even keep all transactions made till today, so people would not lose their balance.
It would
take 200 days with the present hashrate to rebuild the entire blockchain. So, for instance, if someone invest in mining facilities equivalent to double the present hashrate (a lot of money, but not impossible), it would take 200 days to create a new blockchain with more work than the original one (100 days to have the same work as it has today and other 100 days as the blockchain would be bigger by then).
Comparing the alternatives, with that amount of hash rate:
1) If the attacker mined in the original blockchain, he would obtain 240,000 bitcoins in 200 days (1,800 btc/day * 200 days * 2/3 of total hash rate), probably at a loss.
2) If he performs the attack, he would obtain 1,800,000 bitcoins.
So, the incentives are pro-attack. Also, those incentives are expected to be greater in the future, as the block reward gets smaller.
What do you think about this? Is there something I am missing here?
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