I have done some financial analysis to see how fast an attacker can get benefit from this attack. Let's the total network hashing rate is stable. At the beginning of the attack, he will always loss some mining revenue as the diff is fixed and he will lose some blocks when he is trying to broadcasting his double blocks. And his attack will make the growth of blockchain slow.
If the attacker owns 30% of the network hashing power, according to the formula of on the paper ten, he will make the blockchain grows 1.8x slower than if not attacked. Assuming 50% of the block attacker broadcasts accepted, The revenue speed of the attacker will be influenced. He will loss 40% of his revenue if he had not attack, which is to make other honest miner mine even less and more slower. If the attack continues to next diff period, the attacker start to enjoy the benefit. He will earn more than 9% if he had not attack.
The attack invest 1.8*14=25 days time and 40% of the mining revenue (3600*25*30%*40%=10800 BTC, assuming still 25 btc per block), and he can earn more than 100BTC everyday, which earns investment in 111 days, during which time the whole community finds out his naughty behavior and make a hard-fork.
So, not a very wisdom attacker.
Please check whether my logic is right or wrong by independent calculation. Assuming the total net work hashrate is stable to make analysis simpler. First the attacker has to invest time and losing mining revenue to slow down other people, however the diff is fixed during the time, he is losing money to attack the network. The chain will grow extremely slower during the attack. The attacker suffers with other honest miner together, much longer than 14 days. If he is wealth enough and willing enough, Diff lowers, and he starts to harvest the benefit. However, the time to make his investment back is very long, and before he can earn back his investment, the community will have already make a hard-fork.
+1If the attacker owns 30% of the network hashing power, according to the formula of on the paper ten, he will make the blockchain grows 1.8x slower than if not attacked. Assuming 50% of the block attacker broadcasts accepted, The revenue speed of the attacker will be influenced. He will loss 40% of his revenue if he had not attack, which is to make other honest miner mine even less and more slower. If the attack continues to next diff period, the attacker start to enjoy the benefit. He will earn more than 9% if he had not attack.
The attack invest 1.8*14=25 days time and 40% of the mining revenue (3600*25*30%*40%=10800 BTC, assuming still 25 btc per block), and he can earn more than 100BTC everyday, which earns investment in 111 days, during which time the whole community finds out his naughty behavior and make a hard-fork.
So, not a very wisdom attacker.
Please check whether my logic is right or wrong by independent calculation. Assuming the total net work hashrate is stable to make analysis simpler. First the attacker has to invest time and losing mining revenue to slow down other people, however the diff is fixed during the time, he is losing money to attack the network. The chain will grow extremely slower during the attack. The attacker suffers with other honest miner together, much longer than 14 days. If he is wealth enough and willing enough, Diff lowers, and he starts to harvest the benefit. However, the time to make his investment back is very long, and before he can earn back his investment, the community will have already make a hard-fork.
This is the kind of analysis that I think we need more of before jumping to the conclusion that there is actually a problem that needs to be fixed. I'm not claiming that HorseRider is correct, but his logic looks plausible and I tend to listen harder to reasonable people who say things like "please check whether my logic is right".