  Bitcoin-NG, a scalable blockchain protocol, divides each block into a key
block and many micro blocks to effectively improve the transaction processing
capacity. Bitcoin-NG has a special incentive mechanism (i.e. splitting
transaction fees to the current and the next leader) to maintain its security.
However, this design of the incentive mechanism ignores the joint effect of
transaction fees, mint coins and mining duration lengths on the expected mining
reward. In this paper, we identify the advanced mining attack that deliberately
ignores micro blocks to enlarge the mining duration length to increase the
likelihood of winning the mining race. We first show that an advanced mining
attacker can maximize its expected reward by optimizing its mining duration
length. We then formulate a game-theoretical model in which multiple mining
players perform advanced mining to compete with each other. We analyze the Nash
equilibrium for the mining game. Our analytical and simulation results indicate
that all mining players in the mining game converge to having advanced mining
at the equilibrium and have no incentives for deviating from the equilibrium;
the transaction processing capability of the Bitcoin-NG network at the
equilibrium is decreased by advanced mining. Therefore, we conclude that the
Bitcoin-NG blockchain protocol is vulnerable to advanced mining attack. We
discuss how to reduce the negative impact of advanced mining for Bitcoin-NG.
