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Implications

The aforementioned attack can have serious implications on the Bitcoin network.

Implication 1: The adversary can increase its advantage in selfish mining (see Section 4.1.4.1), by splitting the mining power of the honest nodes. Implication 2: The adversary can double-spend transactions even if these transactions are confirmed by six consecutive blocks. For example, the victim can be a merchant and the adversary can simply pay him, eclipse the miners working on confirming this transaction, and then issue a double-spending transaction to uneclipsed miners. Since the blocks performed by eclipsed miners will be eventually obsolete, this attack is likely to succeed.

Countermeasures

Heilman et al. suggest a number of countermeasures to thwart this attack: Countermeasure 1: One possible hardening technique is to ensure that the same address hashes to the same bucket and the same location in the tried table. By doing so, one can prevent the adversary from reusing the same address more than once to fill the tried table.

Countermeasure 2: Another countermeasure would be to simply avoid any bias in choosing addresses that are recent. Currently, there is a bias in choosing recently time-stamped addresses, which will increase the probability to connect to the adversary’s addresses.

Countermeasure 3: Another basic countermeasure would be to ensure that an IP address exists (e.g., by attempting to ping/connect to it) before overwriting an older address in the tried and new.

Countermeasure 4: One possible countermeasure would be to simply add new buckets, which will harden the realization of such attacks.

Countermeasures 1, 2, and 4 have been integrated in the official Bitcoin client v0.10.1.

Note that in [2], the adversary needs to have almost 5120 IP addresses at his or her disposal to eclipse a victim. Moreover, the adversary would need clients to restart. Recently, Gervais et al. [4] have however shown that even resource- constrained adversaries can perform similar eclipse attacks without requiring any node restart. Namely, the authors show that the adversary can abuse existing scalability measures adopted in Bitcoin in order to deny information about transactions to Bitcoin nodes for a considerable amount of time. In what follows, we sketch out this attack and outline a number of countermeasures.

 
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