What happened
MonaCoin (MONA), a Japanese proof-of-work cryptocurrency, was hit by a selfish-mining attack between May 13 and 15, 2018 that caused about $90,000 in losses. A miner controlling up to 57% of the network's hashrate mined blocks in secret while spending MONA on the public chain, moving coins through offshore exchanges including Livecoin to swap them for other cryptocurrencies. The miner then released its longer hidden chain, which invalidated blocks other miners had produced in the meantime.
MonaCoin developers said on May 18 that they had a grasp of the attack, and it had stopped by May 19. Many exchanges froze MONA deposits while they worked on defenses. Coins held in users' own wallets were reported to be safe.
The attack came in the same month as 51% attacks on Verge and Bitcoin Gold.
How it happened
- The attacker gathered enough mining power to control up to 57% of MonaCoin's hashrate.
- It mined a private chain of blocks without broadcasting them.
- On the public chain, it sent MONA to exchanges such as Livecoin and swapped the coins for other cryptocurrencies before the hidden chain was revealed.
- It published its longer private chain. Nodes follow the chain with the most work, so the public blocks from other miners were invalidated. The damage was estimated at about $90,000.
Protocol details
Evidence
- analysis DeFiLlama defillama.com
- analysis Japan's Monacoin falls victim to malicious mining attack (CoinGeek) coingeek.com
- analysis Japanese Cryptocurrency Monacoin Hit by Selfish Mining Attack (CCN via Yahoo Finance) finance.yahoo.com
- analysis Self-serving cryptocurrency miners are attacking small blockchain networks (MIT Technology Review) technologyreview.com
- analysis monacoin.org page monacoin.org monacoin.org
Build your security review skills
Work through hands-on labs covering real exploit mechanics, review techniques, and defensive patterns.
