2018 double-spend attacks on Equihash-based cryptocurrencies

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Between May and June, 2018, a number of cryptocurrencies based on Equihash algorithm and PoW consensus mechanism, Bitcoin Gold,[1] ZenCash,[2] Zcash and Litecoin Cash,[3] suffered from 51% double-spend attacks.

Affected cryptocurrencies[edit]

Bitcoin Gold (BTG)[edit]

In May, 2018, unknown attackers successfully committed a double-spend attack on Bitcoin Gold, a forked cryptocurrency from Bitcoin in 2017. An amount of approximately $18.6 million USD worth of Bitcoin Gold was stolen.[4][5][6][7]

On bitcoingold.org forum, the director of communications, Edward Iskra, wrote:

An unknown party with access to very large amounts of hashpower is trying to use “51% attacks” to perform “double spend” attacks to steal money from Exchanges. We have been advising all exchanges to increase confirmations and carefully review large deposits.

ZenCash (ZEN)[edit]

ZenCash announced its network suffered a from 51% attack on June 2 and executed migrations to increase the difficulty for attack:

The ZenCash network was the target of a 51% attack on 2 June at approximately 10:43 pm EDT (03 June 02:43 hrs UTC). The ZenCash team immediately executed mitigation procedures to significantly increase the difficulty of future attacks on the network.


Per zdnet.com reports,[8] a website Crypto51[9] is setup to show the cost and difficulty to commit 51% double-spend attack for all PoW cryptocurrencies. In addition, a study by the University of Luxembourg found that up to 30% of the entire hashpower on Equihash-based coins were from high-efficiency ASIC miners, which could explain the unprecedented rise of successful attacks on algorithms once ASIC resistant.[10]


  1. ^ "Double Spend Attack on Exchanges". The Bitcoin Gold Community Forum. Retrieved 2018-06-05.
  2. ^ "ZenCash Statement on Double Spend Attack - ZenCash". ZenCash. 2018-06-03. Retrieved 2018-06-05.
  3. ^ "Blockchain's Once-Feared 51% Attack Is Now Becoming Regular - CoinDesk". CoinDesk. 2018-06-08. Retrieved 2018-06-09.
  4. ^ "Bitcoin Gold loses millions as it is hit by a double spend attack". Fast Company. 2018-05-24. Retrieved 2018-05-27.
  5. ^ Osborne, Charlie. "Bitcoin Gold suffers double spend attacks, $17.5 million lost | ZDNet". ZDNet. Retrieved 2018-05-27.
  6. ^ "Responding to Attacks - Bitcoin Gold". Bitcoin Gold. 2018-05-24. Retrieved 2018-05-27.
  7. ^ "Bitcoin Gold Responds to Recent Double Spend Attack". CCN. 2018-05-25. Retrieved 2018-05-27.
  8. ^ Osborne, Charlie. "Bitcoin Gold suffers double spend attacks, $17.5 million lost | ZDNet". ZDNet. Retrieved 2018-06-09.
  9. ^ "Cost of a 51% Attack for Different Cryptocurrencies | Crypto51". www.crypto51.app. Retrieved 2018-06-09.
  10. ^ "University of Luxembourg: 30% of Equihash Hashrate is ASIC Miners, Enabling 51% Attacks - Chainstate". Chainstate. 2018-06-15. Retrieved 2018-06-16.