Coinbase limits Zcash trading as ViaBTC poses risks of 51% attack

Coinbase changed the Zcash confirmation requirement to 110 blocks, increasing deposit time from 40 minutes to 2.5 hours.

Crypto exchange Coinbase has limited trading with Zcash (ZEC) after it found that a single mining pool now controls more than 50% of Zcash’s hash power.

In a blog post on Sept. 15, Coinbase said it increased the number of network confirmations required for processing deposits and moved our ZEC trading markets into a limit-only mode to reduce the impact of any volatility.

Now, Coinbase waits for 110 blocks to be confirmed by the network, which means users would have to wait about 2.5 hours to deposit ZEC into the exchange.

Block distribution in Zcash | Source: MiningPoolStats

According to data from MiningPoolStats, ViaBTC is now controlling 53% of the Zcash hashing power, while unknown entities control 18.3% and AntPool — 12.2%. Coinbase says it has reached out to Electric Coin Company (ECC), the team behind Zcash, and ViaBTC to reduce the risks of an attack against the network.

“We shared our concerns around the risks of mining centralization and provided recommendations for various options that either party could implement to reduce the risk of a 51% attack.”


It is viewed as a mortal threat to the concept of decentralization. To launch a 51% attack, a person must control most of a network’s mining power and use that power to alter recorded transactions. However, large cryptocurrencies like Bitcoin (BTC) are incredibly difficult to attack because of the resources and hardware it would take.

As of press time, neither ECC nor ViaBTC made any public statements. Once a single miner or mining pool gets over 51% of the network’s hash power, it posts risks of the so-called 51% attack.

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