Equihash is a memory-hard Proof of Work algorithm.
How Equihash is functioning?
It was introduced by the University of Luxembourg’s Interdisciplinary Center for Security, Reliability and Trust (SnT) at the 2016 Network and Distributed System Security Symposium.
The algorithm is based on a generalization of the Birthday Problem which finds colliding hash values. It was designed such that parallel implementations are bottle-necked by memory bandwidth in an attempt to worsen the cost-performance trade-offs of designing custom ASIC implementation. The ASIC Resistance of Equihash is based on the assumption that commercially-sold hardware already has quite high memory bandwidth, so improvements made by custom hardware may not be worth the development cost.
Is Equihash still a succesful algo versus the ASICs ?
Unfortunately there were ASICs that have been finally designed for mining the Equihash algo. They have wide availability in the market, because Equihash became really popular. Specifically the manufacturer Bitmain succeeded in optimizing the processing of Zcash’s Equihash-200,9 with an ASIC.
Some Cryptocurrency projects like BitcoinZ, BitcoinGold and ZEL tried to switch to altered Equihash algo variances that could keep their resistance to the ASIC miners. The BitcoinZ Community pioneered with its Equihash variance called “ZHash” making its network resistant to Bitmain’s offerings.