ASIC resistant describes a mining algorithm designed so that an Application-Specific Integrated Circuit (ASIC) gains little or no advantage over general-purpose hardware such as a graphics processing unit (GPU) or an ordinary processor. The aim is to keep crypto mining open to people with everyday computers and to stop a few chip makers from dominating a network.
ASIC resistance is a goal, not a guarantee. Several algorithms once described as resistant were later beaten by specialised hardware. The best-known current example is RandomX, used by Monero; the best-known historical one is Ethash, used by Ethereum (ETH) until it stopped mining in 2022.
ASIC resistant in plain terms
Imagine a race in which a purpose-built racing car would always beat ordinary family cars. One way to keep the race open is to change the course: add sharp turns, mud and a stretch where every car must carry a heavy load. Now the racing car's special engine helps much less, and the family cars can compete.
ASIC-resistant algorithms change the "course" of mining. Instead of a pure speed test, they force machines to read and write large amounts of memory or to run varied, unpredictable instructions, tasks that ordinary computers already do well and that are expensive to build into a single-purpose chip.
How resistance is attempted
Bitcoin's SHA256 needs almost no memory and repeats one fixed calculation, which is ideal for custom chips. Resistant designs use one or more of these techniques:
- Memory hardness. The algorithm requires each hash to fetch data from a large block of memory, so performance is limited by memory bandwidth, which custom chips cannot easily improve. Scrypt and Ethash both took this approach.
- Random programs. The algorithm generates a different random program for each attempt and runs it, so efficient hardware must look like a general-purpose CPU. RandomX works this way.
- Periodic changes. A project commits to changing its algorithm through a hard fork whenever ASICs appear, making investment in custom chips risky.
Track record
The history is mixed:
- Scrypt. Litecoin (LTC) adopted Scrypt in 2011 partly to favour ordinary hardware, but Scrypt ASICs were on sale by 2014. Litecoin did not change course, and it and Dogecoin (DOGE) are now mined mostly with ASICs.
- Ethash. Ethereum's algorithm relied on a large and growing dataset held in memory, known as the DAG. In April 2018 Bitmain confirmed it was selling an Ethash ASIC, though graphics cards remained a large share of Ethereum mining. A proposed replacement, ProgPoW (EIP-1057), was debated in 2019 and 2020 but never activated, and mining ended when Ethereum moved to Proof of Stake (PoS) on 15 September 2022. Ethereum Classic (ETC) still uses a variant of Ethash.
- Monero. After ASICs for its CryptoNight algorithm appeared in 2018, Monero changed the algorithm several times through scheduled upgrades, then switched to RandomX on 30 November 2019 at block 1,978,433. RandomX is optimised for ordinary CPUs and has so far kept Monero mining on general-purpose computers.
- Equihash. Used by Zcash, it was designed to be memory-hard, but Equihash ASICs were released in 2018. Bitcoin Gold (BTG), a 2017 Bitcoin fork created to make mining accessible to GPUs, later changed its own Equihash settings in response.
Arguments for and against
Supporters of ASIC resistance argue that it:
- Spreads mining more widely, because anyone with a gaming PC or server can take part, supporting decentralisation.
- Reduces dependence on a handful of hardware makers who might influence a network's direction.
- Allows mining with hardware that keeps its value for other uses, reducing electronic waste.
Critics reply that it:
- Lowers the cost of attack. If an algorithm runs on widely available hardware, an attacker can rent cloud servers or a botnet to mount a 51% attack, especially on smaller networks; ASIC-mined chains are protected by hardware that has no other use.
- Invites malware. CPU-friendly coins are popular with cryptojacking software that secretly mines on victims' computers.
- Only delays the inevitable. Any profitable calculation can eventually be built into specialised chips, and frequent algorithm changes increase the risk of bugs and chain splits, which is one reason the Bitcoin (BTC) community has never pursued it.
For a coin's holders, ASIC resistance shapes who earns new coins, how hashrate is distributed and which mining rig designs are viable. Whether resistance holds depends on economics as much as engineering: the larger a coin's mining rewards, the stronger the incentive for someone to build specialised hardware for it. It is one design choice among several for mineable coins built on Proof of Work (PoW).