What is CryptoNight?

CryptoNight is a memory-hard proof-of-work hashing algorithm developed as part of the CryptoNote protocol, first described in a whitepaper published under the pseudonym Nicolas van Saberhagen in 2013. The algorithm works by initializing a large scratchpad of approximately 2 MB in memory, then performing a long sequence of read-modify-write operations at pseudo-random addresses within this scratchpad. This memory-intensive approach forces miners to maintain fast access to a significant block of memory throughout the entire computation, making the algorithm fundamentally dependent on memory latency and cache performance rather than raw computational throughput.

The defining property of CryptoNight is its strong egalitarian mining design, specifically targeting CPU efficiency. The 2 MB scratchpad was chosen to fit within the L3 cache of most modern CPUs, giving consumer processors a natural advantage. This design made it impractical for GPUs (which have many cores but limited per-core cache) and extremely difficult for ASICs to implement efficiently, as replicating fast 2 MB scratchpads across many parallel units is prohibitively expensive in silicon. CryptoNight also incorporates AES encryption rounds as part of its computation, leveraging the AES-NI hardware instructions found in modern x86 processors for additional CPU optimization.

CryptoNight was first used by Bytecoin, the original CryptoNote implementation launched in 2012, but gained widespread prominence through Monero, which launched in April 2014 and became the leading privacy-focused cryptocurrency. Monero maintained a policy of regular algorithm modifications (CryptoNight-V1, V2, CryptoNight-R) to actively resist the development of ASIC miners, before eventually transitioning to RandomX in November 2019 for even stronger ASIC resistance. Other cryptocurrencies that used variants of CryptoNight include Electroneum, Haven Protocol, Aeon, and Karbo, forming a broad family of privacy-oriented coins built on the CryptoNote foundation.