What is X13?

X13 is a chained hashing algorithm that extends the X11 design by adding two additional cryptographic hash functions to the sequence, bringing the total to thirteen. The chain includes all eleven functions from X11 — BLAKE, Blue Midnight Wish, Grøstl, JH, Keccak, Skein, Luffa, CubeHash, SHAvite-3, SIMD, and ECHO — followed by Hamsi and Fugue. Input data passes through all thirteen functions sequentially, with each hash output serving as the input for the next function in the chain, creating an even more layered security structure than its predecessor.

By incorporating two additional hash functions beyond X11, X13 further strengthens the defense-in-depth approach to cryptographic security. The greater number of chained algorithms increases the computational complexity required to develop specialized mining hardware, which provided enhanced ASIC resistance compared to X11 during the early years. The algorithm maintains good energy efficiency while offering a higher level of redundancy — a vulnerability discovered in any single hash function has minimal impact on the overall security of the chain. Like other multi-algorithm designs, however, the ASIC resistance was not permanent, as hardware manufacturers adapted to support increasingly complex algorithm chains.

X13 emerged in 2014 as part of the wave of X-series algorithms inspired by X11's success with Dash. It was adopted by several cryptocurrencies seeking to differentiate from both Bitcoin's SHA-256 and the increasingly popular X11. Notable cryptocurrencies that have used X13 include Stratis (in its original proof-of-work phase before transitioning to proof-of-stake), MaruCoin, and several other altcoins from the 2014-2015 era. While X13 never achieved the same level of adoption as X11, it served as an important stepping stone in the evolution toward even more complex chained algorithms like X15 and X17.