What is X17?

X17 is a chained hashing algorithm that extends the X-series family to its longest standard variant, sequentially applying seventeen different cryptographic hash functions. Building upon X15, X17 adds two more hash functions — Haval and SHA-256 — to create the most comprehensive chain in the X-series lineage. The complete sequence processes data through BLAKE, BMW (Blue Midnight Wish), Groestl, JH, Keccak, Skein, Luffa, CubeHash, SHAvite-3, SIMD, ECHO, Hamsi, Fugue, Shabal, Whirlpool, Haval, and SHA-256 in order. Each function receives the output of its predecessor, creating a 17-stage pipeline where the input is progressively transformed through diverse cryptographic operations.

X17 inherits the security philosophy of its X-series predecessors while maximizing the defense-in-depth approach by employing the largest number of independent hash functions. The seventeen-algorithm chain makes ASIC development particularly expensive and complex, as a custom chip must efficiently implement all seventeen different algorithms to provide any mining advantage. This creates significant barriers to entry for hardware manufacturers and was designed to keep mining accessible to GPU miners for longer than shorter-chain alternatives. The algorithm provides strong collision resistance through the cumulative effect of its many processing stages, and a vulnerability in any single component function is mitigated by the sixteen remaining functions. However, the longer chain also increases computation time per hash, which affects the overall mining throughput and energy efficiency compared to simpler algorithms.

X17 was introduced in 2014 as part of the ongoing expansion of the X-series algorithms that began with X11 in Dash. It was adopted by several cryptocurrency projects, including Verge (XVG), which used X17 as one of its five available mining algorithms in its multi-algorithm mining approach. Verge's implementation allowed miners to choose between Scrypt, X17, Lyra2rev2, Myr-Groestl, and BLAKE2s, with the network adjusting difficulty independently for each algorithm. Other smaller projects also adopted X17 during the 2014-2016 period of intense algorithm experimentation in the cryptocurrency space. X17 represents the practical upper limit of the X-series approach — while theoretically more hash functions could be added, the diminishing returns in security versus the increasing computational overhead made further extensions less attractive. The algorithm stands as the culmination of the chained-hash paradigm that the X-series made popular in cryptocurrency mining.