What is C11?

C11 is a proof-of-work hashing algorithm that chains together 11 cryptographic hash functions in a fixed sequence: BLAKE, BMW (Blue Midnight Wish), Groestl, JH, Keccak, Skein, Luffa, Cubehash, SHAvite, SIMD, and ECHO. While it uses the same number of hash functions as X11, C11 employs a different selection and ordering of algorithms, creating a distinct computational profile. The input data passes through each of the 11 functions sequentially, with the output of each serving as the input to the next, resulting in a deeply layered hash that leverages the individual strengths of each cryptographic primitive.

Like other multi-algorithm chains, C11 provides security through cryptographic diversity — the probability that critical vulnerabilities exist simultaneously in all 11 independent hash functions is extremely low. The algorithm offers moderate ASIC resistance, as implementing 11 different hash functions in a single chip requires significantly more silicon area and design complexity than a single-algorithm ASIC. C11 performs well on GPUs, where the parallel processing capabilities can handle the sequential hash chain efficiently. The power consumption during C11 mining is generally moderate, positioned similarly to X11 in terms of energy efficiency, as the diverse operations prevent any single computational unit from being constantly stressed.

C11 was introduced as an alternative to X11, aiming to differentiate itself through its particular combination and ordering of hash functions while maintaining a similar philosophy of multi-algorithm security. It has been used by several smaller cryptocurrency projects, including Chaincoin (CHC), which adopted C11 as its primary proof-of-work algorithm. Chaincoin gained brief attention during the 2017 cryptocurrency boom as a masternode-focused project. While C11 has not achieved the widespread adoption of X11 or X13, it occupies a meaningful position in the evolution of chained hash algorithms, demonstrating that varying the selection and sequence of well-known hash functions can create viable alternative proof-of-work schemes with their own performance characteristics.