X11 is the name of the chained proof-of-work (PoW) algorithm that was introduced in Darkcoin (launched January 18th, 2014). It was probably inspired by the chained-hashing approach of Quark, adding further “depth” and complexity by increasing the number of hashes, yet it differs from Quark in that the rounds of hashes are determined a priori instead of having some hashes being randomly picked.

The X11 algorithm uses multiple rounds of 11 different hashes (blake, bmw, groestl, jh, keccak, skein, luffa, cubehash, shavite, simd, echo), thus making it one of the safest and more sophisticated cryptographic hashes in use by modern cryptocurrencies.

The name X11 is not related to the open source GUI server that provides a graphical interface to unix/linux users.

  • 1 Advantages of X11
    • 1.1 Increased confidence and safety for currencies
    • 1.2 ASIC resistance
    • 1.3 Multipool resistance
    • 1.4 Balanced CPU/GPU mining
    • 1.5 Reduced energy draw and heat output from GPUs
  • 2 Mining with X11
  • 3 Litecoin X11 fork threat
  • 4 List of X11 Coins

Advantages of X11

Increased confidence and safety for currencies

The increased complexity and sophistication of the chained algorithm provides enhanced levels of security and less uncertainty for a digital currency, compared to single-hash PoW solutions that are not protected against security risks like SPOF (Single Point Of Failure).

For example, a possible but not probable (for the short or mid-term future) computing breakthrough that “breaks” the SHA256 hash could jeopardize the entire Bitcoin network until the network shifts through a hard fork to another cryptographic hash.

In a similar scenario of computing or cryptographic breakthrough, a digital currency using the X11 PoW chained hashing would have to experience a simultaneous collapse for all of its elevel hashes in order for the network to be “broken”, something which is extremely improbable. Even if some of the 11 hashes prove unreliable, in the mid-to-long term, there will be adequate warning for a currency using X11 to take measures and replace the problematic hashes with other more reliable hashing algorithms.

Given the speculatory nature of digital currencies and their inherent uncertainties as a new field, the X11 algorithm can provide increased confidence for its users and potential investors that single-hash approaches cannot: While Bitcoin and Litecoin dominate the market capitalization of cryptocurrencies, they have been unable to convince a large number of ordinary people and investors of their ability to overcome a potential flaw or catastrophic failure of their encryption that could make their value plummet and jeopardize the faith on the currency. Chained hashing solutions, like X11, provide increased safety and longevity for store of wealth purposes, investment diversification and hedging against risks associated with single-hash currencies plagued by SPOF (Single Point Of Failure).

ASIC resistance

Application-specific integrated circuits (ASICs) have become one of the most hated aspect of the cryptocurrency movement by most cryptocurrency adopters due to the belief that ASICs centralize the hashing power of a network which will worsen the prospects of a cryptocurrency network to protect itself against a 51% collusion attack.

Bitcoin was initially mined only through CPUs (the central processors found in PCs and laptops), then through GPUs (graphical processors found on graphic adapters) and finally through custom-made ASIC-based devices that accelerated mining a few orders of magnitude compared to CPUs and GPUs.

Litecoin tried to solve the problem of ASIC resistance through increased memory access of its own scrypt hash that would give CPU users (and later on GPU users) far better chances of decentralizing the mining resources. However, as of Q1 2014, ASICs have been developed for scrypt-based digital currencies which have raised concerns on whether it is even possible to offer ASIC resistance.

At this point of time (March 2014), X11 is fully ASIC-resistant/ASIC-immune as there are no ASIC implementations for it. The advanced sophistication of X11 (11 hashes combined instead of 1), will require a more complex ASIC design compared to those used for single-hash PoW. Even if ASICs are eventually deployed at some future point, it is possible that these will not be able to achieve the same degree of acceleration that was achieved in single-hashing algorithms like SHA256 as ASICs excel in paralleling workloads of decreased complexity. On the other hand, the 11 hashes comprising the X11 algorithm can theoretically be programmed very efficiently on a hardware level (FPGAs/ASICs) although the slowest hash is the one which will ultimately determine the highest speed of any hardware implementation.

Evan Duffield, the creator of Darkcoin and X11 chained-hash, has wrote on several occasions that X11 was integrated into Darkcoin not with the intention to prevent ASIC manufacturers from creating ASICs for X11 in the future, but rather to provide a similar migratory path that Bitcoin had (CPUs, GPUs, ASICs). He expects that eventually, as Darkcoin grows in market capitalization, and ASIC investments becomes profitable, ASICs will be developed.

Multipool resistance

Due to being different than the established SHA256 & Scrypt coins, X11 requires a different mining client which disallows Scrypt-based multipools to mine it. So, in effect, a multipool can either mine Scrypt or X11 but not both.

Multipools are mining pools that hop from coin to coin in order to achieve the maximum profit for the miners, in terms of bitcoins per day. Multipools shift their hashrate depending the difficulty factor and profitability of alternative cryptocurrencies and thus the networks of such cryptocurrencies experience tremendous swings in their hashrate. More importantly, the market value of such cryptocurrencies is significantly affected due to a large volume of selling action that follows the engagement of multipools, as the coins mined are sold in the various exchanges for bitcoins.

The first X11 multipools appeared on April 2014, alternating between Darkcoin and Hirocoin. By late May 2014 some big multipools had changed their setup to X11 mining with hundreds of gigahases of computing power.

Balanced CPU/GPU mining

When Darkcoin was initially launched with X11, it was only mineable through CPU mining programs. After a spike in the Darkcoin network hashrate in early February 2014, it was speculated that someone might have made a GPU miner and thus a bounty of over 3000 DRKs was given in order to assist in the creation of a GPU miner client that could be publicly available, for fairness reasons.

By mid-February the GPU client was launched and by late-February it was optimized for higher hashrates. At the same time, the CPU mining clients evolved to increase their speed by using the SSE2/3/4, AVX and AES instruction sets.

At that point it became evident that the hashrate difference between GPU and CPU implementations were not that chaotic, although GPUs still took the crown in terms of energy efficiency. Top of the line and tuned CPUs, like a 6-core i7s running at 4.5 GHz produced 880 khashes/second when GPUs like AMD’s 280 and 290 gave 3 times as much.

A ratio of 1:3 was thus established for the fastest CPUs versus the fastest AMD GPUs – which is significantly better than Scrypt or SHA256 and allowing CPU users to mine X11 coins.

It should be noted that these ratios are more a reflection of the mining programs rather than an inherent property of the algorithm itself and thus the ratios can change depending the development progress of the CPU and GPU mining clients.

Update: As of May 15th 2014, a new Nvidia miner (ccminer with X11 support) has allowed hashrates of up to 5 Mh/s for a 780 Ti. This means that the ratio of highest CPU vs highest GPU is now closer to 6.0x.

Reduced energy draw and heat output from GPUs

With the arrival of the X11 GPU mining program, many Darkcoin miners discovered that their GPU temperatures were significantly reduced, fan noise was down and power draw was reduced by 30% to 55% for AMD GPUs.

While this should not be considered a property of X11 itself as the algorithm is hardware-agnostic, X11 has gained much favor from miners who had high electricity costs, heat issues and noise issues while mining Scrypt-based cryptocurrencies. Some GPU miners have reported that they are now able to sleep better due to the GPU fans not making as much noise as they did with Scrypt coins.

It is theoretically possible that the reduced energy draw and heat output from GPU miners could change to a more “normal” level, if and when the GPU mining program is further optimized.

Mining with X11

Mining information regarding X11 can be found in the Mining Darkcoin page, although this is a Darkcoin-specific page and does not cover mining pools of other cryptocurrencies. In general, X11 mining should be pretty similar among all X11 coins.

The following mining programs can mine X11 coins for Linux and Windows:


Source for minerd 1.2c (SSE2): https://github.com/ig0tik3d/darkcoin-cpuminer-1.2c

Source for minerd 1.3 (SSE4/5/AVX/AES-NI): https://github.com/elmad/darkcoin-cpuminer-1.3-avx-aes

Windows miner for systems with no SSE2 instruction set: http://darkcoin.io/downloads/xcoin-miner.zip

Windows miner (1.2c) for SSE2 systems: http://darkcoin.io/downloads/darkcoin-minerd-1.2c.zip

Windows miner (1.3) for SSE4-5-AVX-AES-NI systems: http://download.darkcoin.fr/darkCoin-cpuminer-1.3-avx-aes-windows-binaries.zip


Source: https://github.com/prettyhatemachine/sph-sgminer

Windows: https://mega.co.nz/#!2JYXHDpD!OOiFOdsh5rnvk1zhz5niXENNzbgnw1UXwmFcicBzevI

Sph-Sgminer thread on bitcointalk.org for support and latest Windows builds: https://bitcointalk.org/index.php?topic=475795.0

GPU (Nvidia):

CCminer with X11 support: http://cryptomining-blog.com/2361-new-ccminer-1-0-available-with-added-support-for-x11-mining/

Litecoin X11 fork threat

On March 30, 2014, a user of Bitcointalk forum claiming to represent a group (“LTC X11 team”) of GPU miners, developers and people who are concerned about the future of Litecoin as an ASIC-resistant currency, wrote about his intention to fork the LTC network on block #564,480. The fork would change the PoW algorithm from Scrypt to X11, thus having two Litecoins in circulation at the same time: One with Scrypt and one with X11.

He claimed that with support from the miners and the exchanges, the fork would become prevalent in the end, making the Litecoin-Scrypt fork obsolete.

The Litecoin developers issued an official response refusing such a change, saying that adopting a different PoW algorithm was not something that can be easily done at this stage of the coin’s life without massively hurting confidence in it.

List of X11 Coins

There are a number of X11 coins beyond Darkcoin.

  • CATicoin
  • Edgecoin
  • ElectronicYen
  • Electronic LIRA
  • Emirates Coin
  • Europecoin
  • GiveCoin
  • Global Denomination
  • HashCoin
  • HighFiveCoin
  • Hirocoin
  • Juggalocoin
  • Limecoin
  • Logicoin
  • Muniti
  • Nyancoin
  • Quebecoin
  • SummerCoin
  • TwilightCoin
  • VirtualCoin
  • X11Coin

Note: The above list is not not being updated given that there are at least 10 new coins per month that feature X11.