One of the most popular articles on this blog is about Kimoto’s Gravity Well. However, it is also somewhat outdated by now. We are living in an age of rapid innovation in altcoins. They are quickly adapting to the multipool threat. The new state of the art is even better than Gravity Well.
The recently launched HeavyCoin comes with a technique called Temporal Retargeting. The idea is quite simple. Whenever a block is much overdue, the difficulty drops automatically without waiting for the block to be finished. The network accepts a proof-of-work with lower difficulty and moves on:
In Heavycoin, the network will begin to self-heal by lowering the difficulty if no block is found after a significant amount of time. However, to guarantee security, the self-healing time threshold is selected so that an adversary cannot manipulate the network in order to lower the difficulty artificially.
Dogecoin recently (version 1.6) also got some multipool defense. The multipools snatched away the bonus blocks, which turned out to be not so random. Dogecoin had help from the DigiByte community in the form of DigiShield:
With our own custom implementation we have tested many different variations on how far the difficulty is allowed to jump each block. The more we allow the difficulty to jump, the faster it adapts. Pretty much every scrypt based coin out there only allows a jump by a factor of 4 within a block retarget. […] We feel pushing this up from a factor of 4 to a factor of 200-2000 is the way to go. This allows for very dramatic adjustments with every block which means very quick adjustments to hash movements. This approach has far out performed the Gravity Well or Earthcoin code.
So, the new slogan: Altcoins with Gravity Well are also obsolete on launch. You need something like Temporal Retargeting or DigiShield.