Da alcuni giorni sul sito di genesis mining non è più possibile acquistare contratti di mining bitcoin front end, nè di tipo X11. Attualmente ci sono solo 2 tipi di possibilità sottoscrivibili, entrambe di durata biennale, ossia: ethereum e monero. Per minare ethereum viene utilizzata la tecnologia "Dagger-Hashimoto". Per chi volesse entrare nei dettagli di questa modalità di mining riporto di seguito un documento in lingua inglese.
Dagger Hashimoto is a proposed spec for the mining algorithm for Ethereum 1.0. Dagger Hashimoto aims to simultaneously satisfy two goals:
1) ASIC-resistance: the benefit from creating specialized hardware for the algorithm should be as small as possible, ideally to the point that even in an economy where ASICs have been developed the speedup is sufficiently small that it is still marginally profitable for users on ordinary computers to mine with spare CPU power.
2) Light client verifiability: a block should be relatively efficiently verifiable by a light client.
With an additional modification, we also specify how to fulfill a third goal if desired, but at the cost of additional complexity:
Full chain storage: mining should require storage of the complete blockchain state (due to the irregular structure of the Ethereum state trie, we anticipate that some pruning will be possible, particularly of some often-used contracts, but we want to minimize this).
Dagger Hashimoto builds on two key pieces of previous work:
Hashimoto, an algorithm by Thaddeus Dryja which intends to achieve ASIC resistance by being IO-bound, ie. making memory reads the limiting factor in the mining process. The theory is that RAM is in principle inherently a much more generic ingredient than computation, and billions of dollars of research already go into optimizing it for different use cases which often involve near-random access patterns (hence "random access memory"); hence, existing RAM is likely to be moderately close to optimal for evaluating the algorithm. Hashimoto uses the blockchain as a source of data, simultaneously satisfying (1) and (3) above.
Dagger, an algorithm by Vitalik Buterin which uses directed acyclic graphs to simultaneously achieve memory-hard computation but memory-easy validation. The core principle is that each individual nonce only requires a small portion of a large total data tree, and recomputing the subtree for each nonce is prohibitive for mining - hence the need to store the tree - but okay for a single nonce's worth of verification. Dagger was meant to be an alternative to existing memory-hard algorithms like Scrypt, which are memory-hard but are also very hard to verify when their memory-hardness is increased to genuinely secure levels. However, Dagger was proven to be vulnerable to shared memory hardware acceleration by Sergio Lerner and was then dropped in favor of other avenues of research.
Approaches that were tried between Dagger and Dagger Hashimoto but are currently not our primary focus include:
"Blockchain-based proof of work" - a proof of work function that involves running contracts taken from the blockchain. The approach was abandoned because it was long-range attack vulnerabilities, since attackers can create forks and populate them with contracts that they have a secret fast "trapdoor" execution mechanism for.
"Random circuit" - a proof of work function developed largely by Vlad Zamfir that involves generating a new program every 1000 nonces - essentially, choosing a new hash function each time, faster than even FPGAs can reconfigure. The approach was temporarily put aside because it was difficult to see what mechanism one can use to generate random programs that would be general enough so that specialization gains would be low; however, we see no fundamental reasons why the concept cannot be made to work.
The difference between Dagger Hashimoto and Hashimoto is that, instead of using the blockchain as a data source, Dagger Hashimoto uses a custom-generated 1 GB data set, which updates based on block data every N blocks. The data set is generated using the Dagger algorithm, allowing for the efficient calculation of a subset specific to every nonce for the light client verification algorithm. The difference between Dagger Hashimoto and Dagger is that, unlike in the original Dagger, the dataset used to query the block is semi-permanent, only being updated at occasional intervals (eg. once per week). This means that the portion of the effort that goes toward generating the dataset is close to zero, so Sergio Lerner's arguments regarding shared memory speedups become negligible.
