Trovare ingiusta la distribuzione iniziale di Nxt è stata una reazione più emotiva che razionale, e il passare del tempo lo sta dimostrando. Comunque Nem resta un buon progetto. Riguardo al Proof-of-Importance ho trovato questa bozza online che ora è stata cancellata, ho salvato il testo seguente.
Proof of Importance: A Fairer Way to Secure P2P CurrenciesIntroduction
Proof of Importance (PoI) is a novel method for security distributed peer-to-peer (P2P) currencies, using the structure of the transaction graph to determine nodes that are structurally important to the overall network. PoI is closely related to Proof of Stake (PoS), where holding units of currency for a period of time gives a person a higher "stake" in the network. Actors with a higher stake in the network are considered more trustworthy.
Proof of StakeIn PoS, an actor has a stake in the network that is measured in "coin-days," which is a metric based on the number of units of the currency (coins), which is then weighted by the time since the last transaction the coins were in (days). To prevent people from quickly sending coins around to many accounts to boost their stake in the network, the coins a person holds are usually weighted at 0 for the first 24 hours after being used in a transaction.
Proof of ImportanceWhile PoS can work to secure a network, it also promotes hoarding of the currency and discourages actually using the currency in transactions. It also has the effect that the "rich get richer," because accounts with large numbers of coin-days are more likely to receive transaction fees from the network. For the crypto-currency project NEM (New Economy Movement; No-Envy Movement), a more equitable way of distributing transaction fees and promoting the use of the currency, while securing the network, was desired.
Intuitively, PoI is a measure of how important an account is to the health of the network as a whole. An important account is used in many transactions and also has a large number of coin-days.
With PoS implemented without transparent forging, governments could control a currency simply by buying a majority stake and holding on to it. PoI makes this impossible by being based not only on the share of the currency that an account has, but also by transactions carried out with other accounts.
For the first version of PoI, it is proposed to use a modified form of PageRank to calculate the importance of nodes in a network. In a P2P currency, accounts can be considered nodes and transactions between accounts can be considered edges linking the nodes.
PageRank is an algorithm for calculating the stationary probability distribution of an ergodic Markov chain. It was developed originally for ranking web pages in Google search results, but has also been successfully applied to word-sense disambiguation, citation analysis, and ranking popular locations in a spatial environment.
In PageRank, the importance of a node in a graph is related to the importance of nodes that point to it. Thus the algorithm uses direction information about which nodes point to each other. In the context of cryptographic currencies, nodes are accounts specified by public and private keys, and the edges connecting nodes are transactions that transfer currency. In iterative implementations of PageRank, all nodes are first initialized with the probability that a node is randomly chosen,
For PoI, rather than initializing all nodes with the random probability of being chosen, the value of each account in coin-days is used initially.
Since PageRank requires a directed graph, if two nodes transfer currency between each other, the direction of the edge between the nodes is based on the direction of net flow of currency; if the if there is not net flow of currency, that is, the two nodes trade the same amount between each other, then no edge is added linking the nodes. This helps forging to be more equitable, because under standard PoS, an account for an exchange could just keep all the currency in one account and gain significant stake in the network. Using PoI, when people withdraw from an exchange, they could get a boost in their own PageRank because a node with lots of coin-days will transact to them.
If nodes in a graph are traversed in a pre-determined order, then the results of this algorithm are deterministic. This determinism can allow transparent forging, because any node could calculate the importance of other nodes based on transactions in the block chain.
Specific to NEM, the following points should be considered:
- Messages sent between accounts using NEM's secure messaging service will not be considered as linking two nodes. If message passing was included, it could make it too easy to manipulate the connectivity of the network.
- Accounts with less than 1000 NEM will not be considered as nodes in the network. Otherwise someone could cheaply create many accounts and manipulate network connectivity that way.
- Since Proof of Importance is based not only the amount of coin-days held by one account, but also the graph-theoretic imporantance of the node in the network, carrying out attacks on the network is prohibitively expensive because many important nodes would have to be created and point to each other.
