just want to know the classic proof of stake consensus has a lot of problem
how do you solve it in Qtum ?
thank you
"
POS Attack Vectors
the main attack vectors to the consensus approaches analyzed later in this section are summarized. In general, Denial of Service (DoS) and Sybil attacks against these approaches (performed at the network and/or consensus protocol levels) are possible. A DoS attack is an explicit attempt to disrupt the normal operation of the blockchain network by sending lots of data to its nodes (for example, by sending many transactions of low value so the system cannot process normal transactions). In a Sybil attack the normal operation of the network is subverted by a malicious adversary that creates and controls a many misbehaving nodes (which could appear as belonging to different participants).
Miners' default behaviour in PoW consensus is to immediately announce to the network each new found block. In selfish mining attacks, a misbehaving miner attempts to waste computational resources of other miners, as follows. When the malicious miner finds a valid block he temporarily withholds it and continues mining on top of it, trying to find more blocks before the other miners even find one; and when another miner finds a valid block, the attacker announces the blocks he was withholding. Even if for some researches , this attack vector could be in practice very unlikely, as mentioned in section IV.D, there are cases where miners could be motivated to carry out a slight variant of this attack, where valid blocks are selectively discarded in order to modify the result of a stochastic procedure in which there is much at stake.
In a short-range attack the attacker, controlling certain percentage of the resources used to secure the system (e.g., computational resources or cryptocurrency stake) performs a transaction (e.g., to spend coins or to execute a step of a contract) and then tries to reverse it (e.g., to make a double-spending, that is, successfully spending some of the cryptocurrency coins more than once) as follows. After the attacker submits to the network the transaction he aims to revert, he starts mining a blockchain fork (from the previous block) in which that transaction is not included, without publishing it until that transaction has at least a certain number n of confirmations. If by then the attacker achieved to mine (mint) more than n blocks in his blockchain fork, he publishes it, and being this the longest chain it is accepted as the new valid blockchain by the network; therefore, the transaction in question is reversed.
In a long-range attack the attacker (controlling a certain percentage of the resources used to secure the system) starts mining a blockchain fork from many blocks back or even from the very first (genesis) block; aiming to obtain block rewards and/or to reverse a transaction. This attack would be possible in systems based on PoS consensus, given that although the attacker may only own a small percentage of all coins (at the point of the fork), in his blockchain fork he is able to move his coins freely, which allows him to solve the computational puzzle to mint blocks much more easily, and therefore, to rapidly build a longer blockchain.
A coin-age accumulation attack could be possible in approaches based on PoS where the coin-age is used to compute a measure of nodes' stakes, the total
consumed coin-age determines the valid blockchain, and the coin-age of an unspent transaction output (UTXO) is computed as its value multiplied by the number of blocks elapsed since it was created (e.g., Peercoin as will be seen later in this section). In this case, the attacker would split the coins he owns (a high enough percentage of all coins) into multiple UTXOs and wait until his stake becomes several times the average. Then, after that, the attacker would be able to mint several blocks in a row with a high probability, allowing him to fork the blockchain and reverse transactions (e.g., to make a double-spending).
In PoS consensus the solution to the puzzle necessary to mint a given block depends on the previous block's hash. Then, an attacker (with enough computation resources and stake) minting at height h of the blockchain could try to influence the hash of the current block (by selectively modifying its set of transactions) in a trial and error process until he is able to mint the block at height h+1. This is known as a pre-computation-attack and it could be done recursively in order to build several blocks in a row, to obtain the corresponding block rewards and/or perform a double-spend attack.
"
also Ethereum seems will not switch to fully POS until 2018 or 2019 ?
and their Casper is not ready yet,
why Qtum choose POS from the very beginning?
thank you!
proof of stake still have some potential attack vectors.
?
