2 Background 2 1 BitTorrent Protocol BT is a P2P protocol for large scale content distribution over the Internet 7 In a BitTorrent network the data will be separated to several segments in a non-sequential manner in information propagation 7 Each peer can get segments of the data from other peers and concatenates them in an integrated file Also each peer in the network will provides other peers data segments in its local storage There are two types of peers in a BitTorrent network one is leeches the other is seeds Technically leeches are the clients seeds are the original distribution server Leeches can download resources from seeds and also can upload the segments of resources they have Seeds can only upload their resources to the clients leeches 7 A modified BitTorrent protocol can be used in P2P multimedia streaming network 7 2 2 Bitcoin Network and Block chain Technologies Bitcoin network is a P2P electronic cash system 3 Bitcoin is the first truly decentralized global currency system 8 Like a traditional cash system Bitcoin system also has ledger to record the transactions But not like a traditional cash system that the ledger is in the control of the authority ex a bank in Bitcoin system each user has their own copy of the ledger 3
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8 The media of the ledgers in Bitcoin network is called blockchain 3 Blockchain is the backbone of the Bitcoin system Peer to Peer Network Applications and Issues 9 There is a special type of nodes called miners In Bitcoin network miners will contribute their computing power ex CPU GPU power to solve the proof of work 3 The proof of work is like a puzzle once the miner solved it there will be a new block discovered 3 The new block will be appended to the end of the blockchain in this miner s Bitcoin wallet as an award The new block will also be broadcasted to the whole Bitcoin network As a result all the ledgers in Bitcoin user s wallet should be increased by one block The Bitcoin network is extremely simple peers work all at once but they do not need to be identified since once the block is found it will be broadcasted to the whole network 8 3 Discussion 3 1 DDoS Attack in BitTorrent Network The power of all the nodes hosts in a P2P network could be enormous As long as there are enough users hosts in this network all the users will enjoy a high speed downloading experience But because all the peers hosts are exposed in the network it gives attacker a chance to attack a specific computer in the network 4 In BitTorrent network the directory server is actually a tracker the duty of the tracker is to tell those peers who want to get a resource from the network which peers have the resource
Attackers can hack the tracker server and tell other peers that a peer victim in this network has the resources they want but it could be not true However other peers do not know the truth the Peer to Peer Network Applications and Issues 10 tracker is hacked they will try to start a connection with the victim s computer Suppose a huge number of computers have a full TCP connection with one computer victim all at once the victim s bandwidth will be exhausted The result is that the victim will suffer a network jam 5 6 or even experience a system dead halt If the victim is a company or organization the loss caused by DDoS attack will be huge 4 This type of attack is not unsolvable By improving the tracker protocol can effectively prevent DDoS attack, In addition, a client need to install the latest firewall on their device to prevent many common DDoS attacks To home users if they discovered they lose Internet connection they can reboot their router to obtain a new dynamically allocated IP address 3 2Decentralized Bitcoin Network and 51 Attack Suppose Mike and Tom use Bitcoin to complete the deal of a cup of coffee
Normally the deal is immediately put into a trading pool waiting for the miners to add itself to a new block and start working on it Assuming that Mike is the big boss and has 51 percent or close to or above 50 percent of the power of the network he really doesn t want to pay for the coffee so he attacks Mike can discover a new block faster than the other peers miners and add to its ledger but he can choose now to broadcast it to the Bitcoin network now and start to find the next block This will cause a problem called blockchain fork 8 According to the Bitcoin protocol the Bitcoin network will only accept the longest chain Thus once Mike broadcasts his longer chain the other fork chains orphan chains will be discarded by the network, As a result, Tom will never get the money because the transaction is discarded with the orphan chain but the coffee is gone Peer to Peer Network Applications and Issues 11 Because the root cause of this problem is due to the Bitcoin protocol there is no better way to eradicate this kind of attack However as long as there are enough miners in this network and most of them are honest miners the network will be robust and safe
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