14762

13288

كارشناسي ارشد

مخابرات سيستم

اصفهان : دانشگاه صنعتي اصفهان

1398

دوازده، 94ص. : مصور، جدول، نمودار

محمد دخيل عليان، محمدحسين منشئي

علي فانيان، حامد نريماني

1398/04/25

كتابنامه

مهتدسي برق

مهندسي برق و كامپيوتر

1398/04/25

2546604

Sybil Attack Modelling and Analysis in Shard Based Blockchains Tayebeh Rajabi t rajabi@ec iut ac ir Jun 12 2019 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisors Assoc prof Sayed Mohammad Dakhilalian mdalian@cc iut ac ir Assoc prof Mohammad Hossein Manshaie manshaei@cc iut ac ir Abstract A new way was beginning to extend and improve distributed networks by introducing Bitcoin and Blockchain Securityand scalability are the most important issues for change centralized networks to distributed networks with Blockchain TheNakamoto s Blockchain is secure but it is not scalable because it needs too much computational power so this is not useful indifferent usage Finally scientists propose Sharding as the best solution for scalability of the Blockchain Elastico wasthe first Shard based Blockchain and some other protocols were proposed to improve its operation All of these protocolsare weak against the Sybil attack In this attack the attacker tries to impersonate and make a lot of fake ids to increase hisinfluence and his vote in the network So he can annul consensus in some shards or he can change the output of some shardsand puts his favorite transactions in the Blockchain In this thesis we talk about Shard baseed protocols in details then we analyzed one of these protocols Elastico aboutsecurity against Sybil attack we found that the PoW that used to ID generation in the initial phases of this protocol isvulnerable against Sybil attack and the node with high hash power can generate many fake IDs He can control the shardwhen his IDs entered the shard In the following we have expressed the attack conditions and the goals that the attacker maybe following Then we obtained some equations to calculation the attacker s success probability in the Sybil attack Afterthat we simulated the initial phases of the Elastico and simulated this attack in that According to our observations wecan say the node that has 25 hash power of the entire network who can generate 25 of the total IDs of the network candoing the attack with success probability about 0 2 So the PoW is not a suitable way for ID generation in the Shard basedprotocols Key Words Blockchain Sharding Proof of Work Sybil Attack Success Probability

محمد دخيل عليان، محمدحسين منشئي

علي فانيان، حامد نريماني