Page 117 - Handbook of Deep Learning in Biomedical Engineering Techniques and Applications

Chapter 4 A critical review on using blockchain technology in education domain 105

• Perform transaction by spending their coins in their
privately mined chain.
• Create a private chain by not broadcasting the blocks to
the BC network
(c) Smart contractebased attacks: If smart contracts have bugs,
then attacks can be launched. DAO attack is smart contract
based. Crowd funding of decentralized autonomous organiza-
tion was attacked. Here the attacker contributes a small amount
and without checking settlement of amount uses a recursive
withdraw function. Hard forks can overcome this attack.
a. The possibility of delegating control to untrusted functions
from other smart contracts results in reentrancy attack.
This has occurred in solidity. Developers should also
strengthen their smart contracts against overflow/under-
flow errors.
b. Ethereum Virtual Machine executes smart contracts. This
can result due to bugs in immutable smart contracts as
in DAO attack. Ethers can also be transferred to an
orphaned address without an owner. Ethereum address
can be modified with padding’s that enables the hackers
to send victim’s ethers to their address. This results in
short address attack as in Coindash. Some of the common
attacks include reentrancy, overflow, replay, short address,
cryptojacking and balance attacks. Cardano and Zilliqa are
more secure against these attacks.
(d) Mining pool threats:A group of miners can share their re-
sources for mining. Some of the attacks include the following:
• Selfish mining attack: A selfish miner builds blocks secretly
on top of the existing BC. When he has more blocks then the
current longest chain, a private fork can be published by the
selfish miner as the new longest chain. Double spending
attack can be done by the miner to reverse his previous
spending before publishing the longest chain. This is also
called as block withholding attack.
• Block with holding (BWH): Here, adversary miner never
publishes the block to the chain. To prevent BWH, only
trusted miners should be present in the network to prevent
rogue miners.
• Parasite chain attack: This is very similar to selfish mining
attack. Here the attacker secretly builds a subchain of
blocks. He then performs a transaction1 on the main
chain. The secret subchain has a conflicting transaction2