Page 119 - Handbook of Deep Learning in Biomedical Engineering Techniques and Applications

Chapter 4 A critical review on using blockchain technology in education domain 107

sending excess amount in a wallet to a second wallet
isolated from the Internet can be used.
(f) Peer-to-peer networkebased attacks: These threats occur in
BC network layer. Hackers exploit network vulnerabilities to
enforce the following attacks:
• Routing attack: Here the hacker tampers with the transac-
tions before pushing them to the peer nodes. The hacker
partitions the network and creates a delay attack by
tampering with the messages before sending them to the
network.
• Eclipse attack: When a node “A” selects “n” malicious
peers (X1, X2, .Xn) to have a copy of distributed ledger,
then the attacker can eclipse the view of the original ledger
and present a manipulated ledger. To overcome eclipse
attacks, trust factor of nodes are to be considered. Mali-
cious nodes are to be detected and eliminated.
• Sybil attack: Here the attacker floods the network with a
large number of nodes with pseudonymous identity. The
major objective is to generate a fork enabling double
spending for the attacker. Block generation capability
depends on computational power of the miner. This rela-
tionship can provide Sybil attack resistence.
• DDoS attack: When a network is flooded with a large num-
ber of requests from different IPs, the system becomes over-
loaded. Upto some extent, this attack can be prevented in
BC using transaction fees. DDoS attacks can be detected us-
ing attack patterns and machine learning techniques. PoA
also overcomes DDoS attacks to a certain extent.
• Transaction malleability attack: When an attacker mod-
ifies the transaction ID, then its hash can be changed.
Hence, this transaction can be verified before the original
transaction and result in payment. Silk road attack uses
“transaction malleability” to repeatedly withdraw coins
from the bitcoin system until it was completely empty.
• Timejack attack: Internal timing of a node in a BC network
is got from the median time of its peer nodes. When an
eclipse attack occurs, median time of the node depends
on timing of the malicious nodes only. Now the node
cannot accept blocks from original BC network. Double
spending can now occur.
• DNS hijacks: Here the attacker is able to intercept DNS
queries and redirects it to a malevolent node. This can
occur due to man-in-the-middle attack, cache poisoning,
router hijacking, or using a rogue DNS server.