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Chapter 4 A critical review on using blockchain technology in education domain 91

3. Consensus

Since BC is a P2P network, decisions have to be made based on
majority voting by the peer members before adding a new block
to the network. Such a collaborative and decentralized decision-
making leads to a win situation for the entire network. Thus in a
consensus protocol, individuals of the group construct and
support the decision that works best for the group. Consensus
protocol [9] ensures the group interest in collaborative and coop-
erative decision-making process. It also ensures equal participa-
tion and responsibility from all members of the group through
validation and verification phases. Such protocols are broadly
classified as proof-based, vote-based, and graph-based protocols.
This section briefs on commonly used consensus protocols.

3.1 Proof approaches
Proof protocols are based on concepts to be proved. The
following are some of the commonly available proof-based
consensus protocols [11].
(a) Proof of work (PoW): PoW is performed by the miners
competing to solve a cryptographic hash problem.Other diffi-
cult problems include integer factorization, determining output
without input. Attributes such as block number, hash of the
previous block, and data values of the current block are known
while nonce is unknown. SHA256 algorithm is used to generate
the hash value by randomly substituting the nonce along with
all the other known attributes. A target hash value is fixed. If the
generated hash value is less than the target hash and is with
required difficulty, then the nonce is found and is stored in
the block along with the hash. The difficulty level assures that
a required number of zeros occur at the beginning of the block
hash. The miner who finds this hash value first will be the
winner and will add the new block to the BC. PoW weaves
game theory into a distributed protocol and applies incentives
to miners at possible actions. It is optimization free as hashing
function cannot be evaded in the mining protocol. It is approx-
imation free as hash function generated should satisfy the
constraints. Only then the block is successfully generated.
Bitcoin and Litecoin are based on PoW.
The cryptographic problem is difficult to solve for the miner
but easy to verify in the network. The miner who solves the prob-
lem first gets the reward. This reward decreases over time, and
the complexity of problem increases and is resource intensive.
Due to the computational complexity, PoW offers distributed