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Chapter 4 A critical review on using blockchain technology in education domain 97

(b) Simplified Byzantine fault tolerance (SBFT): SBFT uses a per-
missioned BC composed of three entitiesda single generator,
multiple signers, and network (chain core) nodes. In SBFT, a
node called as block generator collects batches and validates
(based on rules) the proposed transactions into a new block.
Multiple nodes designated as block signers ratify/verify the
proposed block with their signatures. Other nodes accept
the blocks only if signed by majority of block signers. This
approach prevents double spending by distributing and
verifying the functionalities. Maintaining a single generator
simplifies synchronization problem and also increases the
speed of block generation. This approach is scalable but
compromises on transparency in public BCs as only authen-
ticated entities participate. It also improves on the security
and privacy of transactions by hiding components of transac-
tion while maintaining integrity, encrypting block metadata
information, and using one-time addresses for the nodes.
This approach is used in Chain.
(c) Delegated Byzantine fault tolerance (dBFT): The dBFT follows
same rules as PBFT. Various nodes in the network communi-
cate through speakers. These nodes elect generals who act as
delegates. Hence, in dBFT, some of the nodes are chosen as
delegates of the other nodes. These delegates pursue the
consensus protocol similar to PBFT. Atleast two-thirds of
the delegates should validate/agree for the consensus.
Election of delegates prevents fraudulent generals. Speaker’s
verdict can also be verified by the delegates as the decision
of the nodes is stored. Thus, dBFT overcomes the problems
of dishonest delegates and speakers in BFT. The NEO
(formerly Antshares) is one of the types of cryptocurrency
used in DBFT. This method holds all the properties of PBFT.
(d) Federated Byzantine agreement: The main issue in BFT is that
two-thirds of the nodes (leaders) should agree to reach an
agreement. This is overcome in federated Byzantine fault
tolerance (FBFT) where a set of nodes called as quorum is
selected by set of nodes for the entire system. A trustworthy
quorum slice (subset of nodes in quorum) is chosen by a
single node. The main advantages of FBFT include decentral-
ized control, selection of trustworthy validators (quorum
slices) by the individual nodes, and resilience to failures. It
can be used in permissionless BCs unlike other BFT
approaches that are either private or consortium based.
This approach is used by Ripple and Stellar.