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Chapter 4 A critical review on using blockchain technology in education domain 95

(m) Proof of elapsed time (PoET): This protocol works in a private/
consortium BC where the nodes participating in the network
are authenticated. Such trusted nodes wait for a random time
interval. Once this time interval is elapsed, they can perform
the mining process. Once the job is complete, the miner
receives a certificate. The system also monitors for compro-
mises by checking the number of times a particular node is
able to participate in the mining process. This protocol re-
quires a software to monitor the entire process and is more
energy efficient than PoS. Intel SGX system is based on PoET.
(n) Proof of activity: This approach combines the advantages of
PoW and PoS. In the PoW, the miners will try to solve the
hash function. However, the solved block will only contain
a header, and miners address without any transaction. The
transactions are added to the block, and according to the
solved blocks, header points to suitable validators. A group
of validators are chosen to sign the new block to reach
consensus based on the stake they possess. This step is
done by using PoS. Both miners and validators are paid for
their mining job. This mechanism secures against attack,
and it is also not power hungry. Decred and Espers BCs
make use of this approach. Since mining and validation
requires equal participation of all nodes, the probability of
51% attack is reduced to zero.
(o) Proof of history: Consider that a transaction has occurred
before/after a historic event. Repeated hashing is performed,
and counter and hash values are recorded. Output of one
SHA256 stage forms input for next stage of hashing. Solana
uses this approach.
(p) Proof of retrievability (PoR): A file system acts as a prover who
tries to prove the client verifier that a target file can be fully
recovered. PoR has less communication overhead than
transmitting the entire file. It can be useful in remote storage
systems in cloud environment. This approach is used in
Microsoft.
(q) Proof of burn: Proof of burn is based on the burning coins
where miners send their coins to an irretrievable address.
The miners get priority to solve the next block according to
the amount of coins that they have burnt. Burning creates
more stability as long-time miners tend to hold their coins
(not looking into short-term benefits), making them more
suitable for mining. It also makes the network more distrib-
uted. The main disadvantage is that there is wastage of coins.
Coins once burnt cannot be recovered. Slimcoin uses this
consensus method.