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• Distributed: A blockchain can be scattered and can Despite centralizing the blockchain's overall membership,
change the number of nodes in a blockchain to increase it's ideal for small networks and test nets [19].
flexibility and reduce the chances of a successful attack. As
Blockchain is a chain of timestamped blocks linked by C. The types of Blockchain Technology
cryptographic hashes, as the name suggests [16]. The two most frequent types of blockchain [20] are public
and private.
A. Hash function 1-Public blockchain, which means that all network users
can observe transactions, but the identities of the nodes who
Using preimage as the input and Image as the result, a initiate them are hidden [1]. It's a decentralized peer-to-peer
hash function turns a variable-length input into a network that's not controlled by a single entity [21]. In Fig. 3
fixed-length output. A hash function is a one-way function, describes the Public Blockchain [22].
which means that identifying its original Image by Image is
impossible. The following are the characteristics of the Fig 3. Public Blockchain Network for IoT [22].
perfect hash function [17]: 2- Private blockchain: A permissioned blockchain [20, 23]
sets a list of rights that players with specified characteristics
1) Accept any preimage length. must have to operate within the network. The block creation
is controlled by a single entity that owns this kind.
2) For identical preimages, the calculated Image is identical. Organizations typically utilize a private blockchain to record
transactions or distribute data to a small group of users [1]. In
3) The length of any preimage Image is fixed, and it can be fig.4 describe the Private Blockchain [22].
computed quickly.
Fig 4. Private Blockchain Network for IoT [22].
4) Exhaustion is the only method to discover the preimage 3-Consortium Blockchain: It is a semi-decentralized kind
through the Image. in which the blockchain network is managed by multiple
organizations. It differs from the private blockchain, which
5) Finding another preimage that corresponds to the is controlled by a single entity. More than one entity operates
estimated Image of a particular preimage is tricky. as the authority to do mining or exchange information in this
type of blockchain. Blockchains are employed in a variety of
6) There is no connection between the photographs before industries, including banking and government agencies [24].
and after the change; even minor changes in the preimage In fig.5 describe the Consortium Blockchain [22].
cause big changes in the image.
Fig 5. Consortium Blockchain Network for IoT [22].
B. Algorithm of Consensus

On the blockchain, consensus methods ensure that each
new block added to the network is the only version of the
truth. All nodes in a distributed/decentralized computer
network agree. Consensus algorithms are critical for
blockchain networks because they ensure the integrity and
security of these distributed computing platforms [3]. There
are many important consensus algorithm in blockchain:

Proof of Work (PoW): It was the first method utilized to
reach a worldwide consensus[18]. Within Blockchain
architectures, The PoW has traditionally been the most
popular means of achieving a consensus. By seeking for hash
functions with a difficulty proportional to the network's
processing power, PoW makes it challenging to construct a
legal block and link it to a Blockchain. You must revalidate
any future blocks after changing a block. The older the block
being updated is, the more validations are necessary When
only a few miners or groups of miners are capable of
generating new blocks every ten minutes, even a newly
validated block update is costly[3].

Proof of Stake (PoS): After criticism of PoW, an
alternative technique called proof of stake was devised (PoS).
PoS substitutes a random selection process for computing
activity, with the probability of successful mining
proportional to the number of validators. The stake nodes'
investment in the system, i.e., coin ownership, affects the
chance of generating a block.

Proof-of-Authority(PoA): In response to the risks
involved with Proof-of-Work, it was first proposed as an
addition to the Ethereum blockchain for checking internet
usage. The core tenet of Proof-of-Authority is that only
selected, trusted nodes are allowed to create new blocks.