IEEE Electrification - December 2020 - 84

asymmetric cryptography representing pairs of public and
private keys in a blockchain ensures the message's
authentication and privacy. Each participant applies public
and private keys to encrypt and decrypt the data in the
blockchain network. Both keys are a digital signature that
is specific to a participant and provided before the participant submits any data to the blockchain; however, they
have different functions. The public key, which is accessible by other participants, is a publishable identifier that
allows each participant to be addressable in the blockchain network. The private key is kept secret.
Figure 6(a) and (b) depicts public and private keys for
authentication and privacy, respectively. As for privacy, if
participant 1 wants to send an encrypted message to participant 2 and does not want to reveal this message to the
other participants, then participant 1 will use participant
2's public key to encrypt the message, representing a
string of random numbers and letters. The encrypted
message is sent to participant 2. After receiving the
encrypted message, participant 2 decrypts the message
using his or her private key. Privacy is, hence, guaranteed
because the participants cannot decrypt and read the
message without participant 2's private key. As for
authentication, assume that participant 1 sends a

message to participant 2 and wants to make sure that participant 2 knows this message is from participant 1. Participant 1 will encrypt this message into a string of random
words and letters using his or her private key. Participant 2
receives the message and will use participant 1's public
key to decrypt it. If the public and private keys do not
match, participant 2 can see only a string of random
words and letters. Therefore, authentication is maintained
because nobody can impersonate participant 1 without
participant 1's own private key to send messages to the
other participants.

Blockchain Structure

A blockchain is a chain of data blocks, the structure of
which is shown in Figure 7. Each data block for the blockchain data storage consists of two parts: the block header
and the block body. In the block body, the data stored in
the form of a Merkle tree will not be revealed because they
are encrypted as fixed-length strings by using the hash
function. The hash value of a Merkle root, which aggregates all of the encrypted data of a Merkle tree, is stored in
the block header so that the data block can be tracked by
referring to the Merkle root of the block header. Also, the
block header stores the hash value of the Merkle root from
the last block, which links all of the
data blocks to form a chronologically ordered chain. Once the data
Merkle Root
block is added to the blockchain,
Hash G
any attempt to change the data in
one data block will also change the
hash value in the corresponding
Hash E
Hash F
block header. Therefore, the blockchain structure is tamper proof
because any attacks on the data
Hash A
Hash B
Hash C
Hash D
block will be recognized immediately since the hash value of the
Hash
Function
revised block will not match the
Transaction A
Transaction B
Transaction C
Transaction D
hash stored in the next data block.
In the blockchain network, every
participant holding a blockchain
Figure 5. The structure of a Merkle tree.
would ensure that its blockchain is
the same as those of other participants. A participant who stores
Participant 2's
Participant 2's
data in the blockchain would forPublic Key
Private Key
mulate them as data blocks and
propagate them to other participants randomly for validation. The
Participant 1
Participant 2
updated blockchain, which is vali(a)
dated based on preset rules, will be
Participant 1's
Participant 1's
added to the participant's own
Private Key
Public Key
blockchains, and the data blocks
are propagated randomly to other
participants for validation. Once all
Participant 1
Participant 2
blockchain network participants
(b)
have verified the data blocks, the
Figure 6. An example of public and private keys. (a) Privacy. (b) Authentication.
blockchain is updated.

84

I E E E E l e c t r i f i cati o n M agaz ine / DECEMBER 2020
IEEE Electrification - December 2020

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