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8.5 BLOCKCHAIN CHALLENGES AND SOLUTIONS FOR HEALTHCARE 219

Database 1

Application
back-end
Database 2

Application
back-end Blockchain

FIG. 8.16
Off-chain blockchain architecture.

8.5.1.3 Off-chain blockchain advantages
The aforementioned approach complies with GDPR because the proposed approach can completely
delete personal data. Similarly, since the hash of the data is stored on-chain, data security is also
preserved.

8.5.1.4 Off-chain blockchain disadvantages
The major disadvantage of the aforementioned system is that anybody linked with that particular local
data can access the data without the consensus from other nodes. Data owners’ rights are compromised
by this. The local database is open to more attack vectors. Finally, managing the hash with API adds
management level complexity.
Finally, the GDPR versus blockchain is still a paradox. There are still a few questions on the off
chain data storing mechanism. They are:

• Who is the owner of the off-chained data?
• Is it possible to encrypt the off-chain data?
• Is data access controllable or not?
• What if off-chain data is copied illegally?

We will now explore several blockchain technology solutions available for healthcare big data.
Blockchain health: “Blockchain Health” is a US based healthcare data handling software com-
pany. By using their service, “Pokitdoc” developed by Smith [77], patients and researchers can share
information. They use their “DoKchain” based on-chain and off-chain data storing infrastructure.
There are a set of key-pairs for each node for identity verification. Proof of Elapsed Time (PoET)