Blockchain in WSNs, VANets, IoTs and
Healthcare: A Survey
Fatima Tariq, Nadeem Javaid, Maria Anwar, Abdul Rehman Janjua, Muhammad
Haseeb Khan and Asad Ullah Khan
Abstract Recently, blockchain technology has become one of the most ground-
breaking technology. Blockchain was introduced to support digital transactions and,
provide access to the distributed ledger in a secure and trusted way. Blockchain with
smart contracts has the ability to provide secure transaction among users without the
need of trusted third party or intermediary. In this paper, we presented a compre-
hensive survey on blockchain applications for Wireless Sensor Networks (WSNs),
Vehicular Adhoc Networks (VANets), Internet of Things (IoTs) and healthcare. We
review the problems addressed, their proposed solutions and, experimental evalua-
tion security analysis. We also spot and review future challenges or open research
issues of utilizing blockchain for WSNs, VANETs, IoTs, and healthcare.
Blockchain is considered as one of the most hyped and disruptive innovations nowa-
days and can be used to solve the problem of double spending attack and to maintain
the order of transactions. It continues to develop in such a way that will modern-
ize the way we interact, trace, and track payments among participants. Blockchain
was ﬁrst introduced for digital transactions with bitcoins, and now it is adopted
by various cryptocurrencies . The transactions are grouped into size-constrained
structure labeled as blocks, with the similar timestamp. Miners are responsible for
achieving consensus and link the blocks with each other in chronological order, and
every block encompasses the hash of the preceding block to make the blockchain.
Depending on the type of blockchain, different consensus algorithms are used. PoW
is very well-known algorithm and solves complicated computational problems like
ﬁnding hashes to guarantee authenticity and veriﬁability. As an alternative of divid-
Fatima Tariq, Nadeem Javaid (Corresponding Author), Maria Anwar, Abdul Rehman Janjua,
Muhammad Haseeb Khan and Asad Ullah Khan
COMSATS University Islamabad, email: firstname.lastname@example.org
2 Fatima et al.
ing blocks evenly to the mining power of miners, Proof of Stake (PoS) is used to
divide blocks evenly to the current wealth of miners. PoS allows just selection of
blocks and avoids the well-off member to lead the network of blockchain. Several
applications of blockchain are shifting towards PoS because it provides enhanced
scalability and prominent decrease in computation power. Other consensus algo-
rithms include Proof of Concept (PoC), Byzantine Fault Tolerance (BFT) and its
The blockchain technology provides transparency, trustless, but secure transac-
tions in the decentralized network, which helps in attaining robust and auditable
records of all transactions. Hence, blockchain is applied to different scenarios for
Wireless Sensor Networks (WSNs), Vehicular Adhoc Networks (VANets), Inter-
net of Things (IoTs) [3, 4, 5], smart grids  and healthcare. In these scenarios,
blockchain is used with smart contracts, which are lines of code of protocol and exe-
cute the terms and conditions of the contract between two parties . Smart contract
helps in translation of contractual clauses into embeddable code, which minimizes
the need for trusted third party and transaction are truly between two parties. In
general, smart contract is an agreement between two parties who do not trust each
other, so contractual clauses are automatically imposed.
Blockchain in WSNs is a big challenge, as sensor nodes have limited volume
of batteries which results in limited number of operations, so the whole network is
limited. The dependence of energy consumption depends on the amount of trans-
mitted, received and processed information, data acquisition from sensor nodes and
some other factors. The use of Proof of Work (PoW) is also a big task, as PoW is a
resource and energy intensive task. Same is the case with IoT devices . Managing
vast number of IoT devices is a technical challenge. So, blockchain was adopted to
develop a distribuited environment in WSNs and IoTs. As mechanical vehicles are
evolving into fully automated vehicles. The current security mechanisms provided
by researchers are not up to date. In vehicular networks blockchain can be used to
provide authentication, trust and security between vehicle to vehicle and vehicle to
infrastructure communication .
In healthcare industry, patient’s data is the most critical and sensitive information.
Patients’ medical record is mostly scattered around different hospitals and systems
owned by healthcare industry. Digitalization has the ability to store the medical
record of patient digitally, which is known as Electronic Medical Record (EMR)
. In this scenario, blockchain can be used to enable the distributed system of
EMR and to enable its security and privacy while data sharing . Blockchain
comes with challenging and technical tasks in these scenarios. There are several
good surveys discusssing basic blockchain concepts, opportunities and applications
[11, 12]. Some papers focused speciﬁc aspects such as security, privacy, scalability,
consensus algorithms and some future challenges [13, 14].
To date, the literature lacks comprehensive study of problems addressed, their
solutions, how authors have validated their proposed solutions and future research
directions. In this work, we will discuss the problems addressed related to these do-
mains in current state-of-the-art. The proposed solutions to the concerned problems
is also summarized and is given in Table 1.
Blockchain in WSNs, VANets, IoTs and Healthcare: A Survey 3
The remainder of this paper is organized as follows: In Section 2, problems ad-
dressed of the current state-of-the art is presented. The proposed solutions to solve
these problems are summarized in Section 3. The validation of the proposed so-
lutions is presented in Section 4 while in Section 5 future research directions are
Platform Problem Addressed Contributions Techniques Future Challenges
Secure and private communication between
vehicles in ITS. 
Proposed security mechanism based on IVTP
to provide P2Pcommunication between vehicles
PoW Wastage of processing powerand
Security and privacy between vehicular networks
in smart city. 
Proposed a Block-VN architecture based
on blockchain in smart city for vehicular networks.
Does not provide security
or experimental analysis.
Data Storage Storage bloating problem in blockchain.  Authors proposed binary ﬁeld random shift
encoding method with low complexity.
Deterministic NC-DS &
The proposed solution is not
resistant to pollution attack.
Traceability data is difﬁcult to maintain on
Blockchain and IPFS based system for
data provenance and query mechanism for tracking.
The tradeoff between the capacity
of packet and storage efﬁciency
needs to be further studied.
Less involvement of users and fakedata
is uploaded to protect the personal information.
Blockchain based incentive mechanism. SHA-256, Merkle tree
Experimental evaluation is based
on a small number of samples. So,
the results can be one-sided.
Resource constrained devices in WSNs.  Designed a Rolling blockchain without PoW Monte Carlo tests Security analysis against malicious
nodes is not provided.
Data barriers between MNOs.  Mutual trust based data sharing framework with ﬁne
grained access control
PBFT Computation overhead
Research data rights management.  Provides a method for managing rights of digital
reuse of data using blockchain and smart contracts.
To maintain the data requester in
line with deﬁned terms, incentive
mechanism can be integrated.
Centralized energy trading system.  Chord based distributed system for decentralized
The strategy to prevent numerous
attacks, especially for overlay net
work, is needed.
Centralized access management framework for
IoT have some limitations. 
Distributed IoT system based on blockchain PoC
The solution proposed does not
achieve better performance in the
case of a single management hub.
Latency overhead, bandwidth consumption,
security and privacy concerns in IoT.
Proposed hybrid smart city network with the
technology of blockchain and SDN architecture.
Argon2 based PoW
The proposed system model needs
efﬁcient utilization of edge nodes
and related work can be carried out
by facilitating cache memory at the
Privacy and security issues in IoT data management.
Distributed IoT system based on blockchain. BFT
Privacy protection of IoT data is
not managed. Huge network trafﬁc
overhead because of BFT.
Wastage of storage in existinghealthcare data sharing
Proposed efﬁcient data sharing scheme known
as MedChain and provide required security
requirements in healthcare data sharing.
Inefﬁcient upload of data, Over
head of operation and latency in
data access for requester.
Lack in current EHR systems for data sharing and
Proposed a blockchain based MedBlock framework
for data sharing and management.
High storage overhead, Data stor-
age problem on databases.
Private and secure storage of medical data.  Proposed a secure storage scheme for medical data
based on blockchain.
PoW Interoperability is not tested, High
Table 1: Summarized Literature Review
2 Problems Addressed
In this section, we discuss the problems addressed by the authors in the existing
4 Fatima et al.
2.1 Blockchain in Vehicular Networks
In this modern era, mechanical vehicles are moving towards automation. Intelli-
gent Transportation System (ITS) uses ad hoc networks for communication between
vehicles, which is not secure. At present, security protocols used for communica-
tion between vehicles are not suitable for ITS applications. So, authors in  pro-
posed a standard security mechanism for ITS. For setting up a trust relationship
between clients in vehicular networks, security and privacy are the main concerns.
The primary security issues of vehicular networks include: examining veriﬁcation
of clients, conﬁdentiality of the message and guaranteeing safe area or location (ve-
hicular network mainly depends on area data). The security and privacy issues of
vehicular network are further investigated by authors in .
2.1.1 Blockchain-based Data Storage
Each node stores all transactions generated by all the previous blocks in blockchain.
Consequently, the volume of data increases linearly with time. The rapid increase
in the volume of data may cause the problems of lack of storage room and unsus-
tainable expansion of system size. The above mentioned problems can be named
as a storage bloating problem. Few works have been done to manage this problem,
however certain amount of information was lost in this work. In , authors re-
solved the storage bloating problem without losing a certain amount of information.
Logistics management systems are emerging day by day. Even though the systems
can automatically trace the complete process, the provenance data can be tampered
in the traditional systems. As the blockchain was designed for digital transactions
so it has limited storage and it is is difﬁcult to maintain the traceability data on the
2.1.2 Blockchain in WSNs
In , Crowd Sensing Networks (CSNs) collect sensing data by using sensors car-
ried by mobile phones or any IoT devices to save cost. The main issue of CSN is
the leakage of privacy. The privacy leakage problem results in less involvement of
users and false data is uploaded to safeguard their personal information. WSN nodes
and mobile devices have a limited number of resources. The usage of a blockchain
network in smart sensor networks is impossible because sensors are resource con-
strained devices and do not have enough computation power to perform PoW con-
sensus algorithm. The blockchain network requires a permanent connection between
nodes, which is not energy efﬁcient. So, the blockchain without PoW is required,
which allows partial connectivity at the same time as to resist errors and adversary
Blockchain in WSNs, VANets, IoTs and Healthcare: A Survey 5
2.1.3 Blockchain-based Data Sharing
Mobile communication and networking lead to the creation of a very complex sys-
tem. Artiﬁcial Intelligence (AI) based network frameworks are introduced to operate
the network automatically. However, mobile network operators are currently facing
the problem of data barriers. So, a framework for data sharing based on mutual trust
was established to break barriers of data between different mobile network opera-
tors . The main barriers of data sharing in research are due to the fear of misuse
of data and its wrong interpretation. Authors in  proposed a secure network to
share research data so that the owner can oversee how the data is being accessed
and reused. The demand and supply of energy is increasing day by day. For this pur-
pose, energy suppliers and consumers are there to buy and sell energy, this is known
as energy trading. The present centralized state of energy trading system is facing
security and privacy problems. The decentralized energy trading based on Bitcoin
protocol was proposed, which lacks the description of attacker performance. For
the management of energy, green blockchain concept was introduced, which lack
the details of security issues in the proposed system. So, an efﬁcient energy trading
system was proposed in  for the loss of transmission in the smart grid.
2.1.4 Blockchain in IoT
With the growth of IoT, the management of an enormous number of IoT devices is
a technical challenge. Existing management frameworks for IoT are based on cen-
tralized models and their applications have some limitations in scenarios with large
number of IoT devices . With the rise of IoT devices, smart cities are being de-
veloped. As the volume of data increases, it leads to latency overhead, bandwidth
consumption and issues in security and privacy concerns. Today’s smart city net-
work requires to bring computing and storage resources closer to the endpoint .
Data management of a large number of IoT devices is a critical issue. Existing so-
lutions used centralized systems for controlling IoT devices, which bring issues of
privacy and security in IoT data management. Blockchain has been used in the ﬁeld
of IoT because it provides decentralization, immutability and traceability. However,
due to the issue of scalability and high cost of resources, it is not trivial to employ
blockchain in IoT scenario .
2.1.5 Blockchain in Healthcare
According to authors in paper , existing blockchain-based healthcare solutions
are not efﬁcient enough to share data from IoT devices. Data from IoT devices are
stored in chunks and to access the data stream the entire chunks of data need to
be accessed. The existing scheme downloads digest of each chunk and checks the
integrity of all of them, which is not an efﬁcient process. Since the information
stored on the blockchain is immutable, so the transitory information such as crypto-
6 Fatima et al.
graphic keys and location of actual data cannot be removed after data sharing. This
transitory information results in wastage of storage. With the application of IoT in
healthcare, a large amount of data is shared, and storage overhead is an unresolved
problem. Consequently, efﬁcient sharing of healthcare data becomes a nascent prob-
lem. To achieve the excellence of healthcare providers and to make the healthcare
system smarter, sharing of data and medical records is the key step. Data sharing in
healthcare is done between individuals such as sharing of patient’s data with stake-
holders. In today’s healthcare systems, patient scarcely has access to the healthcare
data. Blockchain plays a vital role in increasing the collaboration between patient
and healthcare industry and enables a secure and appropriate mechanism for shar-
ing Electronic Health Record (EHR) . EHR is considered as valuable asset for
patients and although, private and secure storage of medical data is a critical issue.
In , authors addressed the issue of secure storage and sharing of medical data.
The following section describes the contributions and the solutions proposed by the
3.1 Blockchain in Vehicular Networks
In , authors proposed a security mechanism based on blockchain for secure and
intelligent vehicles communication. Authors introduced branching and unbranch-
ing of Local Dynamic Blockchain (LDB) for achieving efﬁciency. Intelligent Vehi-
cle Trust Point (IVTP) is introduced to provide Peer-to-Peer (P2P) communication
between vehicles without disturbing other intelligent vehicles and provides trust
between vehicles without exposing their private information. Two blockchains are
proposed in this mechanism to overcome the challenge of data storage and man-
agement. Authors proposed a Block-VN model based on blockchain in a smart city
for vehicular networks . The proposed model allows vehicles to share their re-
sources and create a network to generate value added services. Service scenarios
and principles of requirement are also discussed in this paper.
3.2 Blockchain-based Data Storage
Authors in  tackled storage bloating problem, using Network Coding based Dis-
tributed Storage (NC-DS) without losing any information. Deterministic NC-DS
and rateless NC-DS are the two implementations of NC-DS. Rateless NC-DS has
large encoding and decoding complexity, which is not suitable for devices with lim-
Blockchain in WSNs, VANets, IoTs and Healthcare: A Survey 7
ited computing and energy resources. Therefore, authors proposed a low complexity
design method known as binary ﬁeld random shift encoding. The proposed solution
provides a major improvement in saving storage space. In , authors proposed a
system with the combination of Inter-Planetary File System (IPFS) and blockchain
for data provenance, and query mechanism for tracking agricultural products. Large
amount of provenance data from IoT devices is stored on IPFS and hash addresses
of corresponding data is stored on blockchain. Each transaction on blockchain stores
the hash of previous transaction which ensures traceability and usability of data.
3.3 Blockchain in WSNs
To solve the problem of privacy protection, authors proposed a blockchain based
incentive mechanism. The proposed network in  is divided into three parts: CSN,
confusion mechanisms and blockchain. The server receives sensing data from the
blockchain and publishes the information of task. Confusion mechanism process
the data of nodes present in the CSN to achieve the effect of unclarity and privacy
leakage is prevented. In addition, coins are rewarded after successfully storing user
data on the blockchain. More the users participate, the more coins are rewarded
to them. So, the proposed solution increases the involvement of user and provides
privacy protection. Authors proposed a blockchain with several parts and each part
contains a constant number of generated blocks. The amount of blocks depends
on the resources of devices in the IoT network. The concept of rolling blockchain
proposed in  is used to build a WSN with smart cars as nodes of the network. A
mathematical model is created for the formation of the blocks and its structure in
3.4 Blockchain-based Data Sharing
In , authors proposed a ﬁne-grained access control data sharing framework and
data security is improved by smart contracts and permissioned blockchain. Two
types of blockchain: DataChain and BehaviorChain are combined to provide a trust-
less environment for data sharing and supervision of access control. Authors in 
proposed a method for managing rights of digital reuse of data using blockchain and
smart contracts. The new mechanism allows the user to deﬁne reuse terms and pro-
vides a way to track and validate the execution of terms. In , authors proposed
an overlay network based on a chord-based distributed system in a decentralized
energy trading system, which ﬁnds the location of nodes among neighbours. The
system is based on blockchain and possible security issues are analyzed.
8 Fatima et al.
3.5 Blockchain in IoTs
To overcome the aforementioned problems in , authors proposed a distributed
IoT system based on blockchain. Proof of Concept (PoC) architecture that uses
blockchain to implement access management system for IoT is presented. The ac-
cess control permissions for different IoT devices are stored in blockchain. The pro-
posed solution is suitable for horizontal scalability, where WSNs are connected to
multiple management hubs. Smart city network with the technology of blockchain
and Software Deﬁned Networking (SDN) architecture was introduced. Authors pro-
posed Argon2 based PoW scheme for security and privacy and ensured the integrity
of data. The network proposed in  consists of core and edge network, which
helps in achieving properties of a centralized and decentralized network. For ef-
ﬁcient and secure data management in IoT, authors proposed a cross-chain based
framework in . They integrated tangle into the blockchain network and built a
cross-chain based framework for IoT data management. To overcome the challenge
of scalability of IoT blockchain, authors used tangle, which uses a Directed Acyclic
Graph (DAG) data structures, and divide the data into several small sub-Tangles
just like side chains. The sidechains are then connected to form a decentralized net-
work. Decentralized consortium blockchain connects the sub-Tangle with itself and
securely logs incoming requests for data access control and execute access control
mechanism on these requests.
3.6 Blockchain in Healthcare
Authors proposed a new data-sharing solution known as MedChain , which is
based on two decentralized networks. P2P storage, which stores mutable data such
as a description of data and session. Second is the blockchain network which stores
immutable data, for instance, data digest. By separating mutable data from the im-
mutable, description of data is effortlessly updated and does not results in a further
overhead to the blockchain network. For the veriﬁcation of the data stream, a new
digest chain is introduced, and for the reduction in storage overhead, a session is
introduced, which helps to remove the transitory or mutable information. In ,
authors proposed a Medblock framework for data management and data sharing
in EHR based on blockchain and improve the sharing of medical information. By
this framework, patients can access the EHR of different hospitals by getting rid of
the previous healthcare data stored in segments on innumerable databases. Authors
proposed a blockchain based secure storage scheme for medical data sharing. In
the proposed scheme , authors explained three types of permissions of transac-
tion bodies. Authors also designed structure of block and key roles of blockchain
in healhcare scenario. The introduced blockchain can provide patient EHR without
Blockchain in WSNs, VANets, IoTs and Healthcare: A Survey 9
In this section, the discussions of the experimental results of existing works in liter-
ature are given.
4.1 Blockchain in Vehicular Networks
In , the average time taken for the veriﬁcation of State Change (SC) increases
as the load on the system increases. The tests are performed using the branching of
LDB, to compare the performance of branched LDB with unbranched. For the load
of 2400 SCs/min, the average time taken for SC validation has decreased sharply for
LDB with four branches. The branching of LDB results in speeding up the process
of consensus algorithm. When the load is further increased up to 3200 SCs/min, the
average time taken for SC validation has decreased and the results of LDB with four
branches are much better than unbranched blockchain. In , the authors do not
perform any security or experimental analysis.
4.2 Blockchain-based Data Storage
In , authors analyzed their proposed solution based on storage, bandwidth, con-
sensus speed and scalability. Deterministic NC-DS uses half of the storage room
as compared to the traditional blockchain system and rateless NC-DS uses slightly
large storage room as compared to the deterministic NC-DS. In the proposed solu-
tion, the volume of data to be distributed is half of the original. There is no effect on
the consensus speed and the framework is scalable. The scheme in  is validated
on the basis of data uploaded per minute versus data processed per minute. As the
amount of data increase, the processed data continue to increase.
4.3 Blockchain in WSNs
In , experiments are performed on android studio and eclipse. Data is collected
from hundred people and the experiments performed show that men are more con-
cerned about privacy than women. The proposed solution has less time complexity
as compared to the existing one. The results from the simulations show that with the
increase in a number of lost connections and nodes, the network remains unaffected
and blockchain can be formed. Monte Carlo tests are performed to numerically ﬁnd
the alternative path, when the position of links with different node densities is re-
moved randomly. In , the results show that as the level of attack increases the
10 Fatima et al.
network is unable to provide alternative paths until it seizes up. In the scenario with
low sensor density, the network seizes up at low intensity of attacks.
4.4 Blockchain based Data Sharing
Proposed system in  provides privacy, security and scalability. Privacy is pro-
vided by encryption of data and then the data is stored on cloud database. Only
hashes are saved on blockchain for integrity veriﬁcation. The PBFT consensus al-
gorithm is used which does not create a hurdle to scalability. In , authors provide
a brief analysis of transaction costs of execution of functions in smart contracts and
the actual execution cost. The total cost for executing smart contracts is less than
two US dollars which is negligible as compared to other open access publishing
expenses that can easily go over one thousand US dollar. In , authors analysed
security issues such as selﬁsh mining and double spending attack. The results show
that approximately thirty percent of blocks are generated between ten minutes.
4.5 Blockchain in IoT
Authors in  performed evaluation of existing management systems against pro-
posed solution. The evaluation shows that the proposed solution is more scalable
than conventional scenarios when the load of IoT devices is distributed among nodes
of blockchain network. The experiments performed show that the difﬁculty in the
proposed scheme is regulated based on the hash rate. The proposed scheme in 
performs more efﬁciently as the size of the block depends on the number of trans-
actions per second and it is more robust as the system proposed has desired average
time per block. The latency is also reduced as compared to the public Ethereum
blockchain. The throughput and latency for different transactions in a network are
tested under different conﬁguration environments in . As the memory and num-
ber of CPU cores increases, the throughput of the network becomes closer to the
default send rate value, and latency of processing of transactions is also decreased.
With memory and CPU, network trafﬁc of the system is also tested. The trafﬁc over-
head is evaluated by monitoring incoming and outgoing trafﬁc of the peer container
of Fabric network.
4.6 Blockchain in Healthcare
The proposed scheme in  is validated based on a delay in data retrieval. The
breadcrumb mechanism proposed in this work helps the user to directly retrieve the
useful information instead of traversing the whole block until the useful or required
Blockchain in WSNs, VANets, IoTs and Healthcare: A Survey 11
information is found. As the number of users increases, the efﬁciency of data re-
trieval is signiﬁcantly improved. The efﬁciency of the system is also improved by
uploading data asynchronously to avoid system congestion and high load on the sys-
tem. Authors validated the proposed scheme in  on the basis of communication
overhead, storage overhead and scalability. In this work, the digest of the data stream
is encoded into a digest chain. This scheme can avoid communication overhead as
to perform data integrity check, only the last chunk of data needs to be extracted
instead of downloading the whole stream. The storage overhead is also removed,
as only the ﬁngerprints are stored on the blockchain and other mutable information
is stored in the directories. The scalability is validated by increasing the number of
directory nodes. As the number of directory node is increased, the response of the
system also increases sub-linearly. The proposed system in  is analyzed with tra-
ditional systems, which proves that it can provide privacy protection, secure storage
and is tamper proofed.
5 Limitations/Future Directions
In this section, we outline the limitations or future research directions of the existing
5.1 Blockchain in Vehicular Networks
In , branching comes with shortcomings of a high amount of duplicate SCs em-
bedded in blocks. As the load on the network increases, the number of duplicate
SCs per block is rapidly increased. The duplicate SCs lodged in blocks result in the
wastage of processing power and storage. The proposed model in  is not ana-
lyzed on the basis of security and experiments. The model needs further investiga-
tion to combine public storage of blockchain with distributed ﬁle system to manage
security, scalability and transparency.
5.2 Blockchain-based Data Storage
In the proposed scheme , each node stores distinct encoded packet so the error in
the single node can propagate to a large area. So, the basic assumption of blockchain
that adversary cannot compromise more than half of the resources of the system is
not followed in the proposed framework. The trade off between capacity of packet
and storage efﬁciency needs to be further studied in .
12 Fatima et al.
5.3 Blockchain in WSNs
In , the experimental evaluation is based on smaller number of samples and the
results can be one-sided and privacy protection can be enhanced with the improve-
ment of algorithm. The security analysis and protection against malicious nodes
are not provided in . The proposed method can be extended to other topological
models with the integration of a Merkle tree.
5.4 Blockchain-based Data Sharing
In , two types of blockchain may result in computation overhead because mining
is performed on both DataChain and BehaviorChain. The proposed method in 
does not provide an incentive mechanism such as rewarding ethers or tokens when-
ever new data set is published, so that the participants stay in line with the deﬁned
terms. The strategy to prevent numerous attacks, especially for overlay network, is
needed in .
5.5 Blockchain in IoTs
The solution proposed in  does not achieve better performance in the case of a
single management hub. The proposed system model in  needs efﬁcient utiliza-
tion of edge nodes and related work can be carried out by facilitating cache memory
at the edge nodes. The proposed privacy access control scheme in  only ensures
privacy and protection of IoT data, privacy protection of user data is not considered.
The Byzantine Fault Tolerance (BFT) consensus algorithm is used, which has huge
network trafﬁc overhead.
5.6 Blockchain in Healthcare
In [25, 26], authors have stored the data on the database, which results in latency
overhead. Authors also do not provide a ﬁne-grained access control to the client for
data sharing. The solution proposed is unable to provide the record of data access
and how data is used by the requester. In , patient’s manual approval is needed
every time data is accessed, which results in the overhead of operation and latency
in data access for requester. The healthcare providers also manually upload data on
directory and blockchain network, which is inefﬁcient. The interoperability of the
proposed system  is not tested, and it is not energy efﬁcient because PoW is
used, which needs high computation power.
Blockchain in WSNs, VANets, IoTs and Healthcare: A Survey 13
In this paper, we described the recent state-of the-art related to the applicability of
blockchain for WSNs, VANets, IoTs and healthcare. Moreover, we presented the de-
tailed literature review which shows that adopting blockchain for above mentioned
scenarios is still in its initial stages. There exists many future challenges and di-
rections related to privacy, security, storage, consensus algorithm, scalability and
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