=Paper=
{{Paper
|id=Vol-3390/CEUR-Template-1col
|storemode=property
|title=Implementation of Property Rental Website Using Blockchain
with Soulbound Tokens for Reputation and Review System
|pdfUrl=https://ceur-ws.org/Vol-3390/Paper3.pdf
|volume=Vol-3390
|authors=Sanskar Sharma,Aryan Kumar,Nidhi Sengar,Ajay Kumar Kaushik
|dblpUrl=https://dblp.org/rec/conf/snsfait/SharmaKSK23
}}
==Implementation of Property Rental Website Using Blockchain
with Soulbound Tokens for Reputation and Review System
==
https://ceur-ws.org/Vol-3390/Paper3.pdf
Implementation of Property Rental Website Using Blockchain
with Soulbound Tokens for Reputation and Review System
Sanskar Sharma 1, Aryan Kumar 1 , Nidhi Sengar 1 and Ajay Kumar Kaushik 1
1
Maharaja Agrasen Institute of Technology (GGSIPU), PSP Area, Plot No. 1, Sector-22, Rohini, Delhi-110086,
India
Abstract
The rising number of rental scams is a concern for the community as certain illegal practices
tarnish the sector’s image. Landlords rent the property without a written rental agreement to
charge excessive maintenance charges, tenants provide wrong background information or
refuse to pay rent or maintenance, and so on. This paper proposes introducing a decentralized
profile reputation system using soulbound tokens and digital currency for transactions in rental
listing websites to minimize the number of rental frauds. A non-transferable non-fungible token
is provided to the new user that records their reputation across their time on the website. The
lease agreement is secured via a smart contract and only initiates once the security deposit has
been paid by the selected tenant and signed by the landlord. All rental transactions take place
on-chain, and only registered users with a tenant-landlord relationship can give reviews. This
ensures the credibility of the review system. The decentralized ledger can also be used to
supervise property rental affairs. This method facilitates convenient and authentic background
checks, easy transactions, and market supervision.
Keywords 1
Blockchain, Soulbound Tokens, Real-estate, Reputation building, Rental Website, Web3,
NFTs, IPFS
1. Introduction
The real estate sector is an important area in stimulating economic growth. Real estate is a type of
property to possess and use. The developments of the real estate sector boosted the growth of retail,
hospitality, entertainment, housing, and services business. An electronic version of the real estate
industry, Internet real estate is the concept of disseminating housing estates for sale or rent online, and
for consumers seeking to buy or rent properties through such platforms. The Internet real estate industry
has faced several criticisms due to the lack of rules and regulations to protect developers and buyers.
People who are looking to rent a property are often caught in housing and lease scams. In such cases,
deceivers show themselves as either brokers or owners of the desired unit and tell the interested tenants
to make transactions to their accounts for renting the house. Once the amount is transacted, they escape
and disconnect with the renters. Tenant scams on the other hand take advantage of unassuming landlords
who fail to implement the right procedures for screening renters, writing contracts, and collecting
payments. Scams can take many forms and can be costly for landlords, both in terms of time and money.
Some common examples include submitting false employment records, faking credit reports, forging
checks and pay stubs, attempting to reset the eviction process, stealing a landlord's listing, and hiding
property damages. These types of scams can put a landlord's income and business at risk. Today,
International Symposium on Securing Next-Generation Systems using Future Artificial Intelligence Technologies (SNSFAIT 2023), May 05-
12-2023, Delhi, India
EMAIL: sanskarsharma1822@mail.com (S. Sharma); aryankumar05@gmail.com (A. Kumar); nidhisengar@mait.ac.in (N. Sengar);
Ajayk08@gmail.com (A. K. Kaushik)
ORCID: 0000-0003-2431-5587 (S. Sharma)
©️ 2020 Copyright for this paper by its authors.
Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR Workshop Proceedings (CEUR-WS.org)
21
numerous landlords and property management companies in urban corridors have transitioned from in-
person dealings with rental applicants to digital interactions to cater to customer preferences. However,
this has made it more difficult to verify application validity. In fact, between 2016 and 2018, 97% of
property management companies have experienced fraud in some capacity, with 80% experiencing it
up to 20 times, according to the Forrester study. Overall, about 59% of rental applications are submitted
online, and this digitization of the rental application process has opened new avenues for fraud. The
shift from in-person to digital applications, coupled with the COVID-19 pandemic, has also played a
role in the increase of fraud in the rental housing industry.[1]
1.1. Proposed Solution
To solve such problems, the paper proposes the use of a property rental website which uses
blockchain as its main technology. This will be achieved by minimizing online rental fraud and
introducing profile reputation using Soulbound Token (SBT) for customers. It will allow tenants to look
for available rental options, and landlords to list their properties. A Soulbound Token will be issued to
the user that will monitor their profile reputation and authenticity. A soulbound token is a publicly
verifiable and non-transferable non-fungible token (NFT) that can be used to represent an individual’s
credentials, affiliations, and commitments. Landlords can list their properties in the form of smart
contracts on the network. A smart contract is a paperless digital code that defines a set of promises on
prewritten conditions that the parties of a transaction have agreed upon [2]. Listing involves paying a
minimal crypto fee to the admin as a security deposit which can be liquidated if the user violates the
terms and conditions. A rental agreement only initiates once the tenant has successfully deposited the
security fees which can further be retrieved when the agreement period ends. The terms and conditions
of rent between the parties will be secured via a smart contract and all transactions henceforth will take
place via smart contract methods. These programs are executed on a decentralized network of
blockchain that provides the benefit of being immutable. Only users that have been in the tenant-
landlord relationship can give reviews to each other, thus ensuring that the review system is credible.
This could help revolutionize the online rental industry by minimizing the number of frauds and scams
and increasing the trust between landlords and tenants.
22
Figure 1: Use Case Diagram
2. Technical Background
2.1. Blockchain
Blockchain is an open, distributed ledger that records transactions between parties efficiently and in
a verifiable and permanent manner. The present state of blockchain is often compared to that of the
Internet in the mid-1990s, still in its infancy, when its value and potential were not understood. A
blockchain is a decentralized and digital system that records transactions or events across multiple
devices and locations. It functions as a public ledger of all the activities that the participating parties
have conducted. The system uses the consensus of its participants to validate each transaction and once
entered, it cannot be altered. One of the primary advantages of blockchain technology is its increased
security and transparency, which fosters trust among participants. But its benefits go beyond that, as it
also improves speed, efficiency and automation, resulting in significant cost savings. The use of
blockchain technology reduces paperwork and minimizes errors, leading to less overhead and
transaction costs, and in many cases eliminates the need for intermediaries to verify transactions. Every
user has a wallet address associated with them which is used to carry out transactions on the chain. One
of the crucial features of blockchain is its transparent nature. The transaction is visible to all the users
on the chain and thus any type of fraud or deceit can be caught by the nodes of the chain and such a
user is removed from taking part in any other activities of the chain.
Figure 2: Blockchain Structure
The immutable attribute of blockchain is credited to its structure. The chain is built up by segments
called blocks. Every time a transaction takes place, the nodes mine a block, generating a unique hash
with its header. This hash is then used as an input in the next block to be minted and thus forms a chain.
If any user tries to tamper with the data, they end up with a hash different from the other nodes of the
chain. And as soon as such action is detected, the node is removed from the chain. Advantages of using
blockchain to pay rent [4]:
1. Increased flexibility: Blockchain-based payments enable digital and mobile transactions,
allowing landlords and tenants to make and receive payments 24/7, with no restrictions of
traditional banking hours.
2. Easier cross-border payments: - Renting internationally can be challenging, especially when
dealing with different currencies. Cryptocurrency allows for immediate, low-cost international
transactions, saving time and money for both parties
3. Lower transaction fees: Online rental platforms often impose fees for credit card payments,
typically 2.5%-2.9% of the rent amount, paid by the tenant. However, by using cryptocurrency,
both parties can avoid these fees and potentially save hundreds or even thousands of dollars
over time.
23
4. Greater privacy for renters: - Blockchain-based payments also provide increased privacy for
tenants, as it uses anonymous addresses that change for every transaction. This means that
payments do not require personal information, credit card numbers or account numbers, making
the transaction untraceable.
2.2. Smart Contracts
A smart contract is a paperless digital code that describes a set of contracts on prewritten conditions
that the parties of a transaction have decided upon. The parties interacting can set conditions that can
launch a series of actions when required or when the conditions are met [2]. The use of smart contracts
can automate the process of managing rental properties, enabling efficient and streamlined operations.
For example, a smart contract can be used to automatically gather rent payments and distribute them to
the landlord, or to automatically initiate the eviction process if a tenant fails to pay rent. Overall, the
usage of smart contracts in the real estate industry can enhance the efficiency, safety, and transparency
of property transactions and surveillance.
2.3. Reputation
Reputation systems operate by establishing trust relations based on evidence of a party’s past
behaviour. These systems rely heavily on trust data as the primary form of exchanged information. Such
systems maintain mechanisms to monitor and record the reputations and credibility of participants [5].
2.4. Non-Fungible Token (NFT)
A non-fungible token is a unique, digital asset stored on a blockchain, that cannot be replaced by
another identical asset. The term ”fungible” originates from economics and accounting, referring to
items that can be exchanged for equivalent items. Common forms of currency, like cash, are fungible
as they are considered of comparable value and can be used as a medium of exchange. NFTs are unique,
one-of-a-kind tokens, which makes them non-fungible [6].
2.5. Soulboud Token (SBT)
A soulbound token is a type of non-transferable, non-fungible token that can be publicly verified
and represents an individual’s credentials, affiliations, and commitments. These tokens are used to track
reputation and are added to addresses but cannot be bought or sold [7].
2.6. InterPlanterary File System (IPFS)
The InterPlanetary File System (IPFS) is a decentralized method for sharing and accessing files
through a peer-to-peer network. Unlike traditional systems which rely on a centralized server, IPFS
utilizes a distributed network of nodes to store and distribute data. This allows for the sharing and access
of a variety of content including documents, images, audio and video files, and more, all without the
need for a centralized server infrastructure.
2.7. Uniform Resource Identifier (URI)
A Universal Resource Identifier (URI) is a string of characters that identifies a name or a resource
on the Internet. URIs can be broken down into two types: URLs (Uniform Resource Locators) and
URNs (Uniform Resource Names). A URL, or Uniform Resource Locator, is a subset of URIs (Uniform
Resource Identifiers) that identify the location of a resource on the Internet. For example,
24
https://www.example.com/index.html” is a URL that identifies the resource located at the root of the
”example.com” domain, which is an HTML file named ”index.html”.
3. Related Works
The applications and need for soulbound tokens were introduced by Weyl in 2022 [8]. This paper
presents the importance and necessity of a decentralized identity in web3. It depicts how non-
transferable tokens can be used to build trust across economic activities and personal brand building.
Hildebrandt further worked on establishing soulbound tokens as a method for an authentic decentralized
profile in the anonymous network of blockchain accounts [9]. The relationship between user experience
and customer reviews has also been studied and evidence of the role of reviews in trust building has
been established. Askalidis & Malthouse demonstrated this through an analysis of the number of
reviews to the conversions rate in 2016 [10]. The findings indicate about a 270% increase in conversion
rate. The equation used includes an exponential deterioration of the weightage of reviews with time.
Varma also conducted a study in 2020 to indicate the impact of social media identity in e-commerce
and how this is subjected to reviews. A few studies focus on blockchain immutability for credible
review systems. In 2018, Wang introduced the utilization of the blockchain ledger to avoid fraudulent
and manipulative reviews [11]. It discusses the importance of reviews in the e-commerce segment. The
system validates a new review by verifying the identity of purchasers. There are significant studies on
the subject of peer-to-peer reputation systems and their importance. Works by Battah in 2021, Mekouar
in 2009 and Dennis & Owen in 2015 [5,12,13] describe the disadvantages of the centralized reputation
system. These studies show how the current system is prone to attacks, as well as how merchants and
other entities can profit from these attacks on centralized servers which manage the stature of all users.
The characteristic of transparency and immutability of blockchain makes tampering with such data
extremely difficult. An attacker must have access to the majority of the chain, to manipulate data (51%
attack), which gets exponentially harder as the number of active nodes on the chain increases. In 2018,
Karamitsos implemented blockchain in the field of real estate utilizing its immutability, transparency
and security [14]. The paper extends the advantages of decentralization to the real estate sector and
proposes the use of smart contracts for securing sensitive data such as rental agreements, ownership
papers etc. It further depicts the uses of smart contracts in tackling problems of real estate such as
modification of data, lack of trust among parties and need for intermediation. Wang demonstrated a
housing rental system using a redactable blockchain. A landlord would submit the documents verified
by a trusted third-party organization to the accounting node, which after verifying will list the property
to insure credibility. Xue worked on introducing an alliance chain to this system [15]. An alliance chain
is a decentralized organizational structure in which multiple organizations can participate. It allows
landlords to list their properties on the application, and tenants to submit their applications, which are
then verified by the alliance chain. Once the tenants' intentions are cleared, the data is added to the
chain.
4. Proposed Method
The present methods of online rental systems in real estate have posed certain problems. For
example, there is no way to track the authenticity of the customer or the landlord and hence committing
a scam on either end is highly likely. The terms and conditions of the contract may not be clear and can
be altered to suit either party. To tackle this, the system will be introduced on blockchain and SBTs will
be used for profile reputation with the help of an online rental website. Steps involved:
● Upon successful registration, an Entry Token SBT will be issued to the user who may enter as
a tenant or a landlord. This token will be used to track the reputation, number of properties etc.
of the user. After this, every time the user tries to log in, it checks for the Entry Token Id
associated with the user’s wallet address and if the user is blacklisted due to their reputation
having a value less than the minimum set in terms and conditions.
25
Figure 3: Sample Entry Token URI
● If the user is a landlord, they will have the option to list a property. A separate contract will be
created for all individual properties. The property data including information such as property
images, rent, location, current reviews etc. are hosted on IPFS and stored in their respective
smart contracts. This data is also kept in a centralized server to facilitate the searching of
properties using required filters. Changes will be triggered to modify the landlord’s Entry
Token upon listing a property.
● If the user is a tenant, they can approach the listed property. After successful negotiations and
commitments, the tenant pays the security deposit. After this, an SBT called Deal Token will
be issued to the tenant via the property contract. The tenant period will also commence
henceforth, storing the due dates of rent and the termination period of the contract. The
agreement cannot be terminated before the set tenure end date unless both parties agree or if
anyone violates the terms and conditions stated. In case the tenant violates the rental agreement,
the landlord has the right to revoke the security deposit.
● The tenant can pay the rent and have access to other features of the property as long as the Deal
Token associated with the particular property is valid. During this time, the landlord can review
the tenant and vice-versa. The reviews will remain on the Entry Token of both users and the
contract forever. Since only the members with a tenant-landlord relationship can review each
other, the possibility of review bombs is minimized and the credibility is increased.
● After the contract period is over, the Deal Token will be maintained in the Entry Token of the
tenant and they can withdraw their security deposit. The tenant record is updated in the property
contract.
4.1. Smart Contracts and their Functionalities
1. Admin.sol - Admin.sol is the administrative smart contract. It is used to monitor the
market status and provide Entry Token SBT to all new users. The mapping of Token
Id to Token URI is used to retrieve user data stored on IPFS. Gas: 2590763 gas;
Transaction cost: 2252837 gas.
2. PropertyFactory.sol - PropertyFactory.sol is a smart contract that is used to deploy
Property contracts in real time. This contract is accessible only to verified members or
users with an Entry Token Id provided by the admin. A user willing to list their property
can access the functionality of this contract to upload property data and pay minimal
collateral to the admin. This deposit can be liquidated on the violation of the terms and
conditions. Gas: 4294054 gas; Transaction cost: 3733960 gas.
3. Property.sol (Template) - Property.sol is a template smart contract. Each property listed
on the website has its Property contract deployed with its data in the state variables.
This contract is used to mint Deal Token SBTs and provide these to the selected tenant
26
after they have paid the property security money. This amount is stored in the contract
and can be retrieved back by the tenant once the rental agreement has successfully
ended. The contract contains an array of reviews given to the property and all methods
necessary for all other rental transactions. Gas: 3828185 gas; Transaction cost:
3328856 gas.
4.2. Equations
The reputation system is a vital component of the website as it implements accountability. The most
recent behaviour has slightly more relevance over past experiences, therefore the equation must give
priority to the current review. In the case of rental review history, all conduct is crucial. Thus, the weight
of reviews must not degrade [5]. The review system is based on a star rating system with a range of
[1,5], where 1 indicates multiple violations and 5 indicates excellent behaviour. The use of 1 −
𝑙𝑜𝑔5 𝑥 ensures that each rating holds different graveness and each rating directs to an appropriate
degradation of reputation. The equation for determining a user's reputation score is
[1.01 × (𝑅𝑚𝑎𝑥 − {𝑅𝑚𝑖𝑛 × [1 − 𝑙𝑜𝑔5 𝑥]})] + [𝑅 × (𝑛 − 1)] (1)
𝑅 =
𝑛
where R is the current reputation score stored on the Entry Token URI. 𝑅𝑚𝑎𝑥 is the maximum
reputation score allowed. It is set to a constant value of 100. 𝑅𝑚𝑖𝑛 is the minimum reputation score
possible. It has a constant value of 50. 𝑛 is the total number of reviews. 𝑥 is the current rating score
given which falls in the range [1,5]. The current rating score is multiplied with a factor of 1.01 to give
higher weightage to the latest reviews over older ones [5].
The sum of current The current reputation must not exceed the maximum reputation score allowed.
Equation (2) is used to prevent overflow.
𝑅 ≥ 𝑅𝑚𝑎𝑥 ⇒ 𝑅 = 100 (2)
If a user’s reputation score falls below this threshold, their collateral will be liquidated and their low
score on the Entry Token will prohibit them from accessing the website in the future. Equation (3) is
the liquidation equation.
𝑅 < 𝑅𝑚𝑖𝑛 ⇒ 𝑅 = 𝑅𝑚𝑖𝑛 (3)
4.3. Performance Analysis
4.3.1. Cost
Securing the data stored is an essential part of the system. This data includes sensitive information
such as rental agreements, verification documents, ownership papers, images and property data and the
reviews of users and properties. Data storage can have one of three approaches - a centralized cloud
system, a decentralized storage IPFS, and storing all data on-chain. While the first approach is the
quickest and most cost-efficient, it does carry the disadvantage of being centralized. Between the latter
27
two, the unit of measurement is the gas used. The cost of storing a 256-bit word on the smart contract
is 20k gas [16].
Table 1
Difference in cost of storage methods
Storage Method Gas Used approx.(1kb data) Cost[17](in ETH)
Storing data directly in smart 640,000 0.029356
contract
Storing the IPFS hash of data in 85,000 0.003898
the smart contract (string)
While both approaches provide the same immutability and security to the data, the gas used in storing
data on-chain is huge, making it an extremely expensive process. Therefore, it is not a viable method
to store data such as property images or contract documents, that can be multiple and can have a size of
more than 1kb directly on the chain.
4.3.2. Time
Renting or finding a lease property can be a tedious and labour-intensive process. Clients may have
to wait several days for a formal agreement, and additional paperwork can prolong the process. The
presence of both parties is also required to prevent deceit. This can be reduced by introducing the
blockchain. Automating each process reduces the overall time. Using SBT also reduces the time to
check backdoor references. decentralized applications further make the concept of long-distance rentals
easy and secure. The time taken for the agreement is subject to negotiation between the two parties. The
collection of rent, maintenance or other fees can be done by one withdrawal transaction. Reading data
that the SBT holds from a blockchain is relatively quick. Other operations such as writing data or
making transactions can take longer, depending on the specific blockchain, the speed of the network,
and the complexity of the operation. The average time taken to add a block to Ethereum is
approximately 14.4 seconds [18].
4.3.3. Security
The decentralized ledger of blockchain offers the advantage of being immutable and transparent. All
transactions across the system are visible to members. Most blockchains use consensus algorithms to
ensure that the data recorded on the blockchain is accurate and valid. These algorithms require multiple
nodes on the network to reach a consensus about the validity of a transaction before it is added to the
blockchain. The security of the data helps to transform the network from a trust-based system to a
cryptographic-guarantee-based network. Blockchains use cryptographic hashing to secure the data
stored on them. Cryptographic hashing involves taking a piece of data and running it through a
mathematical algorithm, which produces a unique ”hash” that represents the data. This hash can be used
to verify the authenticity of the data without revealing its actual content.
5. Conclusion and Future Scope
In conclusion, the security and time-saving advantages provided by the model can act as a method
to improve the current state of online property rental systems. The applications of SBTs in this field use
the significance of decentralized identities to tackle real-world problems. The reputation of these
decentralized ‘souls’ is utilized and stored on the blockchain. The network provides security to the data
due to its immutable attribute. Uploading data to a peer-to-peer distributed server IPFS instead of any
other cloud services ensures that the data used on the website as property information, rent agreement
28
information and profile information is secure from being tampered with. The confidentiality and
credibility provided by the review system help prevent attacks such as review bombs, that could have a
massive impact on businesses. The model ensures that individuals are saved from the hassle of effort
and time the current system takes. Verification of documents and records can be done within minutes
using the system. The user SBT system also ensures that the members are safeguarded from attackers
that disguise themselves as lawful associates. Such members are detected by the community and
discarded from having access to the app again. The attacker will carry the blacklisted non-transferable
NFT with his wallet thereafter.
Decentralized identities and their application can help improve the blockchain network. Studies for
the use of SBTs in education and healthcare for documents and user data have already shown the
advantages of using SBTs. The model presented uses these applications to counter the less-regulated
systems of online property renting. Introducing blockchain to the sector can help tackle its problems of
speed, safety and fraud. There are several potential areas for future research in this field. One potential
direction is the integration of real estate transactions. Another can be the introduction of an automated
system to report false reviews to improve their credibility. Another area can be around an automated
entity that can verify the documents before they are uploaded on-chain. This can further increase the
authenticity of the listed properties and user profiles.
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