# Policy-Based Smart Contracts Management for IoT Privacy Preservation
### Blockchain Features  
Several advantages offered by the blockchain technology [10] such as decentralization, persistence, immutability, auditability, and consensus, make it an outstanding candidate to enhance the privacy of IoT applications and constrained IoT devices [11; 12; 13; 14; 15]. Blockchain is a distributed ledger technology, which provides secure data transactions and is difficult to be tampered with or altered. Blockchain places more emphasis on the safety of the data themselves, offering immutability and authenticity, as opposed to traditional security systems, which concentrate on the channel that data take. For instance, blockchain technology underpins Web 3.0, a decentralized platform. This empowers users with more control over their data and online activities while ensuring security and scalability [16].  
Taking this advantage into account, in this paper, we further investigate the integration of IoT and blockchain for privacy preservation and propose a new model that leverages the properties of private blockchain and smart contracts to guarantee the privacy of users and their data. Our approach is based on private blockchain technology, since it is ideal for applications demanding high levels of privacy and security [17]. By controlling access permissions, private networks can be easily created and segmented into multiple channels. This ensures that only authorized users can interact with the ledger, protecting sensitive information from unauthorized access [18].  
Most of the current approaches that rely on the use of blockchain technology propose to add a cryptography layer to the blockchain network that already uses encryption and hashing techniques to preserve data privacy [19]. Cryptographic techniques require high processing capacity, which is not available within mobile and IoT devices. Existing blockchain platforms like Ethereum and Hyperledger Fabric already provide robust cryptographic mechanisms, making an additional cryptography layer unnecessary. For example, Hyperledger Fabric safeguards privacy through four primary components:  
1. Encryption and data isolation: employing symmetric encryption to protect transaction details and segregating them from blockchain records.
2. Organizational authentication: using digital certificates to verify the identities of entities participating in the blockchain network.
3. Multichannel information dissemination: creating distinct channels for distributing different types of information.
4. Inter-organizational confidentiality: implementing measures to maintain information privacy among various organizations operating within the same channel.  
The blockchain platform also leverages smart contracts, self-executing programs that automate user interactions with the network and enforce transaction rules. Privacy leaks often occur due to improper use or configuration of smart contracts, an unsolved problem in current approaches. Compared to existing approaches, we outperform them by introducing light and effective policy-based smart contract management to preserve privacy within the IoT ecosystem. Our methodology allows users to define their privacy preferences and automatically generate and execute smart contracts that align with these preferences. Instead of adding a separate cryptographic layer, we propose leveraging the existing cryptosystem within the blockchain platform and focusing more on assisting users in defining their privacy policies.