## 4 Decentralization in IoT Security
### Blockchain Solutions for IoT Trust Issues  
_Authentication:_ To guarantee that no two nodes are fraudulently exchanging data with one another, authentication is performed at both ends of the connection. When choosing an authentication method in the IoT, it is important to take into account the system's hardware, connectivity, power consumption, and security requirements. Because of the preinstalled nature of the keys, the symmetric key model is well-suited for low-resource, low-security devices. When data storage on a device based on hardware needs to be protected, hardware security modules (HSMs) are among the safest options. A trusted platform module (TPM) is a widely used way to store asymmetric keys in unhackable hardware. However, the models are not infallible because they can be tampered with by malicious users. Blockchain, a distributed ledger technology, provides a practical alternative because its data are immutable. As an internal network, a private blockchain can protect the IoT from outside attacks. Successful blockchain authentication in the IoT was implemented using the Authenticated Devices Configuration Protocol (ADCP) defined in [122]. _Identity Management:_ For identification purposes, an identity produced by an identity management system must be able to pass an external authentication process. Common identity management architectures can be broken down into three types: standalone, federated, and centralized [123]. There are three main sorts of people involved in identity management systems: the identity owner, the identity issuer, and the identity verifier. Security flaws in traditional identity management systems such as those described above arise because of the centralized manner of storing information [124]. With blockchain technology, several problems with present identity management systems can be solved [123]. Blockchain-based identity management solutions rely on decentralized identifiers (DIDs) for the authentication of users' online personas [124]. DIDs are digital identifiers that are appended to credentials by an identity issuer and stored alongside those credentials in a blockchain-based system [125]. In this scenario, blockchain supports universal access to a shared ledger of records while simultaneously maintaining strict controls over who can view or modify individual records. There are some existing identity management platforms, e.g., uPort [126], Sovrin [127], ShoCard [128], etc., that allow users to create their own identities on the Ethereum blockchain. _Data Integrity:_ There are a few widely used cryptographic protocols, e.g., the Secure Hash Algorithm (SHA), Rivest-Shamir-Adleman (RSA), etc. However, IoT devices might not have sufficient CPU capacity to perform such complex calculations. Additionally, because IoT nodes are not always running, adversaries have a window of time to compromise information. The authentication and read-write safeguards proposed as a solution may not be practical for all IoT applications. While software-based solutions such as multilevel security (MLS) and hardware-based solutions such as TPM are possible, cryptographic solutions such as TPM are also practical. However, these techniques may be subject to limitations in various complex IoT systems. Although protocols such as that proposed in [129] are used to protect the security of IoT systems, they were developed to lend off specific types of threats. Given the immutability, distributed ledger, and decentralization features of blockchain, the integrity of data in the IoT can be effectively guaranteed. In particular, once the information is registered in the block and verified by the users, it is nearly impossible for malicious users to tamper with that data [130]. On the other hand, the IoT is an exciting new frontier for the integration of private blockchain distributed ledgers to guarantee the veracity of collected data. Data from the IoT can be encrypted using smart blockchain contracts [131].