###### Abstract  
The Internet of Things (IoT) is an integrated environment as it merges physical smart objects to the Internet via wireless technologies to share data. The global connectivity of IoT devices brings the needs to ensure security and privacy for data owners and data users. In this paper, an attribute-based access control scheme for IoT (AAC-IoT) using Hyperledger Fabric (HLF) blockchain is proposed to address the security challenges. In the AAC-IoT scheme, data owners are registered and authenticated using identities, certificates and signatures. Data users, however, are registered with identities, certificates, signatures and physical unclonable function (PUF); then a credence score is computed for users to predict the originality during authentication. For access control, attribute-based access control (ABAC) is used, and the number of attributes is selected based on the sensitivity of the data. In accordance with the attributes count, the access control policies are generated. The novel concept of attribute count is determined from a fuzzy logic method using data type and preference. Hyperledger Fabric (HLB) blockchain is presented to manage meta-data and security credentials from data owners and data users, respectively, using a lightweight hashing algorithm. The AAC-IoT model using HLF blockchain is developed with Java programming language and iFogSim simulator. The performance metrics are measured based on latency, throughput and storage overhead, and the results show better outcome than the previous research work.  
attribute based access control; authentication; Hyperledger Fabric; blockchain; Internet of Things +
Footnote †: journal: Applied Sciences  
1 Faculty of Computing and Information Technology, King Abdulaziz University, Jeddah 21589, Saudi Arabia; obamasek@kaau.  
According to the major issues in IoT, the solutions for security are cryptographic techniques, access control methods and hashing. However, there are massive numbers devices in IoT, so a distributed security environment using blockchain is presented for ensuring security [8; 9; 10; 11; 12].  
Blockchain technology yields efficient results in privacy and security. In general, the blockchain is designed as a major combination of users, regulators, ledgers, and smart contracts. The potential of blockchain is that no one can modify the contents in each block since the values are in hashes [13; 14; 15]. Artificial Intelligence (AI) methods are also incorporated into blockchain for data protection [16]. Blockchain is able to support the processes of authenticating devices, storing data, and validating access control policies [17; 18]. Access control (AC) in IoT prefers to use lightweight methods due to the low computation ability of IoT devices [19; 20; 21; 22]. AC performs authentication and authorization based on previously defined policies. Attribute-based access control (ABAC) is one of the popular AC mechanisms followed to ensure security in the designated system. The attributes in ABAC depend on the device, its characteristics and the data it collects. For instance, the attributes of a device can be identity, name, etc., In this way, values of attributes differ from device to a device.  
To improve security by ABAC, multiple attributes were taken into account, and blockchain is introduced for this process. A signature is one of the significant attributes that is unique for users, and it is verified in blockchain. In ABAC, the attributes are protected using hashing or cryptography. Since the leakage of attributes leads to access for illegitimate users, the attributes are hidden. On the other hand, the data from an owner is stored encrypted based on the data attributes. Security and privacy play a vital role in ensuring that the user's data is protected in the storage. In this paper, the provisioning of ABAC for IoT devices by using Hyperledger Fabric (HLF) blockchain is proposed. The consideration of attributes in accordance with the device and the data it produces will improve security.