This paper presents a comprehensive survey on IoT security, focusing on application areas, security threats, and solution architectures. The Internet of Things (IoT) is the next era of communication, enabling physical objects to create, receive, and exchange data seamlessly. IoT applications aim to automate tasks and empower inanimate objects to act without human intervention. However, the rapid growth of IoT applications has raised significant security and privacy concerns. These applications require high levels of security, privacy, authentication, and resilience to attacks. The paper discusses the security challenges in IoT applications and presents four major classes of security solutions: blockchain, fog computing, machine learning, and edge computing. The paper also highlights the security issues in different layers of IoT systems, including the sensing layer, network layer, middleware layer, gateway layer, and application layer. Each layer has unique security challenges, such as node capturing, malicious code injection, false data injection, side-channel attacks, phishing attacks, access attacks, DDoS attacks, data transit attacks, routing attacks, man-in-the-middle attacks, SQL injection attacks, signature wrapping attacks, cloud malware injection, flooding attacks, secure on-boarding, extra interfaces, end-to-end encryption, firmware updates, data theft, access control attacks, service interruption attacks, malicious code injection attacks, sniffing attacks, and reprogramming attacks. The paper also discusses the improvements and enhancements required for upcoming IoT applications, including the need for rigorous penetration testing, encryption techniques, authentication protocols, scalability of security frameworks, secure data transmission, cost and capacity constraints, decentralized approaches, cloud security, data validation mechanisms, and the use of AI-based techniques for securing IoT devices. The paper concludes that blockchain technology offers a promising solution for securing IoT data due to its distributed, decentralized, and shared ledger characteristics. Blockchain can store data securely, prevent data loss and spoofing attacks, and prevent unauthorized access. The paper also discusses the benefits of blockchain in IoT applications, including secure data storage, data encryption, and prevention of data tampering. The paper concludes that blockchain, fog computing, machine learning, and edge computing are important technologies for securing IoT applications.This paper presents a comprehensive survey on IoT security, focusing on application areas, security threats, and solution architectures. The Internet of Things (IoT) is the next era of communication, enabling physical objects to create, receive, and exchange data seamlessly. IoT applications aim to automate tasks and empower inanimate objects to act without human intervention. However, the rapid growth of IoT applications has raised significant security and privacy concerns. These applications require high levels of security, privacy, authentication, and resilience to attacks. The paper discusses the security challenges in IoT applications and presents four major classes of security solutions: blockchain, fog computing, machine learning, and edge computing. The paper also highlights the security issues in different layers of IoT systems, including the sensing layer, network layer, middleware layer, gateway layer, and application layer. Each layer has unique security challenges, such as node capturing, malicious code injection, false data injection, side-channel attacks, phishing attacks, access attacks, DDoS attacks, data transit attacks, routing attacks, man-in-the-middle attacks, SQL injection attacks, signature wrapping attacks, cloud malware injection, flooding attacks, secure on-boarding, extra interfaces, end-to-end encryption, firmware updates, data theft, access control attacks, service interruption attacks, malicious code injection attacks, sniffing attacks, and reprogramming attacks. The paper also discusses the improvements and enhancements required for upcoming IoT applications, including the need for rigorous penetration testing, encryption techniques, authentication protocols, scalability of security frameworks, secure data transmission, cost and capacity constraints, decentralized approaches, cloud security, data validation mechanisms, and the use of AI-based techniques for securing IoT devices. The paper concludes that blockchain technology offers a promising solution for securing IoT data due to its distributed, decentralized, and shared ledger characteristics. Blockchain can store data securely, prevent data loss and spoofing attacks, and prevent unauthorized access. The paper also discusses the benefits of blockchain in IoT applications, including secure data storage, data encryption, and prevention of data tampering. The paper concludes that blockchain, fog computing, machine learning, and edge computing are important technologies for securing IoT applications.