The proliferation of sensor networks and other Internet of Things devices has prompted growing privacy and safety concerns. These devices have very little memory, computing power, and storage space. Security for low-powered IoT devices, such as RFID tags, nodes in wireless sensor networks (WSNs), etc., has become increasingly difficult. So, enough security for these devices was achieved by the development of lightweight cryptographic algorithms. In recent years, "smart cities" have emerged to improve contemporary lifestyles and further social development. These are enabled by developments in ICT and may open up new avenues for social and economic development. However, not everything is as secure and private as we hope it will be. The effects of the Internet of Things on IoT-based data transmission networks have been the subject of extensive study over the past few decades. Due to this flaw in the authentication process, verifying the identification of such people safely is extremely difficult. The study's goal is to provide a safe authentication technique for IoT that makes use of Hybrid and Adaptive Cryptography (HAC). In this study, we focus on authentication as a potential security risk in IoT data transmission networks. The study proposes a hybrid and adaptive cryptography (HAC) approach to authentication for the Internet of Things as a means of resolving this issue. The proposed technique of cryptographic protection makes use of the exclusive-or (Ex-or) operation, a hashing function, and a hybrid encryption strategy based on the Rivest Shamir Adleman (RSA) and the Advanced Encryption Standard (AES) algorithms. The proposed solution is simple to implement while effectively overcoming the cryptographic system's constraints via a hybrid encryption mechanism. Using the Diffie-Hellman key exchange protocol, the RSA algorithm for privacy, and the SHA-1 algorithm for authenticity, this study aims to provide a unified security architecture for modern networks.