There are currently 18.8 billion Internet of Things (IoT) devices online worldwide. The number is expected to rise to 41 billion in 2030 due to technological advances such as 5G. Constrained Application Protocol is a very popular communication protocol specifically designed for IoT devices with lower overhead required per payload. CoAP was designed to be as lightweight as possible without any inherent security mechanisms added innately; this is due to IoT device’s resource constrained nature. This work aims to address CoAP’s vulnerabilities towards security by encrypting CoAP’s messages at the application layer using an ASCON cipher. ASCON has an Authenticated Encryption with Associated Data (AEAD) mechanism in addition to its encryption that allows it to implement the confidentiality and authenticity services of security. This work evaluates ASCON-CoAP communication in a real-world IoT setup and compares it against Datagram Transport layer Security (DTLS)-CoAP and plaintext CoAP in terms of latency, power consumption, and resistance to network-based attacks. The results obtained from Orange pi 2 W reveal that ASCON provides comparable security to DTLS while achieving lower handshake delays of 65% and 12.2% reduced energy consumption, making it suitable for scalable and secure IoT deployments.