Digital Selective Calling (DSC) is a technology employed for maritime communication, specifically for transmitting digital calls to nearby vessels or shore stations in emergency situations. DSC radios are typically used in conjunction with a ship's radio equipment to send emergency calls, safety calls, or other specific calls during emergencies. They enable the transmission of digital signals to specific vessels or shore stations, providing essential information such as location, vessel identity, and other critical details. In traditional DSC communication, the message transmission process is vulnerable to attacks by eavesdroppers. Unencrypted messages can be intercepted and deciphered by eavesdroppers, leading to the disclosure of communication content and the manipulation of information. Furthermore, due to the limited computational resources of DSC devices, traditional encryption algorithms may face performance and efficiency challenges in practical applications. Therefore, this paper aims to propose an RSSI-based key generation method to encrypt DSC messages and enhance communication confidentiality. This work establishes a bidirectional RSSI collection experimental platform based on DSC radios, where RSSI data is collected for subsequent processing. A sequence preprocessing method based on median filtering and wavelet transform is utilized, and the effects of several quantization encoding schemes are compared and analyzed. Additionally, a segmented key coordination method based on RS codes is proposed to address the high inconsistency rate of key material. This work explores the feasibility of employing physical layer keys in DSC radios and provides the corresponding key generation process.