A Novel Reciprocal Signal Generating Method Based on Network Delay of Random Routing Protocols

The growing popularity of Internet of Things (IoT) devices raises significant challenges for secure key distribution in wide-area networks. Traditional solutions often face high deployment costs or distance limitations. This paper proposes a novel method that leverages the inherent reciprocity of Internet transmission delay to achieve lightweight symmetric keys distribution. The core of the method lies in the generation of reciprocal delay signals, and then in the enhancement of their randomness through randomized routing protocols and additional artificial delays. Moreover, an eavesdropping model is proposed to analyze single attackers, and a probabilistic framework is established to evaluate security limits against collusion attacks. Furthermore, error correction codes are implemented to allow the raw key to be directly used for encryption, eliminating additional communication overhead. Experimental results demonstrate a correlation coefficient of 0.97 for delay signals in a local area network (LAN), confirming strong reciprocity. On the public internet, the proposed randomness enhancement improves the entropy by 2 bits. Similarly, the correlation coefficient between signals obtained by an eavesdropper and the legitimate party in this wide-area environment ranges from 0.02 to 0.26, indicating that the method is resilient to eavesdropping. This work demonstrates the feasibility of utilizing public network characteristics for secure key distribution among wide-area terminals.