| Description | The Routing Protocol for Low-Power and Lossy Networks (RPL) lacks any mechanism to verify the integrity of nodes during DODAG formation, leaving it structurally vulnerable to rank manipulation and selective forwarding attacks. Existing trust-based extensions detect such attacks reactively after node admission, leaving a temporal window during which compromised nodes influence routing decisions. No prior work has operationalised a formal integrity model within an RPL objective function to enforce proactive, admission-time integrity constraints. This paper presents BTI-RPL (Biba Trust Integrity for RPL), a mechanism that integrates a trust scoring component with the Biba integrity model to enforce the ‘no write-up, no read-down’ rule during DODAG formation, preventing low-integrity nodes from influencing higher-integrity routing decisions. A dynamic trust computation function is embedded within the mechanism design; the proof-of-concept evaluation employs static trust initialisation to isolate and validate the integrity enforcement behaviour under controlled adversarial conditions. BTI-RPL was implemented in Contiki-NG and evaluated on a Cooja testbed across two deployment scales: a small-scale configuration (4 nodes, 50% malicious density) and a large-scale configuration (16 nodes, 20% malicious density). Experimental results demonstrate zero integrity violations across 4,908 parent selection evaluations in the large-scale scenario, with 100% of malicious nodes detected and rejected, a Packet Delivery Ratio of 99.96%, and memory overhead of approximately 16 KB ROM and 1.5 KB RAM per node. Under identical adversarial conditions, standard RPL achieves only 24.3% PDR; BTI-RPL achieves 88.4% whilst providing deterministic integrity guarantees that probabilistic trust mechanisms are structurally incapable of delivering. These results establish BTI-RPL as a lightweight, proactive solution for routing integrity in safety-critical IoT environments where the consequences of compromised data paths are unacceptable. |
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