Distributed cryptography has scalable and robust key distribution systems which are resource and adversarial bound. Some of the complex combinatorial constructions of powerful key distribution schemes with incidence relations and algebraic constructions are suggested in this article. The proposed structure allocates node-key with combinatorial designs, which ensure deterministic connectivity and are also limited by small key storage overhead. Lightweight key agreement protocol is an extension of common combinatorial structures that are used to ensure secure pairwise communication without unnecessary exposure. The scheme is experimented with various network scale and attack conditions, demonstrating that the resilience to node capture and compromise effects is reduced by 28.6% than random redistribution of keys. The connectivity reliability is improved by 19.3% and the storage efficiency reduced by 22.4%. Positive secrecy guarantees and scale are validated through analysis and simulations. One of the contributions is the coalescence of the combinatorics theory with the realistic distributed security demands to enable effective and robust cryptography implementation.