The rapid evolution of Software-Defined Networking (SDN) has transformed modern communication systems by enabling centralized and adaptive control of data flows. However, the increasing dynamism of SDN environments poses new challenges to maintain data confidentiality and cryptographic integrity. This paper presents a discrete cryptographic framework for Context-Aware Packet Encryption in Active SDN Networks Using P4-Based Code Injection. The proposed model employs selective, context-driven encryption at the packet level, utilizing discrete mathematical structures to dynamically determine encryption paths and security mappings. By integrating cryptographic primitives directly within the data plane, the framework achieves fine-grained protection while reducing redundancy and latency commonly observed in network-wide encryption mechanisms. Analytical evaluation demonstrates that the proposed approach ensures robust confidentiality, efficient key utilization, and optimal resource allocation under varying network conditions. The results affirm that discrete cryptographic methods can substantially enhance the efficiency and resilience of SDN-based communication systems against evolving security threats.