Arqit NetworkSecure is a lightweight software application designed to harden VPN communications against man-in-the-middle (MITM) attacks and Store Now, Decrypt Later (SNDL) quantum attacks. It integrates with existing network infrastructure as an overlay, requiring no rip-and-replace of existing systems. NetworkSecure provides on-demand quantum-safe encryption keys brokered by Arqit's key orchestration platform. These keys are consumed by network devices to add an additional encryption layer protecting data in transit against PKI-related attacks and quantum threats, both of which exploit weaknesses in public key cryptography. The solution operates across multiple OSI stack layers: TLS (application layer), Layer 3 IPsec VPNs, Layer 2 MACsec, and Layer 1 OTNsec. It supports multiple network topologies including point-to-point, hub-and-spoke, and mesh, scaling to thousands of devices. NetworkSecure conforms to NIST cryptographic standards (e.g., AES-256, NIST ML-KEM), FIPS 140-3, NSM-10, and NSA CSfC Symmetric Key Management Requirements. It employs standard ETSI 014, Cisco SKIP, and strongSwan vici key interfaces, and is compatible with RFC 8784. Key security properties include split-trust key agreement, short-lived forward-secrecy authentication keys, data key rotation, and strong continuous authentication. It supports dynamic pre-shared keys as recommended by NSA for quantum threat protection. Management is handled through a cloud console supporting endpoint logical grouping, policy enforcement, allow/deny/quarantine controls, and log export to SIEM/XDR solutions. The solution reports negligible performance and latency impact.