Cross Domain Solutions and Data Diodes for Defence and Critical Infrastructure

4Secure has operated since 2003 as a UK-based specialist in secure information exchange between networks of differing trust and classification levels. Its customers sit in defence, government, and critical national infrastructure, where operational technology and enterprise IT must share data without collapsing into a single attack surface. Alongside products, the company sells consultancy on cybersecurity best practice and certification, and frames its mission around turning security controls into operational advantage rather than pure constraint.

At the core of the offering is TrustedFilter, a secure-by-design software suite that normalises, inspects, and verifies data at content level before it crosses a boundary. Structured formats such as XML and JSON are validated against syntactic and semantic schema rules, files pass through content disarm and reconstruction plus anti-virus scanning, and non-compliant data is quarantined. Modules handle high-throughput unidirectional import, bi-directional request-response using two physically separate appliances with TLS terminated for payload inspection, and real-time video or screen replication.

Hardware data diodes complement the software layer, enforcing one-way flow at the physical level so reverse communication is impossible rather than merely policy-blocked, with proxying and tunnelling for OT protocols including OPC-UA and MQTT. Market positioning leans on sovereignty: domestic engineering, a transparent supply chain, and lifecycle support intended to shorten accreditation. Published credentials include Cyber Essentials, ISO 27001, and IASME Cyber Assurance, Crown Commercial Service supplier status, and stated alignment with NIS2 and UK CNI frameworks.