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A cross-domain solution (CDS) is a means of information assurance that provides the ability to manually or automatically access or transfer information between two or more differing security domains. They are integrated systems of hardware and software that enable transfer of information among incompatible security domains or levels of classification. Modern military, intelligence, and law enforcement operations critically depend on timely sharing of information. CDS is distinct from the more rigorous approaches, because it supports transfer that would otherwise be precluded by established models of computer, network, and data security, e.g., Bell–LaPadula model and Clark–Wilson model. CDS development, assessment, and deployment are based on risk management.
The goal of a CDS is to allow an isolated critical network to exchange information with others, without introducing the security threat that normally comes from network connectivity.
The three primary elements demanded from cross domain solutions are:
- Data confidentiality; most often imposed by hardware-enforced one-way data transfer
- Data integrity: content management using filtering for viruses and malware; content examination utilities; in high-to-low security transfer audited human review
- Data availability: security-hardened operating systems, role-based administration access, redundant hardware, etc.
The acceptance criteria for information transfer across domains may be simple (e.g. antivirus scanning before transfer from low to high security domains) or complex (e.g. multiple human reviewers must examine and approve a document before release from a high security domain). One-way data transfer systems (one-way traffic systems, data diodes), are often used to move information from low security domains to secret enclaves while assuring that information cannot escape. Cross-domain solutions often include a High Assurance Guard.
In previous decades, multilevel security (MLS) technologies were developed and implemented that enabled objective and deterministic security, but left little wiggle room for subjective and discretionary interpretation. These enforced mandatory access control (MAC) with near certainty. This rigidity prevented simpler solutions that would seem acceptable on the surface. Automated information systems have enabled extensive information sharing that is sometimes contrary to the need to avoid sharing secrets with adversaries. The need for information sharing has led to the need to depart from the rigidity of MAC in favor of balancing need to protect with need to share. When the ‘balance’ is decided at the discretion of users, the access control is called discretionary access control (DAC) that is more tolerant of actions that manage risk where MAC requires risk avoidance. Allowing users and systems to manage the risk of sharing information is in some way contrary to the original motivation for MAC.
The unintended consequences of sharing can be complex to analyze and should not necessarily be left to the discretion of users who may have a narrow focus on their own critical need. These documents provide standards guidance on risk management:
- "Recommended Security Controls for Federal Information Systems & Organizations". Computer Security Division - Computer Security Resource Center. National Institute of Standards and Technology (NIST). 2011-11-16., SP 800-53 Rev3
- "Security Categorization and Control Selection for National Security Systems" (PDF). The Committee on National Security Systems (CNSS)., Instruction No. 1253
- "Cross Domain Enterprise Service (CDES)". Information Assurance Support Environment. Defense Information Systems Agency (DISA). 2011-11-16. Archived from the original on 2008-03-26. Retrieved 2012-01-16.
- "Cloud Computing Strategy" (PDF). DTIC.MIL.
- Aristotle, Jacob. Cross-Domain Solution.
- "Cross Domain Solutions". Deep-Secure.
- "Cross Domain Solutions - Ensuring Complete Data Security".
- "Nexor Data Diode". Nexor. Retrieved 3 June 2013.
- "Dual Data Diode Information Transfer Products". Owl Computing Technologies, Inc. Retrieved 2012-01-16.
Unified Cross Domain Management Office (UCDMO), Cross Domain Overlay, 1 December 2011, ver 1.0; provides extensive security control guidance to implement CDS platform address security controls for hardware and software, enforced with advanced inspections.
- Rockwell Collins High Assurance Cross Domain Solutions
-  BAE Systems Cross Domain Solutions
- CJCSI 6211.02D, Defense Information System Network (DISN) Responsibilities. s
- Forcepoint - Trusted Gateway System
- Embvue ISIS Cross Domain Secure Networking Solutions
- Advatech Pacific - Tactical Cross Domain Solution
- Braxton Cross-Domain Data Dissemination
- Nexor Cross Domain Solutions
- Tresys XD Bridge™ Cross Domain Solution
- Tresys XD Air™ Removable Media Threat Protection
- Tresys XD Guardian™ Cross Domain Guard for Non-U.S Networks