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Cross-domain solution

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A cross-domain solution (CDS) is an integrated <a href="Information_assurance" title="Information assurance">information assurance</a> system composed of specialized <a href="Software" title="Software">software</a> or hardware that provides a controlled interface to manually or automatically enable and/or restrict the access or transfer of information between two or more <a href="Security_domain" title="Security domain">security domains</a> based on a predetermined security policy.<a href="#cite_note-1">[1]</a><a href="#cite_note-2">[2]</a> CDSs are designed to enforce domain separation and typically include some form of content filtering, which is used to designate information that is unauthorized for transfer between security domains or levels of classification,<a href="#cite_note-3">[3]</a> such as between different military divisions, intelligence agencies, or other operations which depend on the timely sharing of potentially sensitive information.<a href="#cite_note-4">[4]</a>

The goal of a CDS is to allow a trusted <a href="Network_domain" title="Network domain">network domain</a> to exchange information with other domains, either one-way or bi-directionally, without introducing the potential for security threats. CDS development, assessment, and deployment are based on comprehensive risk management. Every aspect of an accredited CDS is usually evaluated under what is known as a Lab-Based Security Assessment (LBSA) to reduce potential vulnerabilities and risks. The evaluation and accreditation of CDSs in the United States are primarily under the authority of the National Cross Domain Strategy and Management Office (NCDSMO) within the <a href="National_Security_Agency" title="National Security Agency">National Security Agency</a> (NSA).

CDS filter for viruses and malware; content examination utilities; in high-to-low security transfer audited human review. CDS sometimes has security-hardened operating systems, role-based administration access, redundant hardware, etc.

The acceptance criteria for information transfer across domains or <a href="Cross-domain_interoperability" title="Cross-domain interoperability">cross-domain interoperability</a> is based on the security policy implemented within the solution. This policy may be simple (e.g., <a href="Antivirus_software" title="Antivirus software">antivirus</a> scanning and <a href="Whitelisting" class="mw-redirect" title="Whitelisting">whitelist</a> (also known as an "allowlist") check before transfer between peer networks) or complex (e.g., multiple content filters and a human reviewer must examine, redact, and approve a document before release from a high-security domain<a href="#cite_note-5">[5]</a>).<a href="#cite_note-6">[6]</a> <a href="Unidirectional_network" title="Unidirectional network">Unidirectional networks</a> are often used to move information from low-security domains to secret enclaves while assuring that information cannot escape.<a href="#cite_note-7">[7]</a><a href="#cite_note-8">[8]</a> Cross-domain solutions often include a <a href="High_Assurance_Guard" class="mw-redirect" title="High Assurance Guard">High Assurance Guard</a>.

Though cross-domain solutions have, as of 2019, historically been most typical in military, intelligence, and law enforcement environments, one example is the flight control and infotainment systems on an airliner.<a href="#cite_note-9">[9]</a>

<div class="mw-heading mw-heading2"><h2 id="Types">Types</h2></div>

There are three types of cross-domain solutions (CDS). <a href="#cite_note-10">[10]</a> These types are broken down into Access, Transfer, and Multi-level solutions (MLS) and all must be included in the cross-domain baseline list before Department of Defense-specific site implementations.<a href="#cite_note-11">[11]</a> Access Solution "An access solution describes a user’s ability to view and manipulate information from domains of differing security levels and caveats. In theory, the ideal solution respects separation requirements between domains by preventing overlapping data between domains, which ensures data of different classifications cannot ‘leak’ (i.e. data spill) between networks at any host layer of the OSI/TCP model. In practice, however, data spills are an ever-present concern that system designers attempt to mitigate within acceptable risk levels. For this reason, data transfer is addressed as a separate CDS".<a href="#cite_note-:0-12">[12]</a> Transfer Solution offers the ability to move information between security domains that are of different classification level or different caveat of the same classification level. Multi-level Solutions "Access and transfer solutions rely on multiple security levels (MSL) approaches that maintain the separation of domains; this architecture is considered multiple single levels. A multi-level solution (MLS) differs from MSL architecture by storing all data in a single domain. The solution uses trusted labeling and integrated Mandatory Access Control (MAC) schema as a basis to mediate data flow and access according to user credentials and clearance to authenticate read and write privileges. In this manner, an MLS is considered an all-in-one CDS, encompassing both access and data transfer capabilities."<a href="#cite_note-:0-12">[12]</a>

<div class="mw-heading mw-heading2"><h2 id="High_Assurance_Guard">High Assurance Guard</h2></div>

A High Assurance Guard (HAG) is a <a href="Multilevel_security" title="Multilevel security">multilevel security</a> computer device which is used to communicate between different <a href="Security_domain" title="Security domain">security domains</a>, such as <a href="NIPRNet" title="NIPRNet">NIPRNet</a> to <a href="SIPRNet" title="SIPRNet">SIPRNet</a>. A HAG is one example of a <a href="Controlled_Interface" class="mw-redirect" title="Controlled Interface">Controlled Interface</a> between security levels. HAGs are approved through the <a href="Common_Criteria" title="Common Criteria">Common Criteria</a> process.

A HAG runs multiple <a href="Virtual_machine" title="Virtual machine">virtual machines</a> or physical machines - one or more subsystems for the lower classification, one (or more) subsystems for the higher classification. The hardware runs a type of <a href="Knowledge_management" title="Knowledge management">knowledge management</a> software that examines data coming out of the higher classification subsystem and rejects any data that is classified higher than the lower classification. In general, a HAG allows lower classified data that resides on a higher classified system to be moved to another lower classified system. For example, in the US, it would allow unclassified information residing on a Secret classified system to be moved to another Unclassified system. Through various rules and filters, the HAG ensures that data is of the lower classification and then allows the transfer.

On the application layer, the HAG runs an "evaluated mandatory integrity policy" that provides sensitive files, data and applications protection from inadvertent disclosure. At the operating system level, the HAG must have a multilevel kernel that ensures sensitive information, processes, and devices stored and running on the system at different sensitivity levels cannot intermingle in violation of the system's mandatory security model.

The systems are certified via the Common Criteria; depending on the classification, the system may require Common Criteria Evaluated Assurance Level (EAL) 3 or higher. For examples, in the US, an evaluation at the EAL 5 or EAL 5+ (EAL 5 Augmented) or higher is required to export from a Secret domain to an Unclassified domain.

Some manufacturers may use "Trusted Computer System" or "Trusted Applications with High Assurance" as an equivalent term to HAG.

The HAG is mostly used in email and <a href="Defense_Message_System" title="Defense Message System">DMS</a> environments as certain organizations may only have unclassified network access, and they need to send a message to an organization that has only secret network access. The HAG provides them this ability.

<div class="mw-heading mw-heading2"><h2 id="Unintended_consequences">Unintended consequences</h2></div>

In previous decades, <a href="Multilevel_security" title="Multilevel security">multilevel security</a> (MLS) technologies were developed. These enforced <a href="Mandatory_access_control" title="Mandatory access control">mandatory access control</a> (MAC) with near certainty. <a href="Automated_information_system" class="mw-redirect" title="Automated information system">Automated information systems</a> sometimes share information contrary to the need to avoid sharing secrets with adversaries. When the ‘balance’ is decided at the discretion of users, the access control is called <a href="Discretionary_access_control" title="Discretionary access control">discretionary access control</a> (DAC), that is more tolerant of actions that manage risk where MAC requires risk avoidance.

These documents provide standards guidance on risk management:

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://csrc.nist.gov/publications/PubsSPs.html">"Recommended Security Controls for Federal Information Systems & Organizations"</a>. Computer Security Division - Computer Security Resource Center. National Institute of Standards and Technology (NIST). 2011-11-16.</cite>, SP 800-53 Rev3</li>

<li><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.cnss.gov/Assets/pdf/Final_CNSSI_1253.pdf">"Security Categorization and Control Selection for National Security Systems"</a> (PDF). The Committee on National Security Systems (CNSS).</cite>, Instruction No. 1253</li></ol>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><a href="#cite_ref-1">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20080326230421/http://iase.disa.mil/cds/">"Cross Domain Enterprise Service (CDES)"</a>. Information Assurance Support Environment. Defense Information Systems Agency (DISA). 2011-11-16. Archived from <a rel="nofollow" class="external text" href="http://iase.disa.mil/cds/">the original</a> on 2008-03-26. Retrieved 2012-01-16.</cite>

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<li id="cite_note-2"><a href="#cite_ref-2">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://owlcyberdefense.com/learn-about-cross-domain-solutions/">"Learn About Cross Domain Solutions"</a>. Owl Cyber Defense. Aug 25, 2020. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200921130317/https://owlcyberdefense.com/learn-about-cross-domain-solutions/">Archived</a> from the original on 2020-09-21.</cite>

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<li id="cite_note-3"><a href="#cite_ref-3">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://apps.dtic.mil/dtic/tr/fulltext/u2/a563989.pdf">"Cloud Computing Strategy"</a> (PDF). DTIC.MIL. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160816162753/http://www.dtic.mil/dtic/tr/fulltext/u2/a563989.pdf">Archived</a> (PDF) from the original on August 16, 2016.</cite>

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<li id="cite_note-4"><a href="#cite_ref-4">^</a> <cite id="CITEREFAristotle2012" class="citation book cs1">Aristotle, Jacob (April 2012). <a rel="nofollow" class="external text" href="http://dl.acm.org/citation.cfm?id=2378462">Cross-Domain Solution</a>. Secut Press. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-613-6-31800-4</bdi>.</cite>

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<li id="cite_note-5"><a href="#cite_ref-5">^</a> Slater, T. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140714155934/http://www.ncoic.org/cross-domain-interoperability/">"Cross-Domain Interoperability"</a>, <a rel="nofollow" class="external text" href="https://web.archive.org/web/20041001032434/http://www.ncoic.org/">Network Centric Operations Industry Consortium - NCOIC</a>, 2013

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<li id="cite_note-6"><a href="#cite_ref-6">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.crossdomainsolutions.com">"Cross Domain Solutions - Ensuring Complete Data Security"</a>.</cite>

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<li id="cite_note-9"><a href="#cite_ref-9">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://interset.com/2017/01/04/can-airplane-get-hacked-probably/">"Can an Airplane Get Hacked? (Probably.)"</a>. Interset. 2017-01-04. Retrieved 2019-03-07.</cite>

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<li id="cite_note-11"><a href="#cite_ref-11">^</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://rmf.org/wp-content/uploads/2017/10/CNSSI-4009.pdf">"CNSSI-4009"</a> (PDF). RMF.org. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200228184213/https://rmf.org/wp-content/uploads/2017/10/CNSSI-4009.pdf">Archived</a> (PDF) from the original on 2020-02-28. Retrieved 28 February 2020.</cite>

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<li id="cite_note-:0-12">^ <a href="#cite_ref-:0_12-0">a</a> <a href="#cite_ref-:0_12-1">b</a> <cite id="CITEREFSmith2020" class="citation web cs1">Smith, Scott (28 February 2020). <a rel="nofollow" class="external text" href="https://www.sans.org/reading-room/whitepapers/dlp/shedding-light-cross-domain-solutions-36492">"Shedding Light on Cross Domain Solutions"</a>. SANS Institute Information Security Reading Room. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20200228184214/https://www.sans.org/reading-room/whitepapers/dlp/shedding-light-cross-domain-solutions-36492">Archived</a> from the original on 2020-02-28. Retrieved 28 February 2020.</cite>

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