Appendix C: Challenges to Implementing Federal-Wide Perimeter-Based Security

Today, the Federal Government applies a defense-in-depth strategy to protect its systems that includes agency and DHS-provided protections at various levels. But, at the same time, Government-wide programs overly rely on a perimeter-based security model to protect the Government’s networks and information systems. This model, formalized in OMB Memorandum M-08-05, Implementation of Trusted Internet Connections (TIC), focuses on standardizing security at the network boundary through consolidation of external access points. Under this model, the Government has required agencies to reduce external connections, to a target of 50, and route their traffic through this limited number of secure gateways. These gateways apply common intrusion detection and prevention capabilities under DHS’s National Cybersecurity Protection System (NCPS). NCPS consists of three sensor capabilities (collectively referred to as EINSTEIN), as well as a set of analytic tools used by cyber analysts to find, identify and categorize cyber threat activity. 1

The NCPS sensor suite is deployed in three iterations: EINSTEIN 1 (E1), which captures and analyzes network flow information; EINSTEIN 2 (E2), which incorporates intrusion detection technology that scans the content of network communications to identify and alert to known indications of malicious activity; and EINSTEIN 3-Accelerated (E3A), which detects and blocks malicious activity through DNS sinkholing and email filtering.

This perimeter-based architecture has created several challenges, specifically regarding adoption of commercial cloud and mobile technologies. Additionally, signature-based detection and protections systems provide value, but are not enough to combat the full spectrum of advanced persistent threats that rapidly change attack vectors, tactics, techniques, and procedures.2 3 All of these challenges are acknowledged and understood by DHS, and efforts are underway to address these specific issues.

As an overarching effort, DHS has undertaken a cybersecurity architectural review of Federal, Civilian, and Executive Branch infrastructure to capture empirical data, which will be used to determine the efficacy of individual and collective groupings of capabilities against specific threats to that architecture. This data will then be used to guide the evolution of DHS cyber program capabilities, to include NCPS and the CDM program.

In addition to the holistic architecture review, DHS has continuously assessed its programs to determine if the program investments they are making are appropriate. As part of this continuous assessment, DHS has identified several challenges that must be addressed to improve and deliver value to its Federal Executive Branch stakeholder community. These challenges include:

  1. Cloud Security and Situational Awareness
  2. Encrypted Network Traffic
  3. Overreliance on Static Signatures
  4. Use and Value of Classified Indicators

Cloud Security and Situational Awareness

Federal agencies have started to embrace the use of cloud services to include Infrastructure as a service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS), which has the promise to move much of the Federal Executive Branch’s computing and data to commercially available cloud environments, outside of traditional network boundaries. In doing so, the emphasis on protecting and monitoring perimeter connections of trusted networks at a limited number of physical TIC access points has introduced performance degradation. This has discouraged agencies from fully adopting cloud services, and undermines many of their key benefits such as reducing costs, flexibility, time-to-deploy, and availability and reliability. An example of a current network routing challenge for agencies that have adopted cloud services is an agency that has implemented a public-facing web service must route user traffic through a limited number of physical TIC access points for inspection, which in turn introduces latency. The diagram below illustrates how this approach is currently implemented, in a phenomenon known as “the network trombone,” which constrains the benefits of cloud services by forcing users to route traffic through a physical network location rather than being able to connect directly to the cloud service.

To address this situation, DHS has engaged with three large cloud service providers to determine how DHS may gain the insight and situational awareness from within the cloud that is similar to the information that is gained from its E1 and E2 sensors that are deployed at the TICs. The focus of this engagement thus far has been the collection of internal cloud log data, specific to the agency application and data that could be fed back to DHS to provide a similar level of situational awareness to DHS cyber analysts.

ATC Networks - TIC Trombone.png

Encrypted Network Traffic

As the use of cloud and web services continues to expand, so has the use of network transport security in the form of encrypted tunnels between end users and their applications and data. The use of transport encryption is critical for secure communications, but limits what is visible to a perimeter-based monitoring system such as E1 or E2. The amount of network traffic that is encrypted that passes through E1 and E2 sensors has increased over time, with 47 percent of all traffic being encrypted as of December 2016. This continued growth of encrypted network traffic has limited the functionality and usefulness of E1 and E2 sensors and has made it difficult for DHS to inspect this traffic for cyber threats. For DHS E2 sensors, this means that DHS signatures are unable to inspect the content of network communications and alert on malicious content.

Continued growth in encryption is both beneficial and inevitable, and DHS has commissioned research to determine potential architectural, technical, and policy mitigation strategies that could provide DHS with both the protection and situational awareness for encrypted traffic. Some of the mitigation strategies currently under evaluation include:

  1. Sensor Placement. This involves relocating the E1 and E2 sensors where the traffic is decrypted (e.g., endpoints of an encrypted tunnel). In the cases of virtual private network tunnels, one could place sensors outside of encrypted areas. For cloud environments, investigation is needed to determine how these sensors could be virtualized and placed in physical or virtual locations where Government applications and data exist.

  2. Man-In-The-Middle (MITM) Interception. This involves deploying MITM technologies that decrypt traffic, inspect it, and re-encrypt it, by placing a proxy along the network path. This proxy falsely pretends to each side to be the other side of the communications. Network proxies that intercept Transport Layer Security (TLS) traffic via MITM are commercially available. Usually this requires local clients to have blanket trust of this proxy.

  3. Key Escrow. This involves gaining access to decryption keys (e.g., as part of a broader certificate management system and architecture). A key escrow approach requires clients to register keys with a trusted third party.

Overreliance on Static Signatures

The use of signatures, or software code that inspects network traffic to look for known content, ports, and protocols, has been a fundamental part of cybersecurity practice. Similar to how anti-virus software works, intrusion detection and prevention technologies inspect traffic to look for matches against signatures of known malicious content or behavior. Although signature-based technology is widely accepted as an effective and necessary piece of cyber defense, it is not enough to protect against the most advanced and persistent threats facing the Government today. NCPS uses signatures within their E2 intrusion detection and E3A prevention capability areas. In recognition of the limitations of signature-only systems, DHS has been piloting an anomalous analytics capability that leverages artificial intelligence to detect malicious activity across networks that will allow DHS to both respond to previously unidentified incidents. DHS can then rapidly generate new signatures for both EINSTEIN sensors and agency defenses to protect the Government from those threats. DHS has seen some early success from this pilot and is planning to build a production-grade system that could be deployed at various points across the .gov architecture, both inside and outside agency network and computing enclaves.

Use and Value of Classified Indicators

The use of signatures in intrusion detection and prevention systems are based on pieces of information known as cyber threat indicators. These “indicators” can be any piece of observable information about the network traffic such as an Internet Protocol (IP) address, domain name, or file hash, that may indicate whether the traffic entering or exiting a network may be suspicious or malicious. DHS sources its indicators from multiple sources to include in-house analysis of Government traffic, commercial and open-source cyber threat data, and the intelligence community. Although all of the signatures within the E2 system are unclassified, significant portions of the signatures in the E3A intrusion prevention capability are classified. The use of classified indicators and signatures within the E3A system has been a long-standing challenge for the NCPS program because of the unprecedented way in which classified information is placed on unclassified networks for the purposes of protecting unclassified .gov network traffic. The continued use of classified information in E3A has been recognized as a cost and schedule driver, as well as limiting the range of technical capabilities available. Moreover, the use of classified information has limited the ability of DHS to engage and communicate with the agencies it helps to protect because not all agencies have personnel with the appropriate security clearances to discuss the indicators or the alerts that are generated by the system. To address this issue, DHS has commissioned a study to understand the value of using classified indicators within E3A to determine if their use should be continued, or if DHS and the agencies would be better served by using only unclassified information.

  1. See Footnote 9. 

  2. DHS Office of the Inspector General, Implementation Status of EINSTEIN 3 Accelerated. March 2014. 

  3. U.S. Government Accountability Office, Report 16-294, DHS Needs to Enhance Capabilities, Improve Planning, and Support Greater Adoption of its NCPS. January 2016.