What is Gray Box Testing?

Gray box testing is an application security testing technique that mixes white box and black box testing. In a white box assessment, the tester has complete internal knowledge of the system being tested (source code, design docs, etc.). A black box assessment is performed without any knowledge of the system’s internals.

Gray box testing splits the difference by providing the evaluator with partial knowledge of the system internals. For example, a gray box tester may not have complete knowledge of an application’s source code but may have partial knowledge of it and/or access to design documentation. This provides more insight than black box testing and less than a white box assessment.

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What is Gray Box Testing?

Gray Box Testing Strategy

A gray box tester has more information than in a black box testing and less than in a white box test. This is intentional and enables a gray box tester to combine the benefits of both approaches.

Gray box testing can improve upon the efficiency and test coverage of a black box assessment by making full use of the information provided. While a tester does not have full access to the application source code, they have enough knowledge and documentation to understand the core functions of the application. This makes it possible to design test cases that focus on likely functionality and security issues rather than testing blindly.

Gray box assessors have less information than in a white box test, which can improve the efficiency and realism of the test. By reducing the number of inputs to the assessment, time can be focused on active testing rather than processing and reviewing provided code and documentation. Additionally, denying assessors full knowledge of the system helps to avoid biases about how a system is designed to work as opposed to how it actually does.

Steps to Perform Gray Box Testing

A gray box assessment is a structured evaluation based on the available knowledge of the system under test. It should follow these steps:

  1. Identify inputs based on white-box and black-box testing techniques
  2. Identify the outputs that these inputs should produce based on provided documentation
  3. Identify the primary control flows that should be tested
  4. Identify important sub-functions that should receive deep-level testing
  5. Identify inputs to a sub-function
  6. Identify the outputs that the sub-function should produce for the given inputs
  7. Develop and execute a test case for this sub-function
  8. Verify that the sub-function produces the expected result for the test case
  9. Repeat steps 4-8 for all sub-functions

Gray Box Testing Techniques

Gray box testing can be performed in a few different ways, including:

  • Matrix Testing: Matrix testing focuses on the variables within a program, enumerating them, evaluating the risks that they pose, and testing that they are used correctly and efficiently.
  • Regression Testing: Code may be modified to add functionality or fix security issues. Regression testing verifies that an application still passes tests after being modified.
  • Pattern Testing: Pattern testing looks into the past of an application to identify trends that have caused defects in the past and may do so in the future. The results of these tests can be used to prevent these issues from recurring in the future.
  • Orthogonal Array Testing (OAT): OAT is used with an application that has a few, complex inputs. It uses statistics to create a set of test cases that provides good test coverage without the overhead of exhaustive testing.

Black Box vs White Box Testing vs Gray box

Black box, white box, and gray box testing provide the tester with varying levels of knowledge about the internals of the system being tested. At one extreme, white box testing provides complete access to source code and design documentation. At the other, black box testers have no internal knowledge of how the application works.

These varying levels of knowledge and access significantly impact the testing process. Some of the major differences include:

  • Test Coverage: White box testing can guarantee complete test coverage because it has full access to code, while black box testing provides no such guarantees. Gray box falls in the middle since testers can perform some test planning based on documentation but are blind to undocumented and inaccessible code paths.
  • Location in SDLC: White box testing uses source code, so it can be implemented early in CI/CD pipelines. Gray and black box testing work on running code, so they fall later in the SDLC.
  • Analysis Tools: White box testing uses static code analysis tools to analyze source code. Gray and black box testing use dynamic code analysis tools, such as vulnerability scanning, to analyze a running application.
  • Tester Mindset: White box testing comes from a developer mindset, while black box testing is performed from a user perspective. Gray box testing splits the difference, eliminating developers’ biases about how an application was designed to work but also providing access to more information than the average user has.

Check Point CRT

Check Point’s Professional Services portfolio can help to support an organization’s application security efforts. White, gray, and black box security assessments are part of Check Point’s Cybersecurity Resilience/Penetration Testing Services.

Learn more about bolstering your organization’s application security program with Check Point’s professional testing services. Also, feel free to contact us to learn more about how a tailored testing program and help to identify and correct security issues within your organization.

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