Question

What are covert channels? Give an example of a covert channel.

Short answer

A covert channel is a type of communication that enables information transfer that can potentially violate a system's security policies. An example of covert channels can be the use of a shared resource (like the wallpaper color in a multi-user OS) where changes in the resource's state can be used to convey information.

Step-by-step solution

Defining Covert Channel

Covert channels are a type of communication pathway that enables two parties to exchange information in a way that violates the system's security policies. This type of communication is usually done in a concealed or 'covert' way which is not designed to be used for communication, making it challenging for system administrators to detect.

Understanding Covert Channels

Covert channels can be divided into two types: storage channels and timing channels. Storage channels involve the direct or indirect writing of a storage location by one process and the direct or indirect reading of the storage location by another process. Timing channels involve one process signaling information to another by modulating its own use of system resources (like CPU time) in a way that affects the real response time observed by the second process.

Example of a Covert Channel

Let's look at an example of a storage covert channel: Consider a multi-user operating system where the color of the wallpaper is visible to all users. If one user (the sender) changes the color of the wallpaper, the other user (the receiver) can see the change. This method can be used to send binary messages: for example, a red wallpaper could represent '1' and a blue wallpaper could represent '0'. This information exchange is a form of a covert channel since it's carrying on without the system administrator's knowledge and it's manipulating a feature (wallpaper color) in an unintended way to enable communication.

Key concepts

Security Policies

Security policies are crucial in maintaining the integrity and confidentiality of a system. They define rules and controls that govern how data and resources are managed and accessed within a computer system. These policies are designed to prevent unauthorized access, alterations, and data leakage, ensuring that sensitive information remains protected.

• Access Control: Determines who is allowed to access or modify data.
• Data Protection: Ensures that data remains confidential and unaltered.
• Accountability: Keeps track of who accessed what data and when.

Security policies strive to delineate clear barriers against any unauthorized use. However, covert channels challenge these barriers by enabling communication through unintended pathways that these policies might not anticipate.

Communication Pathways

Communication pathways refer to the routes taken for information exchange between entities within a system. Typically, these pathways are well-defined and regulated by protocols and security measures. However, covert channels exploit unconventional pathways to communicate without detection.

• Standard Pathways: These include direct communication channels such as network connections adhering to protocol standards.
• Covert Pathways: These alternative channels misuse system resources, making them difficult to detect and monitor.

Understanding the distinction between conventional pathways and covert channels is essential for creating better monitoring and detection systems that uphold security policies.

Storage Channels

Storage channels are a form of covert channel where information is transferred through shared storage mediums. This indirect method allows data exchange between processes by altering data in a way that another process can later interpret.

• Data Alteration: One process changes a data value in a storage location, such as a file, which another process can read.
• Example: Changing a system setting, like wallpaper color, to communicate binary information.

These channels exploit the fact that multiple processes can access and modify the same storage areas, facilitating communication that bypasses standard security controls.

Timing Channels

Timing channels convey information by modifying the timing of events in a way that can be detected by another party. These channels are particularly clever as they utilize the system's resource usage patterns like CPU cycles or network delays, rather than manipulating data directly.

• Resource Manipulation: A sender modulates its use of system resources to create a pattern.
• Time-Based Communication: The receiver observes the pattern in response times and decodes the message.

Timing channels can be challenging to detect due to their indirect nature. They require sophisticated monitoring systems to identify unusual patterns in timing metrics that could indicate a covert exchange of information.