Which method is primarily used to deny unauthorized access to information derived from telecommunications systems?

Emission Security is focused on preventing unauthorized access to information that can be derived from the emanations of telecommunications systems. This method looks at the potential for information to be intercepted and reconstructed from signals or emissions unintentionally leaked from devices, systems, or communications. By addressing these vulnerabilities, Emission Security implements techniques to mitigate the risk of interception, such as shielding sensitive equipment, using specific frequency ranges that are harder to intercept, and employing secure communication protocols.

In contrast, the other methods serve different aspects of security:

• Transmission Security helps to protect data while it is being transmitted, focusing primarily on encryption and securing the transmission path but not specifically on emanations.

• Physical Security involves protecting the physical infrastructure, such as buildings and hardware, from unauthorized access but does not directly address information that can be leaked through electromagnetic emissions.

• Network Security safeguards the integrity of networks and the data traveling over them but again does not zero in on the interception of sensitive information derived from unintentional emissions.

Thus, Emission Security is uniquely qualified to address the issue of unauthorized access through emanation interception, making it the correct choice.