In a wireless environment, data is transmitted over the airwaves, making it a broadcast medium inherently susceptible to eavesdropping by any unauthorized party within range. Therefore, protecting sensitive data during transmission is the most critical and fundamental security requirement. Encrypting sensitive data in transit ensures confidentiality and prevents attackers from intercepting and reading valuable information. This is the primary function of wireless security protocols like WPA2 and WPA3. While other forms of data protection are important, securing sensitive data as it travels across the wireless link is a non-negotiable first line of defense.

B. Sensitive data in memory: This is an endpoint security concern (protecting data in use), not a primary consideration for the wireless transmission path itself.

C. Non-sensitive data at rest: The classification "non-sensitive" implies that the data does not require the same stringent confidentiality controls, making its encryption a lower priority.

D. Non-sensitive data in archives: Similar to data at rest, encrypting non-sensitive archived data is a good practice but not as universally critical as protecting sensitive data in transit.

1. National Institute of Standards and Technology (NIST) Special Publication 800-97, Establishing Wireless Robust Security Networks: A Guide to IEEE 802.11i. Section 2.1, "Security Issues," highlights that wireless networks are vulnerable to passive eavesdropping attacks, and the primary countermeasure is encryption to provide confidentiality for data in transit.

2. Kurose, J. F., & Ross, K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). In Chapter 8, "Wireless and Mobile Networks," Section 8.3.3, "IEEE 802.11 Security," the text explains that protocols like WPA3 are designed specifically to provide confidentiality, authentication, and integrity for data frames transmitted over the wireless link.

3. Purdue University, College of Engineering Courseware (ECE 695), Wireless Security. Lecture materials consistently emphasize that the broadcast nature of the wireless medium necessitates strong encryption for data in transit to prevent eavesdropping, which is the most basic and prevalent threat. The need to encrypt data over the air is presented as a foundational principle of wireless security.