Ensuring the confidentiality of transmitted information is crucial to protect data from unauthorized access during transmission. Here ' s an analysis of the provided options:

A. Firewall:

A firewall monitors and controls incoming and outgoing network traffic based on predetermined security rules. While it helps prevent unauthorized access to or from a private network, it doesn ' t encrypt the data being transmitted. Therefore, it doesn ' t ensure the confidentiality of the data during transmission.

B. Antivirus Software:

Antivirus software is designed to detect, prevent, and remove malicious software. It protects the system from malware but doesn ' t play a role in securing the confidentiality of data during transmission.

C. Passwords:

Passwords are used to authenticate users and control access to systems and data. While they help ensure that only authorized users can access certain information, they don ' t protect data during transmission from interception or eavesdropping.

D. Encryption:

Encryption involves converting plaintext data into a coded form (ciphertext) that is unreadable to unauthorized parties. Only those possessing the correct decryption key can convert the data back into its original form. By encrypting data before transmission, even if the data is intercepted, it remains unintelligible without the decryption key, thereby ensuring confidentiality. Encryption is widely recognized as one of the most effective methods for protecting data confidentiality during transmission.

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In conclusion, among the options provided, encryption is the most effective control for ensuring the confidentiality of transmitted information, making option D the correct answer.