Which protocol adds security by encrypting the data during file transfer?

The chosen option is the most appropriate because SFTP, which stands for Secure File Transfer Protocol, specifically incorporates encryption to protect the data being transferred. This means that the files are not only sent over a network but are also secured against unauthorized access by encrypting the information. This encryption helps to ensure that even if the data packets are intercepted during transit, they cannot easily be read or understood, providing a significant security advantage for file transfers.

In contrast, the other protocols mentioned do not include encryption as a built-in feature. HTTP, for instance, is the standard protocol for transferring web pages but does not encrypt the data during transmission, making it vulnerable to eavesdropping. FTP, while a commonly used file transfer protocol, also lacks encryption, which can expose sensitive data. SMTP, used primarily for sending emails, similarly does not include encryption by default, although extensions can be implemented to secure email transmission. Thus, SFTP stands out for its ability to securely encrypt file transfers, making it the most relevant choice for data protection during transference.