Which of the following protocols is commonly used for secure file transfer over the Internet?

SFTP, or Secure File Transfer Protocol, is specifically designed for secure file transfers over the Internet. It provides a secure channel for transferring files by encrypting both the command and data channels, which protects the files being transferred from interception or unauthorized access. This encryption ensures that sensitive information is kept safe during transit.

In contrast, HTTP is primarily used for web page access, FTP is the standard protocol for file transfers but does not provide inherent security features, and SMTP is utilized for email transmission but is not intended for file transfers. Therefore, SFTP is the most appropriate choice when it comes to secure file transfer requirements.