Which protocol uses TLS for encryption and can run on ports 20/21 or sometimes 989/990?

The correct choice is File Transfer Protocol Secure (FTPS) because it is an extension of FTP that implements TLS (Transport Layer Security) to provide secure connections for file transfers. FTPS can indeed operate on the traditional FTP ports, 20 and 21, as well as ports 989 and 990, which are designated for secure connections using TLS.

FTPS allows for encrypted connections, ensuring that file transfers are secure from eavesdropping and tampering while in transit. This is crucial for maintaining the confidentiality and integrity of sensitive data during transfer.

In contrast, regular FTP operates without encryption, making it less secure. Secure File Transfer Protocol (SFTP) is another secure file transfer method, but it utilizes SSH (Secure Shell) for encryption rather than TLS and operates on a different port, typically port 22. Hypertext Transfer Protocol Secure (HTTPS) is specifically for secure web communications, not file transfers, and it operates primarily on port 443. Understanding the distinctions among these protocols is vital for ensuring appropriate security measures for data transfers.