Port 22 is used by SSH (Secure Shell) and by extension, SFTP (Secure File Transfer Protocol), which uses SSH to securely transfer files. Ensuring that port 22 is open on the firewall allows for encrypted transmissions, providing both security and verification. Port 21 is used by FTP, which is not secure by itself. Port 23, used by Telnet, transmits data in plaintext and is less secure than SFTP/SSH. Port 443 is commonly used by HTTPS, which is secure but meant for secure web traffic, not secure file transfer specifically.