When you use CuteFTP Pro to connect securely to a server that supports SSL or TLS, the two machines pass a sequence of commands to create a secure connection. The FTP protocol definition provides at least two distinct mechanisms by which this sequence is initiated: Explicit (active) and Implicit (passive) security.
Explicit security requires that the FTP client issue a specific command to the FTP server after establishing a connection to establish the SSL link. The default FTP server port is used. This formal method is documented in RFC 2228.
Implicit security is a mechanism by which security is automatically turned on as soon as the FTP client makes a connection to an FTP server. In this case, the FTP server defines a specific port for the client (990) to be used for secure connections.
Implicit SSL is discussed in various SSL drafts but not formally adopted in an RFC. For strict compliance to standards, use the explicit method. Implicit SSL adds benefits in the form of a dedicated port strictly used for secure connections, requiring less overhead in establishing the session. There are various FTP servers that support this mode, including GlobalSCAPE’s Secure FTP Server.
The diagram below shows a SSL session using explicit security. In this picture, the two machines communicate over an Internet connection. Time is represented vertically – the first communication is from the Client to the Server (at the top of the timeline), and subsequent communication proceeds down the timeline. The breaks in the timeline represent the passage of time.
EXPLICIT SSL CONNECTION
CuteFTP Pro adheres to Internet standards for secure transfer of files over the FTP protocol. Specifically, CuteFTP Pro implements the FTP extensions documented in RFC 2228. Any FTP Server that also implements these extensions will work with CuteFTP Pro in order to ensure the encryption of your sensitive data.
GlobalSCAPE Secure FTP Server, the server-side companion to CuteFTP Pro, adheres to the RFC 2228 standard. It is also capable of Implicit SSL sessions over a dedicated port. Refer to GlobalSCAPE Secure FTP Server’s help topics for further information on configuring a secure session to a GlobalSCAPE Secure FTP Server.