Secure Connections 

Note: 

The Clear Command channel option is only available with SSL 

connections. 

Learning about SSL 

When you use CuteFTP 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.  

E

XPLICIT 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.  

I

MPLICIT SECURITY 

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.  

Note: 

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. For more on SSL Connection 

Mechanisms, see Troubleshooting SSL Connections. 

SSL S

ESSIONS 

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 at the top of the timeline is from the Client to the Server, and subsequent 

communications proceed chronologically down the timeline. The breaks in the timeline 

represent the passage of time.  

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