Script to download files from SSH Server

Question

Is it possible to create a script that follow the same commands FileZilla executes when connecting to an ssh server?

When I login manually using FileZilla I get the following message for the following connection types:

The server's host key is unknown. You have no guarantee that the server is the
computer you think it is.


    Host:  securedomain_1.com:22
    Fingerprint: ssh-dss 1024 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx

    Host:  securedomain_2.com:22
    Fingerprint: ssh-rsa 1024 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx

    Host:  securedomain_3.com:22
    Fingerprint: ssh-rsa 2048 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx


Trust this host and carry on connecting?
[ ] Always trust this host, add this key to the cache.
[OK] [CANCEL]

I click OK and DO NOT add key to cache...

When I login manually, these are the commands FileZilla executes:

Status: Connecting to my.secure.site.com...
Response:   fzSftp started
Command:    open "[e-mail]" 22
    [asks for key...]
    [I manually click OK]
Command:    Trust new Hostkey: Once
Command:    Pass: ********
Status: Connected to my.secure.site.com
Status: Retrieving directory listing...
Command:    cd "/SFTP/DIR"
Response:   New directory is: "/SFTP/DIR"
Command:    ls
Status: Listing directory /SFTP/DIR
Status: Calculating timezone offset of server...
Command:    mtime "IN"
Response:   1412312345
Status: Timezone offsets: Server: -18000 seconds. Local: -18000 seconds. Difference: 0 seconds.
Status: Directory listing successful

What exactly is happening when I click OK to "Trust this host and carry on connecting"?

Am I accepting a key from the SSH server?

This would be for a Windows machine. I was thinking of using WinSCP but I would like to understand what is happening when I connect to these servers. I have a few scripts that are meant for FTPS that do not work when for these servers.

Answer 1

When connecting to an SSH server, you need to verify that you trust the server's host key. This is to prevent a man-in-the-middle attack.

In WinSCP scripting, you verify the host key using the -hostkey switch of the open command.

open sftp://user:[e-mail]/ -hostkey="ssh-dss 2048 xx..."

References: Where do I get SSH host key fingerprint to authorize the server?

There's a guide how to convert Windows FTP script to WinSCP SFTP script.

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Note regarding the commands in FileZilla log: These commands are proprietary commands of the psftp (what FileZilla uses internally to implement SFTP protocol). They have nothing to do with the SFTP or the SSH protocols as such. Obviously they all map internally to some SFTP requests and you can emulate them all using WinSCP scripting. But the WinSCP commands would be different. Also note that the SFTP, contrary to the FTP, is a binary protocol, so there are no text commands like in the FTP (cd, pwd, etc.)