Where can I find an SSH server for my OS?

SSH is now a de facto standard for command-line oriented remote administration. Unless you are using an old OS that is no longer supported by its developer, you should be able to easily find numerous free and commercial SSH server solutions for your OS. For example, if you are using FreeBSD (http://www.freebsd.org) or Ubuntu Linux (http://www.ubuntu.com), OpenSSH (http://openssh.org) is readily available.

Do I need a separate computer or device for the sharing
gateway server?

No. You can setup your existing computer also act as a sharing gateway server. You just need to install and run SSH server software. For additional information about available SSH server software, please visit SharePlug user community site at http://shareplug.net/community.

Please note that SSH sessions are encrypted with computation intensive algorithms such as AES (http://en.wikipedia.org/wiki/Advanced_Encryption_Standard) to achieve security. Hence, if the computer used for sharing gateway is not powerful or fast enough, you may experience slow data transfer.

My sharing gateway server is behind firewall.
How can I make my server accessible from the Internet?

The sharing gateway server is a typical SSH server. So, you just need to allow the port number that your SSH server is using is opened to the Internet. The standard port number for SSH is 22.

If you are using an IP sharing router, it should have an option to make a port of its client exposed to the Internet. Such feature is found under an option category usually labeled "Virtual Server" or "Port Forwarding".

How secure is the connection created between SharePlug
and my PC?

There are two connections actually involved in accessing your data. One is from SharePlug to SSH sharing gateway, and the other is from SSH sharing gateway to your PC.

The connection between SSH sharing gateway and your PC has the same security level as the normal connection created for accessing shared folders from PC to PC, i.e., no encryption is used.

For the connection between SSH sharing gateway and SharePlug, SharePlug supports the following encryption methods:

Depending on the method preference set for your server and SharePlug, one of the above encryption methods will be used. If you wish to change the preference, please go to [ Menu ] » [ Options ] » [ SSH Options ] before starting a session.

If you wish to check the currently selected encryption method and other information, please go to [ Menu ] » [ About ] » [ Current Session ].

Do you have a version of SharePlug for Windows Mobile Standard(non-touch) devices?

No. SharePlug utilizes the network resource handling feature of Windows Mobile. Unfortunately, the current iteration of Windows Mobile (version 6.5 as of Sep/2009) does *not* include such feature for Standard(non-touch) version. As soon as this changes, we'll have a version of SharePlug released for non-touch Standard devices.

Is there a way to improve the data transfer speed?

SharePlug encrypts and protects the data it delivers. Hence, assuming the raw data connection speed is the same, you can improve the data transfer speed via SharePlug by changing the encryption and MAC algorithms ([ Menu ] » [ Options ] » [ SSH Options ]).

The following is the list of algorithms currently supported in SharePlug:
(*Every* incoming and outgoing data packet goes through at least two algorithms, one chosen from "Ciphers" and the other from "MAC(Message Authentication Code) Algorithms".)

As your choice of algorithms has a direct impact on the security of your data communication, please do your own research and configure the options based on your needs. For example, ARCFour(RC4) encryption is the fastest algorithm among the listed above, but it's not as strong as AES. Also, you may feel you must use AES with 256-bit key to be secure, but according to this article (http://www.seagate.com/staticfiles/docs/pdf/whitepaper/tp596_128-bit_versus_256_bit.pdf), AES with 128-bit key is sufficiently secure.

Please note that the data encryption and protection also happen on the server. So, if your SSH sharing gateway server is not powerful or fast enough, your data transfer speed will also suffer.