What can I do to replace FTP?

I'd like to replace FTP access with systems that are more secure. Sending passwords in plain text with no encryption is unacceptable and with single-sign-on growing, becoming less acceptable daily.

The catch: I need something that supports Linux, Windows and OS X and the server needs to run on Windows.

Edit: It also needs to authenticate users against pre existing Windows credentials.

Solution 1:

One option is to use webdav. IIS supports webdav. Since you need the system to be secure you will obviously want to setup SSL.

Webdav is usually going to be open through most firewalls and will operate through a standard http proxy. Most of the other options suggested tend to be more difficult to get through firewalls that you don't control.

OSX, and Windows have native webdav clients. Linux can use webdav via fusedav.

Webdav is probably going to be somewhat easier for you users, but it does act somewhat quirky on occasion.

Solution 2:

SFTP sounds like what you need, and OpenSSH runs just fine under Windows/Cygwin, with clients available for all the platforms you need.

Solution 3:

FTPS would also work.

http://en.wikipedia.org/wiki/FTPS

Josh