SecureBlackbox 16: How can I debug SFTP client code without having an SFTP server?

You must have an SFTP server. If you don't want to use a production server or the server is not under your complete control, you can install a local SSH/SFTP server. The most obvious (but not simple) choice is OpenSSH server. You can download its port for Windows from the copSSH page. OpenSSH is free and relatively easy to configure (remember to read the manuals!). However, copSSH has big problems when running on Windows Server operating systems, and key-based authentication seems to not work at all.

Another option is taking some commercial SSH or FTP server (ensure that they include support for SFTP). Internally we use Bitvise WinSSHD. VShell is another good server; however, it's much more expensive than Bitvise (and Bitvise has a free personal license).

We strongly discourage the use of FreeSSHd, which has bugs in SSH protocol compliance, and those bugs can confuse you, making you think that it's SecureBlackbox that isn't functioning properly.