Limited user access with key control to sftp only?

view story

http://www.linuxquestions.org – Dear All, I need to give access to user to only sftp some files into a particular folder in /var/www/html/folder1. User will be highly restricted to just this folder and nothing else and also disable everything else possible. I am using key based login. So how to go about it. Must I share my key ? (HowTos)