php - logic behind websites like dropbox,google drive -

i creating website similar dropbox. logic behind project going create 1 table includes username , pass , unique id.

then create folder name of unique code , store particular person file video, mp3, txt in particular folder. question how restrict other users entering folder(because can access folder directly entering url)?

also suggest me if other logic more efficient.i working on mini project.

i believe google drive (and dropbox probebly too), use https behind scenes. in case need make sure php/asp files make sure logged on user can access his/her files. depends on how creating cloud platform. use scp, ssh, in case server automatically directs client command his/her own files.