CryptoFS is a encrypted filesystem for Filesystem in Userspace (FUSE)
and the Linux Userland FileSystem (LUFS).
CryptoFS will use a normal directory to store files encrypted. The
mountpoint will contain the decrypted files. Every file stored in
this mountpoint will be written encrypted (data and filename) to the
directory that was mounted. If you unmount the directory the encrypted
data can only be access by mounting the directory with the correct key
again. Like other FUSE/LUFS filesystems it does not need root access
or any complicated setup like creating a filesystem on a encrypted disk
using the loop device.
This requires fuse (also available at SlackBuilds.org), although it can
alternatively use LUFS if you have that installed from elsewhere.