forflop

#!/bin/sh
## Fancy Info Box ########################################################
# I recently bought a bunch of 3.5" floppy disks at a local thrift shop. #
# "Why?" you ask? Because most people don't have floppy disk drives      #
# these days, so it seems to me a great way to keep the backups of my    #
# most important documents private!                                      #
#                                                                        #
# Some of the floppies I bought already contained data. Out of respect   #
# for the privacy of the previous owners, I decided to do a Gutmann      #
# Method data shred on them (with a few extra passes of 0's and 1's) to  #
# ensure their data couldn't be recovered. After, I formatted them with  #
# ext4 to take advantage of filesystem-level encryption, and I had mkfs  #
# check for damage (hey, they're old, and I don't want to loose data!).  #
# From there, I setup an encrypted folder, wrote a blank file to it,     #
# filled it with 1's, then ran shred on it, literally encrypting         #
# randomly generated data to guard against data analysis (i.e. to have   #
# my actual data blend in with encrypted "background noise" to make it   #
# difficult to tell between real and fake data).                         #
#                                                                        #
# All of this resulted in quite a bit of repeating commands (I bought    #
# quite a few floppies!), so I made this script. It's meant mainly for   #
# floppies and older hard disks (Gutmann himself said the Gutmann Method #
# isn't useful for recent hard disks). As an extra layer of protection   #
# for your floppies, you can modify your floppy disk drive by swapping   #
# the connectors for the read/write heads: the floppy disk drive is too  #
# stupid to know which head is which, so by swapping the connectors you  #
# are tricking it into thinking that the top head is the bottom one and  #
# vice versa. Any floppy disk formatted in a drive modified like this    #
# show up as unformatted in an unmodified drive (and vice versa), thus   #
# tricking (most) people that wouldn't think of this into thinking that  #
# there really isn't anything stored on your floppy disks. Combine that  #
# with ext4's builtin encryption and the fact that most people can't use #
# floppies anyway, and you really have a recipe for keeping things       #
# (Oh, but if you live near me, keep an unmoddified drive around to case #
# you find one of my floppies - I don't want you looking at my stuff!)   #
#                                                                        #
# WARNING!!! DO NOT, UNDER ANY CIRCUMSTANCE, RUN THIS SCRIPT ON A FLASH- #
# BASED STORAGE DEVICE YOU ACTUALLY INTEND TO USE! SERIOUSLY, DON'T DO   #
# IT!
# Flash-based storage devices have a limited amount of writes - you WILL #
# shorten it's life quite a bit by running this script on it. PLUS! The  #
# device's builtin wear-levelling and "bad sector hiding" removes any    #
# guarantee that repeated overwriting will securely erase any data. If   #
# you really want to keep the data on your flash devices safe, set it up #
# with strong device-level encryption (crypto-luks, etc.) *before* you   #
# put anything private on it. 256-bit AES encryption seems like a good   #
# bet. Use something stronger if it's available by the time you read     #
# this.                                                                  #
##########################################################################

mnt=/mnt
dev=/dev/sdb
datadir="${mnt}/Documents"

## Data erasing ##
# Zero-fill
shred -fvzn0 /dev/sdb
# One-fill
tr '\0' '\377' < /dev/zero > /dev/sdb
sync
# Gutmann Method
shred -fvn35 /dev/sdb
# One-fill (to help cover our tracks)
tr '\0' '\377' < /dev/zero > /dev/sdb
sync
# Zero-fill (to help cover our tracks)
shred -fvzn0 /dev/sdb
## Formatting ##
# -b4096          - ext4 requires a block size of 4096 for encryption
# -cc             - try really hard to find damaged sectors so we don't
#                   loose data
# -O ^has_journal - floppy disks don't have much space and we are loosing
#                   a bit with the large block size. Disabling journal to
#                   save on space
# -O encrypt      - tell the mkfs utility we intend to use filesystem-
#                   level encryption
mkfs.ext4 -b4096 -cc -O ^has_journal -O encrypt "${dev}"
## Set up encryption ##
# Mount the disk
mount "${dev}" "${mnt}"
# Make a folder to store encrypted data in
mkdir "${datadir}"
# Ask for a passphrase for ext4's encryption
e4crypt add_key
# Ask the user to enter the session key given by e4crypt
read -p "Enter the session key: " sesskey
# Use the session key to encrypt the data folder
e4crypt set_policy "${sesskey}" "${datadir}"
# Create a blank file, fill it with 1's. We aren't working at the block
#level here, so we need to call `sync` both times.
dd if=/dev/zero of="${datadir}/FFFFFFFF"
sync
tr '\0' '\377' < /dev/zero > "${datadir}/FFFFFFFF"
sync
# Shred & remove the file created above. Since we are doing this in the
# encrypted folder, ext4 will actually encrypt the random data being
# written to the file, creating some 'background noise' that should
# blend in seemlessly with our real data.
shred -fuv "${datadir}/FFFFFFFF"
## Fin ##
umount "${mnt}"