How can I securely erase a file?

Question

Is there a Gem or means of securely erasing a file in Ruby? I'd like to avoid external programs that may not be present on the system.

By "secure erase" I'm referring to overwriting the file contents.

Burglary

Answer 1

If you are on *nix, a pretty good way would be to just call shred using exec/open3/open4:

`shred -fxuz #{filename}`

http://www.gnu.org/s/coreutils/manual/html_node/shred-invocation.html

Check this similar post:

Writing a file shredder in python or ruby?

Maniacal

"I'd like to avoid external programs that may not be present on the system." I assume that means one cannot assume what OS is used, but desired to run wherever Ruby runs. – Cylindroid

Answer 2

Something like this will get you started:

#!/usr/bin/env ruby

abort "Missing filename" if (ARGV.empty?)

ARGV.each do |filename|
  filesize = File.size(filename)
  [0x00, 0xff].each do |byte|
    File.open(filename, 'wb') do |fo|
      filesize.times { fo.print(byte.chr) }
    end
  end
end

It should get you close.

For more thoroughness, you could also use 0xaa and 0x55 for alternating 0 and 1 bits in the byte. Random.rand(0xff) will give you a random value from 0 to 255.

Claqueur

This is not guaranteed to actually affect the physical storage previously used for the file - the old data will likely still be on the drive, with the new data written elsewhere. – Lookeron

Answer 3

just

1. open the file
2. write some garbage at least in amount equal to current file size
3. flush() and close()
4. repeat N times, mixing garbage with zeroes and 0xff's on different passes

Apt