Purloined letter style data hiding.

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Purloined letter style data hiding.

Postby Galane » June 14th, 2014, 10:20 pm

Raise your hand if you still have a computer with a floppy drive.

There's a way to double the capacity of any 1.44M disk that doesn't involve any compression or other software shenanigans - but it's not possible to access all the data all the time.

There's enough space between the tracks to record a complete second set of tracks. One way to do it is by rotating the head stepper motor just enough so the heads are properly mis-aligned just right. The problem with that is then the drive can only read and write the mis-aligned disks. But it's still neat to be able to amaze the un-clued by booting two different computers with different systems using the same floppy.

The ultimate way to do this would be by hacking the stepper motor drive to be able to do half steps and by using a hidden switch or software command, substitute the half step positions for the normal full step ones. If the hack could all be hidden inside one of the drives that has a full metal cover, it could only be discovered by taking the drive apart. For the activation switch, perhaps modify the bezel so that pressing in on one end trips a small switch.

Completely hidden and only the person who built it would know the secret to accessing grandma's fudge recipe or your password key file...

Today this would mostly be a hack to do just for the challenge of doing it, yet still useful for hiding some small amount of data where pretty much nobody would ever think of looking.

All I use floppies for now are BIOS updates and loading drivers during Windows setup for systems that insist that they must be done from a real floppy disk.
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Re: Purloined letter style data hiding.

Postby k-ww » June 16th, 2014, 9:38 am

There's a drawback to your idea -
the floppy [and other] read/write head[s] do a 'trim erase' in which they
erase the space to either side of the written track, to keep the head
[if slightly misaligned] from reading data on adjacent tracks.

This would erase the data you are trying to hide.

If you are trying to hide data in plane sight, you can fiddle the formatting
so that you have one short sector or one sector more than the formating
expects to be on the track.

Another that I have seen is using a 14.3... Mhz crystal insteac of the 16MHz
crysatl in the floppy controller - This would make a floppy written with it
unreadable to a normal controller [I have seen this method used comercially].
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Re: Purloined letter style data hiding.

Postby Galane » June 16th, 2014, 5:23 pm

I've seen this work with a drive that somehow got out of alignment just right to where it could be formatted in a good drive with a Linux boot disk and in the mal-adjusted one with a Windows 98 boot disk.

Instead of just saying it can't work. Try it.
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