In amplification of TheBooBooKitty
's writeup of how to keep information off magnetic media
, and therefore unable to be caught and processed for analysis
, I present this information.
There are significant risks to using even volatile storage for computing with sensitive information.
TheBooBooKitty's idea for a computer which a) stores everything in ram or on CD and b) switches off whenever someone tampers with it relies on the technical falsity (but practical truth) that ram loses information stored on it when it is no longer being refreshed. As we shall see, prying eyes can still access information from supposedly volatile types of storage.
Every cell of RAM contains a thin oxide which forms the capacitor dielectric. Despite refinements in the processes of manufacturing electronics over the last few years, even a perfect oxide is subject to small fluctuations when an electric field is applied. Sodium is by far the most common contaminant -- it is small (and therefore mobile), found virtually everywhere, and possesses a positive charge. Changes in the oxide are in the form of impurities (sodium and dopants) migrating toward the negative pole of the electric field (positive ions being attracted to negative poles and vice versa).
Impression of the impurities is a cumulative effect in that the longer a bit is stored in RAM, the more forceful the impression on the capacitor.
A datum stored for one second probably causes no detectable change in the state of the ram, measured immediately after power loss. Storage for one minute is probably detectable and ten minutes certainly is. Time and a lack of electric field cause these changes to dissipate. Low temperatures increase the retention time of these changes; RAM stored at -60C° could have a retention time of months, while high temperatures accelerate the speed of dissipation. Dissipation of stress, when not affected by temperature, occurs at effectively the same rate as impression.
Since the data forms a deeper impression the longer it is held in RAM, rapid rewriting of new information over old information is ineffectual for obliterating long-stored information from RAM.
The solution to this conundrum of the paranoid is therefore rapid flipping of data. Leaving data alone for less than one second should be sufficient to leave no discernable trace of sensitive data. In modern operating systems, this rapid, constant access also has the added side effect of ensuring that the data never is paged to disk.
And any thanks to everyone who's helped me correct the errors with this writeup.