Write once perpetual storage, is such a thing possible?
Is it possible, with modern, or easily foreseeable technology, to build a compact digital data storage device that cannot be erased without removing the data store? The storage in question to be used to blackbox data on a spacecraft.
Answers should use examples of any and all of:
- currently prototype systems
- existing data storage
- and/or those used historically
The aim is to have a storage system from which data, once recorded, cannot be removed without completely removing the storage core of the system, that is to say that the recording medium is physically and indelibly write only. Data cannot be overwritten or erased by the system or by outside interference and should last as long as possible at Normal Temperature and Pressure (20°C and 1 atmosphere) and 45% relative humidity. I had considered these little babies but they can not only be overwritten they can also be annealed at high temperature to erase them completely. Assume that anyone who is going to be trying to read these systems will know the encoding system used and have the technology to read them, I'm looking for an indelible record, I do realise that on any long enough time scale encoding will shift and data will become unreadable.
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1 answer
Since you say in a comment that you're willing to settle for a combination of tamper-evident and write-only unless tampered with, as opposed to strictly tamper-proof (which indeed is a much harder problem to solve)...
You could easily model this after aircraft black boxes (flight data recorders and cockpit voice recorders).
Basically, make a dead-simple recorder that meets whatever criteria you have, and make it reliable. For a long time in aviation, this was a simple recorder to magnetic or even physical storage (in the form of engraving onto a slowly moving aluminium foil), though recently manufacturers have moved to fully digital storage. Magnetic tape recording has the advantage that the tape can be made as an endless loop of basically arbitrary length, allowing recording of a known amount of data which is automatically overwritten when needed; digital storage systems would need to implement this in some other manner, but the principle can remain the same.
With the recorder in place, define a dead-simple interface to provide the data to be recorded. Don't allow any readout; for example, in the case of magnetic tape storage, you could accomplish this by physically having no playback/read head. The simplest would probably be for a n-track recorder to have n distinct analog inputs recording onto their own tracks on the storage medium.
As long as there's power, the recorder runs and records whatever is presented on the inputs.
Now apply standard tamper-evidence measures to the whole device. Seal the interior in epoxy (but make sure that it won't overheat during use), use one-way screws, apply some glitter nail polish to edges and document the resulting pattern, and whatever else might make the device more tamper-evident. Your ideas are probably as good as mine.
Next, apply tamper-evidence measures to the connections to whatever sensors feed data into the device.
If you want to go low-tech, add an old-style impact (for example, dot matrix) printer to the system and have it regularly print checksums of stored digital data along with some kind of timestamp. If there's tampering, the paper record and the digital record won't match, while the paper record doesn't need to contain all of the raw data.
None of this will prevent tampering, but it will make it a whole lot more difficult to tamper with the recorded data without there being some indications that tampering occured.
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