SUMMARY: Not-so-volatile volatile memory

[Timothy C. May]

At 9:54 AM 9/5/95, Anonymous wrote:
>> -- Summary: Data retention in semiconductor memory --
>>
>> Contrary to conventional wisdom, "volatile" semiconductor memory
>> does not entirely lose its contents when power is removed.  Both
>> static (SRAM) and dynamic (DRAM) memory retain some information on
>> the data stored in it while power was still applied.  SRAM is
>> particularly susceptible to this problem, as storing the same data
>> in it over a long period of time has the effect of altering the
>> preferred power-up state to the state which was stored when power
>> was removed.  Older SRAM chips could often "remember" the previously
>> held state for several days.  In fact, it is possible to manufacture
>> SRAM's which always have a certain state on power-up, but which can
>> be overwritten later on - a kind of "writeable ROM".
>
>Is this a new discovery?  When I used to work with DOD classified
>data, not so long ago, disk drives had to be declassified using an
>approved program, such as Norton Utilities' "WIPEINFO".  (That was
>approved up through the SECRET/SAR level, anyway.  I don't know
>about TS/SCI/SI.)  But those same regulations said that RAM was
>considered declassified within a certain time (30 seconds, I think)
>after power was removed.  (That time figure was UNclassified, BTW.)
>I think it was just to allow time for the voltage to bleed off of
>the power supply's filter capacitors, and not related to the
>relative volatility of DRAM.

The Gutman article was discussing residual/remnant storage a lot more
subtle than the usual "bleed-off" charateristics.

One interesting twist is using radiation sources to "snapshot" or "freeze"
the internal contents of dynamic RAM.

I worked with DRAMs for more than a decade at Intel, though never on this
particular issue. But I read a lot of the public papers on radiation
effects on DRAMS, including the "freezing" of data patterns into DRAMs by
exposure.

(I recall thinking at the time, circa 1980, that someday raids on computers
could involve bringing in flash radiation sources to "snapshot" the
contents of DRAM.)

Sandia Labs did a lot of the work on  this, and results are reported at the
annual Nuclear and Space Radiation Effects Conference. The December issue
of "IEEE Transactions on Nuclear Science" every year includes the
proceedings of this conference. Any large university library should have
it.

It's also possible to literally freeze a DRAM--with "Arctic Freeze" spray,
for example--and stop the self-discharge of DRAM cells.

I doubt any of these efforts are being used, though. Looking at how raided
computers are simply carted off in the backs of pickup trucks, with disk
drives thrown in with monitors, I suspect nothing this sophisticated has
ever been tried. Quantico might have some more sophisticated approaches,
but they're not publically discussing them.

---------:---------:---------:---------:---------:---------:---------:----
Timothy C. May              | Crypto Anarchy: encryption, digital money,
tcmay at got.net  408-728-0152 | anonymous networks, digital pseudonyms, zero
Corralitos, CA              | knowledge, reputations, information markets,
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