thoughts on one time pads

Jonathan Thornburg jthorn at
Fri Jan 27 05:13:43 EST 2006

Two other problems with using a CD for OTP key material:

1. How to insure physical security for the N years between when you
exchange CDs and the use of a given chunk of keying material?  The
"single CD" system is "brittle" -- a single black-bag burglary to
copy the CD, and poof, the adversary has all your keys for the next
N years.

2. How to securely destroy it after use, to prevent retrospective
dumpster-diving?  Nothing short of physical destruction will stop a
determined adversary... and physical destruction is *hard*:

Smashing the CD with a hammer leaves individual fragments which can
still be read with a microscope.  (That would yield "some" key bits;
a serious adversary could "drag" these across archived encrypted-traffic
to find the position which decrypts to something that's statistically

Melting the CD should work... but in practice that takes a specialized
"oven" (I seriously doubt my home oven gets hot enough), and is likely
to produce toxic fumes, and leave behind a sticky mess (stuck to the
surface of the specialized oven).


-- Jonathan Thornburg <jthorn at>
    Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
    Golm, Germany, "Old Europe"
    "Washing one's hands of the conflict between the powerful and the
     powerless means to side with the powerful, not to be neutral."
                                       -- quote by Freire / poster by Oxfam

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