[rc5] Re: One Time Pad

Mikus Grinbergs mikus at bga.com
Mon Oct 27 09:58:17 EST 1997


In article <3454B2F2.14BAEFEA at optima.mme.wsu.edu>,
Chris Grantham <casper at optima.mme.wsu.edu> wrote:
>
> Hmm. Never (No.. ever) is a strong word, and one that is frequently over
> used. Maybe you could explain to the laymen (such as myself) on the
> group what OTP is, and why it is completely secure (and maybe why we
> aren't all using it for encryption ;->  ).

The key for a One-Time-Pad is as long as the message itself.

The key is used ONLY ONE TIME !!!  That means that an attacker
can NOT "line up" encrypted strings (since each string was
encrypted with its own unique key).  It also means that EACH
possible decryption of an encrypted string is EQUALLY valid -
the attacker cannot determine which is the "real" decryption.

The key is best generated by a known-to-be-random natural process
(for instance, I believe key-generating hardware has been built
which is driven by "when alpha particles are emitted" during
radioactive decay).

The problem with One Time Pads is getting the KEY to the person who
needs it to use for decryption.  The most practical way for doing
so is by diplomatic pouch (governments) or courier (businesses).
[Writeable CD-ROMs are a godsend.  One can "package" more than 600MB
of key into something that is easily carried.]

mikus
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