154 lines
5.9 KiB
Plaintext
154 lines
5.9 KiB
Plaintext
From fork-admin@xent.com Thu Oct 3 12:55:13 2002
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To: Digital Bearer Settlement List <dbs@philodox.com>, fork@spamassassin.taint.org
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From: "R. A. Hettinga" <rah@shipwright.com>
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Subject: Re: Optical analog computing?
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Date: Wed, 2 Oct 2002 16:34:21 -0400
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--- begin forwarded text
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Delivered-To: fork@spamassassin.taint.org
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To: fork@spamassassin.taint.org
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Subject: Re: Optical analog computing?
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From: Dave Long <dl@silcom.com>
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Sender: fork-admin@xent.com
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Date: Wed, 02 Oct 2002 11:09:34 -0700
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> > "the first computer to crack enigma was optical"
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>
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> Computing with interference patterns, etc, makes perfect sense, but Enigma
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> was cracked by building mechanical systems that were essentially Enigma
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> machines and brute-forcing.
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Look for "Zygalski sheets".
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By Koerner's* narrative, it wound up
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being a hybrid affair: Bletchley had
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mock Enigmas which cycled through the
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Enigma's ~18k starting positions in a
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quarter of an hour, but the Germans
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started using a plugboard which then
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had ~1.5x10^14 possibilities. The
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Poles noticed that there were some
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patterns in the messages which were
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only possible via certain plugboard
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settings, and so:
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> When we have collected several such cards corresponding to different
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> initial signals ..., we place them in a pile so that the squares
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> corresponding to the same daily settings are aligned and shine a
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> light beneath the pile. Only those squares which let the light
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> through will correspond to possible daily settings.
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So the brute force hardware allowed
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precalculation of "optical" computing
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devices which then narrowed down the
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possibilities enough for brute force
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to again be used for daily decodes,
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until:
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> On 10 May, the Germans invaded France and, on the same day, in
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> accordance with the best cryptographic principles, they changed their
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> Enigma procedures in such a way that the 1560 Zygalski sheets, each
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> with their carefully drilled 1000 or so holes, became just so much
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> waste cardboard.
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-Dave
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::::::
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> > "the first synthetic-aperture-radar processor was optical"
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This is also easy to believe, given Dr.
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Elachi's description of the 1981 Shuttle
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Imaging Radar:
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> The received signal is recorded on an optical film which is retrieved
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> after landing. The film ... is then processed in an optical correlator
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> to generate the final image.
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which makes sense, as one wishes to shift
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each component of the return in proportion
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to its frequency, for which one presumably
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needs a glorified prism.
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> Alternatively, the ... signal can be digitized and then recorded on
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> board or transmitted to the ground via a digital data link. This was
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> the case with the ... sensor flown in 1984.
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::::::
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* Koerner, _The Pleasures of Counting_,
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in which various aspects of the Enigma
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decoding cover four chapters, of which
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I quote from two sections of one:
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14.2: Beautiful Polish females, and
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14.3: Passing the torch
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> Churchill's romantic soul loved the excitement and secrecy surrounding
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> Bletchley. He relished the way that
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> > [t]he old procedures, like the setting up of agents, the suborning
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> > of informants, the sending of messages written in invisible ink,
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> > the masquerading, the dressing-up, the secret transmitters, and the
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> > examining of the contents of waste-paper baskets, all turned out
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> > to be largely cover for this other source, as one might keep some
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> > old-established business in rare books going in order to be able,
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> > under cover of it, to do a thriving trade in pornography and erotica
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> ...
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> Looking at the disparate, unkempt and definitely unmilitary crew
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> formed by his top code-breakers, he is said to have added to his head
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> of Intelligence "I know I told you to leave no stone unturned to find
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> the necessary staff, but I did not mean you to take me so literally!"
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--- end forwarded text
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--
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-----------------
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R. A. Hettinga <mailto: rah@ibuc.com>
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The Internet Bearer Underwriting Corporation <http://www.ibuc.com/>
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44 Farquhar Street, Boston, MA 02131 USA
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"... however it may deserve respect for its usefulness and antiquity,
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[predicting the end of the world] has not been found agreeable to
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experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
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