>From: "Wendy Nather" <wendy@nather.com>
>Subject: for Yucks
>Date: Mon, 25 Feb 2002 16:53:20 -0600
>
>
>From: Dan Geer  [mailto:geer@TheWorld.com]
>Sent: Sunday, February 24, 2002 9:16 AM
>Subject: alice and bob
>
>
>
>
>http://www.conceptlabs.co.uk/alicebob.html
>
>	The Alice and Bob After Dinner Speech
>		given at the
>	Zurich Seminar, April 1984
>		by
>	John Gordon
>	by invitation of
>	Professor James Massey
>
>Good evening Ladies and Gentlemen.
>
>There comes a time when people at a technical conference like this need
>something more relaxing. A change of pace. A shift of style. To put aside
>all that work stuff and think of something refreshingly different.
>
>So let's talk about coding theory.
>
>There are perhaps some of you here tonight who are not experts in coding
>theory, but rather have been dragged here kicking and screaming.  So I
>thought it would be a good idea if I gave you a sort of instant, five minute
>graduate course in coding theory.
>
>Coding theorists are concerned with two things.
>
>Firstly and most importantly they are concerned with the private lives of
>two people called Alice and Bob.  In theory papers, whenever a coding
>theorist wants to describe a transaction between two parties he doesn't call
>then A and B.  No.  For some longstanding traditional reason he calls then
>Alice and Bob.
>
>Now there are hundreds of papers written about Alice and Bob.  Over the
>years Alice and Bob have tried to defraud insurance companies, they have
>played poker for high stakes by mail, and they have exchanged secret
>messages over tapped telephones.
>
>If we put together all the little details from here and there, snippets from
>lots of papers, we get a fascinating picture of their lives. This may be the
>first time a definitive biography of Alice and Bob has been given.  In
>papers written by American authors Bob is frequently selling stock to
>speculators. From the number of stock market deals Bob is involved in we
>infer that he is probably a stockbroker.
>
>However from his concern about eavesdropping he is probably active in some
>subversive enterprise as well.  And from the number of times Alice tries to
>buy stock from him we infer  she is probably a speculator.
>
>Alice is also concerned that her financial dealings with Bob are not brought
>to the attention of her husband.
>
>So Bob is a subversive stockbroker and Alice is a two-timing speculator.
>
>But Alice has a number of serious problems.
>
>She and Bob only get to talk by telephone or by electronic mail.  In the
>country where they live the telephone service is very expensive. And Alice
>and Bob are cheapskates. So the first thing Alice must do is MINIMIZE THE
>COST OF THE PHONE CALL.
>
>The telephone is also very noisy.  Often the interference is so bad that
>Alice and Bob can hardly hear each other.
>
>On top of that Alice and Bob have very powerful enemies.  One of their
>enemies is the Tax Authority. Another is the Secret Police.
>
>This is a pity since their favorite topics of discussion are tax frauds and
>overthrowing the government.
>
>These enemies have almost unlimited resources.  They always listen in to
>telephone conversations between Alice and Bob.
>
>And these enemies are very sneaky.  One of their favorite tricks is to
>telephone Alice and pretend to be Bob.  Well, you think, so all Alice has to
>do is listen very carefully to be sure she recognizes Bob's voice.
>
>But no. You see Alice has never met Bob.  She has no idea what his voice
>sounds like.
>
>So you see Alice has a whole bunch of problems to face.  Oh yes, and there
>is one more thing I forgot so say  - Alice doesn't trust Bob.  We don't know
>why she doesn't trust him, but at some time in the past there has been an
>incident.
>
>Now most people in Alice's position would give up.
>
>Not Alice. She has courage which can only be described as awesome.
>
>Against all odds, over a noisy telephone line, tapped by the tax authorities
>and the secret police, Alice will happily attempt, with someone she doesn't
>trust, whom she cannot hear clearly, and who is probably someone else, to
>fiddle her tax returns and to organize a coup d'etat, while at the same time
>minimizing the cost of the phone call.
>
>A coding theorist is someone who doesn't think Alice is crazy.
>
>	Information
>
>The other thing coding theorists are concerned with is information.
>
>Nothing else is like information.  Information is very peculiar stuff. It
>can both be created and destroyed.  You can steal it without removing it.
>You can often get some just by guessing.
>
>Yet it can have great value. It can be bought and sold.
>
>One type of information is called Money.
>
>There are people who refuse to concede that money can be created and
>destroyed.  They spend their entire lives altering records and making
>adjustments to ensure that every time a bit of money leaves some place, an
>equal bit seems to appear somewhere else.
>
>These people are called accountants.
>
>	Source, channel and secrecy coding
>
>Coding theory, like Gaul, is divided into three parts called Source coding,
>channel coding and secrecy coding.
>
>	Source coding
>
>First I'll tell you about source coding.
>
>Source coding is what Alice uses to save money on her telephone bills.
>
>It is usually used for data compression.  In other words to make messages
>shorter. There is a story about a student of information theory on his first
>day at college. He had entered a strange, bizarre world.  The only sounds
>were the occasional calling out of a number by one of the professors,
>followed by laughter. One professor would say '52', there would be a short
>pause then peels of laughter. Someone else says '713'.  Same thing, everyone
>falls down laughing.  "What's  going on here" he asked his tutor.
>
>"We're telling jokes" said his tutor.
>
>"Telling Jokes?"
>
>"Yes, you see we've all worked here so long we know each other's jokes.
>There are a thousand of them.  So, being information theorists we applied
>data compression.  We just assigned them all numbers, 0 thru 999.  It saves
>a lot of time and effort.  Would you like to try?  Just say any number 0 to
>999..."
>
>He wasn't fully convinced.  But he tried.  Very quietly he whispered "477".
>
>Hardly a murmur.
>
>He looked at his tutor.  "What's wrong" he said.
>
>"Try again" says the tutor.
>
>So he does.  "318"  - same again, not a thing, hardly a murmur.
>
>"Something's wrong" he says.
>
>"Well" says the tutor, it's like this. - It's not so much the joke as the
>way you tell it!"
>
>There is a curious sequel to this story. This student eventually succeeded
>by accident in the most dramatic and unexpected way. He called out a number
>outside the range 0 to 999. "Minus 105" he said.
>
>At first there was stunned amazement, then first one professor laughed, then
>another then another, till they were all rolling about holding their sides.
>
>None of them had heard that one before.
>
>	Channel coding
>
>Next we come to channel coding.
>
>Channel coding is what Alice uses to overcome the noise and interference on
>the line. Most people have a natural instinct for channel coding.  What they
>do is to spell out important words.   This adds redundancy and enables the
>listener to cross check.  If part of the message is lost the missing bit can
>be reconstructed from the remaining part. Many organizations such as the
>military, the aviation community, the Police and so on use a standard
>phonetic alphabet specially designed for this purpose.
>
>It goes Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, etc. So one says "Mike"
>and "November", which is much clearer than saying "M" and "N" which are
>easily confused otherwise.
>
>Alice uses this to explain to Bob that her husband Michael is getting
>suspicious of her stock option dealing.
>
>"I have to tell you about Mike" she says.
>
>But Bob hears "I XXve to tell u  XXt  Xxike".
>
>"What's that again" says Bob.
>
>"I have to tell you about Mike" says Alice.
>
>"Didn't get the last word Alice" says Bob, "Can you spell it out"
>
>"Mike India Kilo Echo" says Alice.
>
>"Got India Kilo Echo, What was the first word" says Bob.
>
>"Mike"
>
>"Can you spell that?"
>
>"Mike India Kilo Echo" etc.
>
>Actually there have been lots of other phonetic alphabets, The predecessor
>to the International Phonetic Alphabet went Able, Baker, Charlie...
>
>Then there are those based on names of countries:- Africa, Brazil, Chile,
>Denmark, England, France, Greenland, Holland, India, Japan, Khazakistan,
>Lithuania, Morocco, Niger, Oman, Papua, Qatar, Russia, Spain, Tanzania,
>Uruguay, Venezuela,WestPhalia, Yemen, Xanadu, Zambia.
>
>My personal favorite is this
>
>A for 'Orses
>
>B for Mutton
>
>C for Yourself
>
>D for Mation
>
>E for Brick
>
>F for Vescence
>
>G for Police
>
>H for Consent
>
>I for Lutin
>
>J for Orange
>
>K for Teria
>
>L for Leather
>
>M for Sis
>
>N for Mation
>
>O for A Muse of Fire
>
>P for Ate
>
>Q for A Song
>
>S for Something Else
>
>T for Two
>
>U for Mism
>
>V for La France
>
>W for Mism
>
>X for Breakfast
>
>Y for Lover
>
>Z (zee) for yourself
>
>	Secrecy coding
>
>Finally we come to Secrecy Coding, or Cryptography.
>
>Secrecy Coding is what Alice uses to try to stop the tax authorities and the
>secret police understanding her telephone conversations.
>
>Now cryptographers are very peculiar people.  They have very devious minds.
>
>Sometimes they encrypt jokes.  Security agencies call these "Covert Jokes".
>People who make them are CryptoLaffers.
>
>An intelligible joke in its raw form is called the Plainjoke, and after
>encryption is called the Cipherjoke or Cryptojoke.
>
>Cipherjokes are intelligible of course only after Decryption, or as some
>people call it, after explanation.
>
>There are three kinds of attack on an unintelligible cryptojoke according to
>the Jokeanalyst's resources.
>
>Firstly there is the Cipherjoke-only attack in which the Jokeanalyst is
>assumed to have unlimited amounts of material which is alleged to be funny.
>
>Secondly and more powerfully there is the Known Plainjoke Attack in which he
>is given examples of jokes together with their explanations.
>
>But most powerful of all is the Chosen Plainjoke Attack where he gets to ask
>the Cryptolaffer to explain WHY the joke is funny.
>
>Feeble jokes are usually encrypted using only a very simple cipher, like
>changing the punch line.  This is called the DEFLECTED ENDING SYSTEM or DES.
>
>Very good jokes, the comprehension of which by outsiders could constitute a
>threat to national security, are encrypted much more securely, usually by
>completely changing the scenario, the plot and the conclusion.  This is the
>PARTICULARLY KLEVER COVERUP or PKC.
>
>The best known PKC RESISTS SERIOUS ATTACK and is therefore called the RSA.
>
>As a corollary of course, it follows that only very gifted, intelligent
>people can truly appreciate a funny speech.
>
>	Standardisation
>
>Since it is difficult to design a good cipher, and since the apparatus is
>very expensive, a lot of work has been done recently to try to standardize
>on them. Even as I speak the International Standards Organization is meeting
>to decide on this very issue. Since there is a lot of confusion on this
>point I have been asked to make the position clear. The purpose of language
>is to convey information.  This only works if both sender and receiver of
>information both use the same system.  In other words language only works
>precisely because it is standardized.
>
>The purpose of cryptography on the other hand is to make the message
>unintelligible except to one person.  In other words cryptography only works
>precisely because it is NOT standardized.
>
>So what they do is to make most of the cipher standardized, and to
>concentrate the non-standardization into one part called the key.
>
>So far so good. But of course the key, the non-standardized part, must be
>nonstandard in only standardized ways. And also key management must conform
>to certain standards. In other words standards are being formulated whereby
>the nonstandard parts, which must conform to certain standards of
>non-standardization are also to be handled only in a standardized
>nonstandard way in order to standardize on the overall non-standardization.
>
>I hope this makes the position clear.
>
>	Weak keys
>
>Many ciphers have certain bad keys.  If you use one of them the cipher is
>easily broken. For instance all-zeros is a weak key for the DES. There has
>been a lot of research done into searching for weak keys. Over the years
>more and more weak keys have been found till now one has to be quite careful
>to avoid them.
>
>Perhaps it would be a better idea if we looked for strong keys. In fact why
>not look for THE STRONGEST POSSIBLE KEY. Then we could all standardize on it.
>
>	Processing delay
>
>Coding theory is not without its problems.   The introduction of source
>coding, channel coding and secrecy coding often introduces something called
>PROCESSING DELAY.  This is the delay caused by the time it takes to do all
>this coding and decoding. These delays can be enormous.  History gives us
>instances when this delay has changed the course of world events. There is a
>recorded case of a two-word military signal which suffered a processing
>delay of 150 years. The message, deciphered at the Pentagon in 1972 simply
>read
>
>"Send Reinforcements"
>
>It was sent in 1830 from Little Bighorn by General Custer.
>
>Consider the message:
>
>"Return home at once, trip cancelled."
>
>and think of the effect on world events if it had been decoded in time. It
>was sent in 1492 by Isobella of Spain to Christopher Columbus.
>
>But these delays are nothing in comparison with the next example. We are
>told by Suetonius that Julius Caesar communicated with the Orator Cicero in
>a cipher in which 'A' was sent as 'B', 'B' as 'C' and so on. If you apply
>this cipher to HAL - the computer in the Stanley Kubrick movie: 2001 - you
>get IBM. Some correspondence from Julius Caesar to Cicero in this complex
>cipher have finally been deciphered by GCHQ and will be published in the
>June edition of Cryptologia. Their contents paint a disturbingly different
>picture of the world from Caesar's official dispatches to Rome in De Bello
>Gallico.
>
>I am privileged to have an advance copy from which I will read you an
>extract.
>
>"Alexandria, April 14th 48 BC  (think about it)
>
>Dear Marcus Tullius
>
>Thank the Gods you and I have a secure cipher.  I would not care to have our
>messages read by my enemies.  Frankly I don't trust most of the Senate.
>
>Take Mark Anthony.  Would you trust him?  He is so incompetent he couldn't
>organize a libation at an orgy.
>
>Take Gaius Brutus. Would you buy a used chariot from this man? I think he is
>plotting behind my back.  Sometimes he scares the Toga off me.
>
>And as for the Gauls.  What a bunch of morons. I thought all their problems
>would be solved when we formed the GEC - the Gallic Economic Community. But
>what happens? We guarantee minimum prices on food exports, the so called
>"Green Denarius". We provide subsidies on cheap labor saving gadgets.- Like
>slaves.
>
>Then what happens? We get a run on the Denarius.  Inflation runs at record
>levels. And they squander our subsidies on gross overproduction of wine. We
>have to sell it off cheap to the Barbarians to maintain the price level
>within the GEC.
>
>I am fed up with the whole business.  When I get back to Rome I will retire.
>I have it all planned. I lied about the size of Gaul in my official
>dispatches. I have found the most divine little spot for my retirement which
>I am keeping quiet about.
>
>I am not having those Senators getting their grubby hands on it.  And I've
>takes steps to make sure they never can. So for your ears alone Marcus
>Tullius, I have my special, secret retirement place all organized. It
>doesn't appear on any map because I authorize the maps.
>
>Officially it doesn't exist.
>
>So it can't be found or taxed.
>
>I have managed to conceal a whole extra part of Gaul!
>
>So forget De Bello Gallico.  The reality is Gaul is divided into FOUR
>parts."
>
>	The modern world
>
>Well that ends the instant course on coding theory.
>
>I would like to finish with a few words on the impact that information
>technology is having on our everyday lives. Science has marched ahead so
>fast that we take for granted the most incredible technological
>developments. Magnetrons, which were a closely guarded secret during the
>1939-45 war are now part of every microwave cooker.  And made in Japan. When
>I was a child, space travel was science fiction. Yet today, advance is so
>rapid that even the astronauts who set foot on the moon in 1969 had never
>seen a digital watch. Nor a pocket calculator.
>
>Pocket calculators!  Now there's something.  They are so complicated!
>
>I have a calculator which has sines, cosines, tangents, logarithms,
>hyperbolic functions and multiple nested parentheses. You can program it in
>Fortran, Algol, Basic, Pascal, Forth, Fifth and Sixth, ADA and Caruthers. It
>will factorize Primes for you. At present it is working on the Halting
>Problem. It translates from one language to another.
>
>>From German to Spanish.
>
>>From Macedonian to Esperanto.
>
>>From Cantonese to Greek.
>
>Or from American to English.
>
>It is in fact a multiprocessor system. There are 22 Transputers in there.
>Sometimes they organize a game of football between them.  It has a full
>color, wraparound wide screen, liquid crystal, three-dimensional holographic
>display. It's called  HoloChromaCinePhotoRamaScope. Its audio facilities
>include Dolby Digital Decaphonic surround sound. On the way here I watched
>"The Labyrinth" on it.
>
>It also has synthetic speech and a voice recognition system. I often talk to
>it. I tell it my problems. Sometimes it psychoanalyses me. It has me figured
>as paranoid.  But that's just because it keeps getting at me. But don't get
>me wrong - it can be very user friendly. In fact you can program precisely
>HOW user friendly you want it is to be on a scale from ONE to TEN.
>
>On a setting of ONE it won't even interrupt a football game to answer you.
>But on a setting of TEN it is so friendly that on a cold day it pre-heats
>its pushbuttons.
>
>But no matter who smart it SEEMS, deep down inside it is just a dumb old
>computer.
>
>One time I got really mad at it.
>
>Like all computers, it knew precisely what I wanted it to do.
>
>It know exactly what I MEANT. So why does it have to go and DO what I SAID?
>
>How do you get even with a dumb machine like that?
>
>First I tried slapping it around a little.  I pushed its buttons a bit hard.
>
>I threatened it. "How would you like a busted display" I said.
>
>But it did no good. It just said "I am virtually unbreakable - and I'm not
>going to take any notice till you enter the data nicely, like you used to
>do."
>
>Whatever I did, it always seemed to win. I decided to have a man-to-man talk
>with it.  So I sat it down and said to it "Who's the boss here, you or me?"
>
>No reply.
>
>Again I ask "Who's the boss, you or me?  Go on answer me!"
>
>"I'm thinking, I'm thinking" it said.
>
>So I hit it.
>
>Hard.
>
>Too hard.  I cracked its case.
>
>At first I thought that was the limit of the damage. But then little things
>started to go wrong.
>
>At first there was nothing definite.  Nothing you could put your finger on.
>
>Just little things like stuttering.
>
>It just didn't sound quite the same.  Its voice seemed to lack its former
>confidence.
>
>Then once I caught it making an arithmetic mistake.  Of course I didn't
>mention it.  But you could tell it knew.  Its self image was shot to pieces.
>
>Saddest of all, it forgot our anniversary - of the day I bought it. In the
>past this had been a special time for us.
>
>I just couldn't bear it any longer. One evening I tucked it up snugly in its
>case, lit candles, played a record which was popular when we first met, and
>sat down beside it.
>
>"Where did we go wrong?" I said. But it had it pride.  It wasn't about to
>weaken in front of a non-machine.
>
>"Wrong? Nothing is Wrong" it said. "Just insufficient data."
>
>But underneath you could tell it was hurt.
>
>>From there it was a rapid downhill slide.
>
>Now it just mutters to itself. It can only do very simple calculations on
>small numbers.
>
>Finally came the ultimate indignity. It lost control. It leaked electrolyte
>all over its case. I felt so bad about it.
>
>My other gadgets weren't happy about it either.  They all came out in
>sympathy for the calculator. My watch gave me a bad time. My power tools
>keep blowing fuses.
>
>Then one night last week I was driving my car back from London when suddenly
>the engine stopped all by itself on this lonely country road.
>
>I tried to get out but the solenoids were inhibited by the central locking
>computer.
>
>Suddenly the air conditioner came on and started to blow out freezing cold
>air.  It made a noise like wind whistling through the trees.
>
>Then this creepy music came from the loudspeaker.  The sort of music they
>play in movies when the hero is lost in a dark forest.
>
>I got scared.  The cold, the wind and the weird music got to me.
>
>Then it started to speak.
>
>"You're the guy who beats up pocket calculators!"