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  • BRADY HARAN: Hey there, everyone.

  • Today's video is about Richard Feynman--

  • a lot of people's favorite scientist--

  • and safe breaking.

  • But I just wanted to point out at the start that most safes,

  • or secure filing cabinets, actually have one dial.

  • And if you've got a three number combination, for

  • example, you'll turn that dial in one direction, then the

  • other direction, and then back in the other direction.

  • And that's how you open it.

  • But the mock up that we've used in this video--

  • and it is a mock up, I can assure you.

  • It's about as far from a safe as you could get.

  • We've used three dials.

  • That kind of makes things a bit more visual, a bit easier

  • to understand looking at it in that way.

  • But in most cases, the sort of safes we're talking about will

  • actually be using one dial.

  • I don't want to get all the safe enthusiasts out there too

  • fired up and angry in the comments section.

  • But for now, here's Professor Bowley with his pretend safe

  • and the story of Richard Feynman and his World War II

  • safe cracking.

  • PROFESSOR ROGER BOWLEY: I'm talking about Feynman and how

  • he managed to crack safes when he was working on the atomic

  • bomb project in Los Alamos in the early '40s.

  • His wife had died.

  • So early in the 1940s, his wife died.

  • And he was stuck in the middle of Los Alamos,

  • not able to get out.

  • It was a sort of desert area around there.

  • He was stuck with lots of other theoretical physicists.

  • So he needed something for amusement.

  • And as a hobby, he tried cracking open all the safes in

  • Los Alamos.

  • Now, they had new, purpose built safes with locks on them

  • made by the Mosler lock company.

  • You can imagine 100 numbers for this, 100 numbers for

  • that, 100 numbers for that--

  • a million, a million possible settings.

  • And if you fiddle them around, it'll take about five

  • seconds to do it.

  • So if you tried to crack it, it will take

  • you about 60 days.

  • On the average, it'd be 30 days, but 60 days if you screw

  • up and it takes the last one to open it.

  • Well, Feynman was a group leader.

  • So he was given one of these in his office to keep all the

  • top secret files that he might come up with.

  • So he knew how this worked mechanically, because he

  • fiddled around with it.

  • He'd just fidget with anything.

  • He wanted to know how it worked.

  • And he found by trial and error, suppose the number

  • should be 20, it was set at.

  • Actually, it started at 25, and a lot of people didn't

  • change it from 25, naught, 25.

  • That was the default.

  • And if he wanted to crack the safe, a lot of times, people

  • left it in the default setting, because it's the

  • easiest one to remember.

  • Suppose he set it at 20.

  • Now, he found that if he tried to set it at 20 and it opened,

  • he could also set it to 21 and it would open, or 22.

  • There was some slack on this.

  • This was not mechanically perfect.

  • So there was a bit of tolerance, plus or minus 2 on

  • every single number, which meant that if you set it at

  • 20, it could be 21 or 22 or 19 or 18--

  • and the same for this dial and the same for this dial.

  • So now, if you go through all the combinations, you only

  • have to do 3, 8, 13 and so on--

  • every fifth one--

  • to make sure you cover them all.

  • Now, there are only 20 settings for this, 20 for

  • that, and 20 for that.

  • So automatically, that's gone down, oh, I can't do it.

  • Can you do it in your head, Brady?

  • It's really quite difficult.

  • 8,000 different settings--

  • now, that becomes doable mechanically.

  • It will take you something like 10 hours

  • working solidly overnight.

  • And you could do it.

  • And he could do that.

  • He worked out how to do it.

  • He found out other ways of doing this.

  • He found that most people will set a birthday, an

  • anniversary, some well-defined date that--

  • I don't know, the Independence Day in the United States of

  • America, whatever.

  • And it would not be an ordinary number, because if

  • it's going to be, say, my birthday, which is the 21st of

  • April if anybody wants to send me presents.

  • There's the 21st.

  • 04--

  • 04 is there.

  • And I'm born in 1946, which is down there.

  • So for the top one, which is the days of the month, there

  • are typically 30 days in a month.

  • So let's suppose there are just 30 and never 31.

  • 30 days in the month, you would need to set it in six

  • different positions.

  • Now, for the months, there's 12 months in the year, so you

  • may need not two, but three for that.

  • So now, we've got six settings here, three settings there.

  • And for the year--

  • well, now, the year, if it's some date, it's going to be

  • something in the past.

  • So how long back in the past is somewhat arbitrary.

  • But suppose 45 would do, and then it would be 9.

  • He was doing it 1942 or '43 or '44.

  • All right.

  • So the test would be somewhere around there.

  • So 45 is a natural number to look at, because then you

  • don't have to go back into the previous century.

  • 6 for this one, 3 for this one, and 9 for that one.

  • And you multiply them together.

  • And you get out 162.

  • So that's 162 different settings.

  • Five seconds for each, 162--

  • that's 800 seconds.

  • It's about 12 minutes.

  • So he could go in and if somebody had chosen one of

  • those dates, instead of having 8,000, he's got 162.

  • And he can do it in 12 minutes.

  • On the average, it will be six minutes, because he might be

  • reach it in the first go or he might

  • reach it after 12 minutes.

  • But he would only require 12 minutes.

  • So he would go in and make a big fuss of going into the

  • office and say, I'm not going to show the secrets.

  • These are top secret stuff.

  • I don't want everybody to know my secrets.

  • And he'd carry in a bag with tools-- screwdrivers, picks,

  • all sorts of things that people would think you crack

  • safes with--

  • shut the door, and in 12 minutes, he would do it.

  • He'd take a magazine in with him.

  • Sometimes, he'd get it done straight away and he'd do some

  • exercise and wait for 20 minutes just to make everybody

  • believe it was tough work doing this.

  • And then he'd come out with a bit of sweat on his brow,

  • saying, that was hard work.

  • So those were the main techniques that he used.

  • 162 means that this isn't safe and using your birthday or

  • anniversary is not safe.

  • But after that, he learned another trick.

  • And he got the number down to 20.

  • Out of all these million, there were 20.

  • And it turns out that if you open the safe and leave it

  • open, and there's a little draw on the bottom.

  • And he goes into somebody else's office.

  • He chats to them.

  • And the safe is open.

  • He fiddles with all the knobs.

  • And after two years of practice, he got these two

  • sorted out by fiddling around with the knobs when the safe

  • was open in somebody else's office.

  • He'd go back afterwards--

  • and they don't realize he's been doing this-- and writes

  • down these two numbers in a little book and

  • says such and such.

  • So by the end of the war, he could go

  • into anybody's office.

  • He's got the last two numbers.

  • There are 20 settings.

  • It takes him a minute and a half to open

  • the safe, or less.

  • So he really has to spin it up.

  • He has a reputation of safe cracking.

  • And everybody thinks he knows how to use picks.

  • But he's just used human nature, the tolerance of all

  • this, and deviousness, just to show how clever he was.

  • He was doing it just to show how clever he was.

  • He was obnoxious.

  • He would like to be one up on everybody else.

  • But there was a security problem there.

  • And the guy who he shared a room with was the guy who gave

  • the secrets of the bomb to the Russians,

  • which is Klaus Fuchs.

  • He was a roomie of his.

  • BRADY HARAN: But for all his showing off about safe

  • breaking, it turns out the real spy was in

  • the room with him.

  • PROFESSOR ROGER BOWLEY: Yes.

  • But I don't--

  • well, yes.

  • When you look at this, now that we live in worlds where

  • you have a little security code for everything, this

  • seems unbelievably primitive--

  • phone hacking and everything else going on.

  • But people weren't-- if you're a scientist, you're not really

  • looking at the other guy next door and wondering whether

  • he's letting all your secrets out.

BRADY HARAN: Hey there, everyone.

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ファインマンとの安全なクラッキング - Numberphile (Safe Cracking with Feynman - Numberphile)

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    潘宇將 に公開 2021 年 01 月 14 日
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