Challenge Questions Blog

### Challenge Questions

So do you have a Challenge Question that could stump the community? Then submit the question with the "correct" answer and we'll post it. If it's really good, we may even roll it up to Specs & Techs. You'll be famous!

Answers to Challenge Questions appear by the last Tuesday of the month.

 Previous in Blog: Series Stumper: Newsletter Challenge (July 2019) Next in Blog: Night Flights: Newsletter Challenge (September 2019)

# Pilferland Puzzle: Newsletter Challenge (August 2019)

Posted July 31, 2019 5:01 PM
Pathfinder Tags: challenge question mail pilferton

This month's IEEE GlobalSpec challenge question is:

Joe and Maura live far from each other and have fallen in love via online dating, and Joe wishes to mail her a ring. Unfortunately, they both live in Pilferland, where all packages will be stolen unless enclosed in a padlocked box. Joe and Maura each have plenty of padlocks, but none to which the other has a key. How can Joe get the ring safely into Maura’s hands?

This puzzle came from Caroline Calderbank, daughter of mathematicians Ingrid Daubechies and Rob Calderbank. In the solution she had in mind, Joe sends Maura a box with the ring in it and one of his padlocks on it. Maura then affixes her own padlock to box and mails it back with both padlocks on it. When Joe gets it he removes his padlock and sends the box back to Maura.

This idea is fundamental to Diffie-Hellman key exchange, an historic breakthrough in cryptography.

Other solutions are possible as well, depending on starting assumptions. One requires that Joe find a padlock whose key has a large hole, or at least a hole which can be sufficiently enlarged by drilling, so that the key can be hooked onto a second padlock’s hasp.

Joe uses this second padlock, with the aforementioned key hooked on its hasp, to lock a small empty box which he then sends to Maura. When enough time has passed for it to get there (perhaps he awaits an email acknowledgment from Maura) he sends the ring in another box, locked by the first padlock. When Maura gets the ring box, she picks up the whole first box and uses the key affixed to it to access her ring.

Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
5
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 32984
#1

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

07/31/2019 5:30 PM

Jon sends Maura the ring in a box with one of his locks on it...

Maura puts one of her locks on the box with Jon's...now double locked...and sends it back to Jon...

Jon removes his lock and mails the box back to Maura...

Maura receives box, removes her lock, and texts back picture of her with ring on finger...

So Happy!!!

__________________
All living things seek to control their own destiny....this is the purpose of life
Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 32984
#2

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/01/2019 10:35 AM

Of course Jon had to install a larger clasp on the box, which nobody mentioned...so he cheated....clasps generally only accommodate one lock, which is the assumption...To think that a locked box is secure requires suspension of reasoning to begin with, and the lack of locksmiths doesn't make sense either....

..and as we all know, with the right tool, a lock is no obstacle...

__________________
All living things seek to control their own destiny....this is the purpose of life
Power-User

Join Date: Apr 2007
Posts: 212
#5

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/01/2019 11:40 PM

A lockout/tagout hasp would cover it.

Power-User

Join Date: Dec 2007
Posts: 177
#11

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 7:20 AM

you know what happens when we assume something.

Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 9657
#3

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/01/2019 8:00 PM

Sounds a bit like Public Key Cryptography...

Guru

Join Date: Mar 2007
Location: by the beach in Florida
Posts: 32984
#4

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/01/2019 8:11 PM

Reminds me of the Boss 302 with 2 keys...

__________________
All living things seek to control their own destiny....this is the purpose of life
Anonymous Poster #1
#8

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 2:34 AM

Excellent solution

Guru

Join Date: Aug 2005
Posts: 5754
#26

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

12/03/2019 8:23 AM

"Maura receives box, removes her lock, and"..... by that time Schrödinger's cat is dead from starvation.

__________________
We are alone in the universe, or, we are not. Either way it's incredible... Adapted from R. Buckminster Fuller/Arthur C. Clarke
4
Guru

Join Date: Feb 2013
Posts: 716
#6

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 12:25 AM

How can Jon get the ring safely into Maura’s hands?

The OP doesn't seem to put many constraints on this question, even though it is set up so that it LOOKS like there are constraints. So this seems like a perfect problem to practice thinking out of the box, so to speak. I note that they both live in Pilferland, which does not sound like a very large place, and saying they live "far from each other" is a very vague statement.

He can walk, drive, bicycle, Uber, or take a train to Maura's house, take her to a nice restaurant, have the restaurant serve champagne, hire a violinist, or at least an accordionist, and give it to her in person, like any decent suitor should do.

Or, if for some reason the OP does not want to permit this, being an engineer after all and not very romantic, then Jon can put the ring in a box, put one of his locks on it, and mail it to Maura. Presto! The ring is IN her hands. Not ON her hand, but close enough. Or Maura can now use her lock-picking skills or her bolt-cutters to remove the lock and take the ring out and put it on. Or she can drive over the box to smash it, or use a sledgehammer to pound the box to pieces, and pick the ring out of the remains and put it on. (She could sit by the box and wait a very long time for the ring to tunnel out of the box by quantum physics. If that ever happens, it is likely to be only a short distance away and she can find it easily and put it on if she is still there. But she is not likely to still be there, so I don't recommend this one.) Presto! It is ON her hand.

Or Jon can deliver the ring to her without using the mail, by asking a friend to deliver it, or using UPS, or FedEx, or Owl Delivery, or drone.

Or Jon can go buy a combination lock, use that lock to send the ring to Maura, and then email the combination to Maura.

If none of these are permitted, then he can use Solar Eagle's solution of mailing it back and forth 3 times, which seems like the worst possible solution aside from quantum physics.

But here is what I would do.

He can contact a jeweler near Maura, have him make the ring, and have Maura pick it up so that it can be sized properly while she is there.

__________________
canary
Commentator

Join Date: Nov 2013
Location: United Kingdom
Posts: 65
#7

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 2:24 AM

simple, just saw the lock off...done :)

Guru

Join Date: Sep 2009
Location: Louisville, OH
Posts: 1797
#14

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 9:44 AM

The hasp is often hardened, so a saw wouldn't work. But an abrasive cutoff wheel should. Or the "hot wrench."

__________________
Lehman57
Power-User

Join Date: Nov 2011
Location: NASA-Glenn Research Center, Cleveland Ohio
Posts: 389
#24

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/19/2019 8:25 AM

dremel tool works on hardened locks

Participant

Join Date: Jan 2019
Posts: 3
#9

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 6:54 AM

Send the ring in a padlocked box and call Maura and tell her the key number and have her make a key to the box, or just send the box with a combination padlock box and tell her the combination.

Very easy to solve when you think out of the box.

Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1782
#10

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 7:01 AM

Jon could send Maura the key by separate route, or ask Maura to send him a padlock and key.....useful if needed again).

__________________
When arguing, remember mud-slinging = lost ground.
Power-User

Join Date: Nov 2011
Location: NASA-Glenn Research Center, Cleveland Ohio
Posts: 389
#12

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 8:07 AM

I think that Jon needs to save his money, so he can buy a place outside of Pilferland, someplace like Grafton, Ohio where we keep that vermin out.

Guru

Join Date: Jul 2006
Location: CA (Central Arkansas, USA)
Posts: 599
#13

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 9:11 AM

Use a combination lock. - No key. -- JHF

__________________
If it's too good to be true, it probably isn't
Guru

Join Date: Mar 2011
Location: Sebastopol, California
Posts: 1128
#15

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 10:56 AM

John gets in the box and mails himself with the ring, and gets pilfered by Julie who is even more beautiful than what's her name and they live happily ever after.

__________________
Most people are mostly good most of the time.
Guru

Join Date: Mar 2011
Location: ''but, don't we get PAID to ask questions?...''
Posts: 1661
#16

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/02/2019 1:11 PM

Jon should man-up and travel directly to Maura to present her the ring, personally, after both have ''sensed'' enough of the mutual chemistry, non-electronically, to justify actually ''tendering'' the offer in question...

__________________
''illigitimi non carborundum...''(i.e.: don't let the fatherless (self-deluding,sabotaging, long-term-memory-impaired, knee-jerking, cheap-shotting, mono-syllabic, self-annointed, shadow-lurking, back-biting, off-topic-inquisitors) grind you down...)
Participant

Join Date: Jun 2015
Posts: 4
#17

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/13/2019 12:33 PM

Break off the engagement. Maura has shown she's too high-maintenance. Exchange the ring for cash, put a down payment on one of those lifelike programmable robot girls. Jon will be better off. Maura is probably made up. Some 40 year Nigerian fraud guy.

Guru

Join Date: Feb 2013
Posts: 716
#18

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/13/2019 2:43 PM

Since they've only met online, he should send her a virtual ring, using online photos from jewelry stores or anywhere else. He can take his pick of images of the most beautiful and valuable rings ever made, ever imagined, or ever unmade, even the One Ring to Rule Them All. That one may be a bit on the dangerous side, and is better for birthdays, not engagements. How about Nenya, the ring Galadriel wore?

__________________
canary
Member

Join Date: Apr 2013
Posts: 7
#19

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/16/2019 9:13 AM

Joe can email a CAD/CAM file with the design of the ring and she can get it 3D printed using a filament, High speed sintering, or laser sintering process.

Participant

Join Date: Aug 2019
Posts: 1
#20

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/16/2019 9:30 AM

Hey, Joe. Just send her the ring in a lockbox.

Then scan the key and send her the file so she can print it on a 3D printer.

While you're at it, scan the ring in case the technology advances to the point you can reprint it in gold if she ever loses it.

Member

Join Date: Apr 2013
Posts: 7
#21

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/16/2019 10:12 AM

The technology exists. See my post above. Laser sintering of metals is very common. Gold should be a cinch.

Participant

Join Date: Aug 2019
Posts: 1
#22

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/16/2019 10:14 AM

If this is considered difficult.... Simply hand it to her.

__________________
Jason Heath
Guru

Join Date: May 2007
Location: Australia.
Posts: 1642
#23

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/17/2019 11:07 PM

There would appear to be number of solutions? With the answer evolving around the word KEY, and the things at his disposal. Post, internet and time?

(1) Key in the post, a very good answer given by SE.

(2) Key too a combination lock, given over the internet.

(3) Key too her account received over the internet, buy the ring herself.

(4) Key of time, buy ring herself and pay at a later date.

So what's the KEY too the puzzle?

Power-User

Join Date: Nov 2012
Posts: 431
#25

### Re: Pilferland Puzzle: Newsletter Challenge (August 2019)

08/22/2019 9:48 AM

__________________
Nobody realizes that some people expend tremendous energy merely to be normal. -Camus
Interested in this topic? By joining CR4 you can "subscribe" to