8 ms·
Thank god I could solve "Love in Kleptopia". Would have been embarrassing being a founder of a security company.
by mkagenius 10y ago
Thank god I could solve "Love in Kleptopia". Would have been embarrassing being a founder of a security company.
- cyborgx7 10y agoI'm mad at myself for not managing to figure this out myself. I guess i made more assumptions about the limitations than there were in the description of the problem.
- heartbreak 10y agoI think you'd enjoy The Code Book by Simon Singh.
- deleted 10y ago[deleted]
- JackFr 10y agoSame. It was not clear that multiple padlocks can be added to the box.
- deleted 10y ago[deleted]
- semiel 10y agoIt took me way too long for this reason. I got it instantly once I realized I had made that limitation up. I feel like there is some sort of lesson, here.
- Natsu 10y ago> I guess I made more assumptions about the limitations than there were in the description of the problem. This accounts for some high percentage of the failures in figuring out brain teasers :)
- StavrosK 10y agoI knew "the" solution was something DH-like, but my solution was: Maria mails Jan one of her padlocks, and he mails her the ring back in a box that's locked by that padlock. ...I think others are overcomplicating this.
- craigsmansion 10y ago> Maria mails Jan one of her padlocks I think the idea is that that padlock would get stolen unless it would be sent in a padlocked box.
- StavrosK 10y agoI don't know, why would someone steal a padlock unless it was attached to a box? Maybe so, though.
- mkagenius 10y agoIf not steal, can definitely make a copy of the key :)
- mcherm 10y agoThe wording of the problem is "anything sent through the mail will be stolen unless it is enclosed in a padlocked box".
- logfromblammo 10y agoJan constructs an enormous box around the entire country of Kleptopia, and places his own padlock on it from the inside. Then he mails the ring with no additional security measures. The problem is fatally flawed by not explicitly stating that boxes locked with padlocks are also not stolen, despite not being enclosed in a padlocked box.
- mikeash 10y agoJan takes a normal box and locks it. He declares the space enclosed by the box to be the "outside," and the world to be "inside."
- charlesdenault 10y agoAssuming cryptography exists in Kleptopia, couldn't he use a padlock with a combination and transmit this electronically?
- agf 10y agoTwo points -- one, that's outside of the problem statement, so no, you can't use cryptography. Two, public-key cryptography uses an exact analogy of the physical-world method, so if you have access to a cryptographic solution you've already solved the problem.
- maxerickson 10y agoInteresting to me that there is an analogy with a 1000 year old puzzle. https://en.wikipedia.org/wiki/Fox,_goose_and_bag_of_beans_puzzle https://en.wikipedia.org/wiki/Fox,_goose_and_bag_of_beans_pu...
- agf 10y agoThere isn't really an analogy here, it just seems like it. The apparent similarity between these two is due to there being multiple trips in both -- across the river in one, and through the mail in the other. But the reason for the multiple trips are entirely dissimilar, and so the similarity is purely superficial.
- Freak_NL 10y agoIt's a really good metaphor for explaining public key cryptography.
- ChoHag 10y ago> How can Jan get the ring safely into Maria’s hands? Jan will get the bus.
- delinka 10y agoOr pay for three mailings, whichever is less expensive.
- jimmaswell 10y agoAlternative solution: send her a model of the key to 3d-print
- treve 10y agoHow are you sending the model safely?
- jimmaswell 10y agoAfter she gets the package. If the post staff just break into your house to take your stuff based on internet communication, they'd find out about your ring the next time one of you mentioned it, among other problems.
- Vraxx 10y agoI presume email, and that GP misspoke when they said "model" and meant a file that the key could be modeled and printed from. That being said, that solution definitely skirts the intention of the puzzle, but would certainly work given the restrictions the puzzle did list.
- jimmaswell 10y agomodel as in 3D model
- delinka 10y agoI noticed that one proposed solution is pretty pointless: attach a key to the hasp of the first locked box. The key can then be copied ("stolen" in today's copyrights-holder's parlance) by anyone along the mailing route, and the first person to use the key gets the ring. This, aside from the fact that the key on the hasp is not "inside a padlocked box" ...
- mkagenius 10y agoYou are right. Sending key is bad idea. Another alternate solution was a bummer.. > Win at Wimbleton > 9999-9997 : Roger was wearing himself out I mean, seriously?
- joveian 10y agoShould work fine if the locked box is sent first...
- delinka 10y agoNot bad. Sadly this one has no (secure) digital parallel.
- joveian 10y ago:). OTOH, as someone interested in high latency communication protocols I wish cryptographers would hesitate to suggest a three round trip protocol at postal latency. My solution is that Jan should send the ring in a padlocked wooden box with an inner protective but unlocked box and Maria should apply a saw to the outer box. (To be fair, I can certainly imagine that in Kleptopia they know how to make excellent boxes).
- mikeash 10y agoEven simpler: send it in a padlocked cardboard box which Maria can rip open with her hands. Nothing in the problem statement says that the box itself has to be resistant to attack.
- cobalt 10y agoSimplest, drive her the key
- splintercell 10y agoOr send a bunch of hobbits with the key.
- ythl 10y agoThat puzzle needed more clarification. The solution talks about having two padlocks affixed to the same box, but I can't imagine any kind of box that can have 2 padlocks affixed to it unless the box is specifically designed to allow 2 locks.
- pkroll 10y agoA quick search for padlocked box will show many, many such boxes. It seems more common for there to be space for two or more locks, than for just one.
- ythl 10y agoMy point is that the puzzle should be updated to inform the reader that designing the right kind of box is a part of the puzzle: "Jan and Maria each have plenty of padlocks, but none to which the other has a key. Using only the padlocks, keys, and a custom-designed box, how can Jan get the ring safely into Maria’s hands?"
- mikeash 10y agoYou could always take a one-lock box and build an adapter that accepts two locks, and keeps the box locked if either lock is present.
- jonahx 10y agoThis just isn't true. I mean, yes they exist, but the norm is overwhelmingly a single latch with room for a single lock.
- pkroll 10y agoWithout a third party showing sales of padlock boxes with and without space for two or more locks, there's no actual way of being SURE which is more common. Even if there are ten times as many boxes available that only have space for a single lock, what matters in the case of the puzzle is, a box with space for two or more locks is readily available. Suggesting in the puzzle "by the way the box has space for two locks" really kind of destroys the "puzzle" aspect.
- LeifCarrotson 10y agoI solved it a little differently than the suggested method. The suggested solution requires a box that is capable of being locked in both the lid and box by two padlocks. It also requires (Spoiler!) the ring to make two pointless transits, which could be expensive if it was large. What if, instead, the box was capable of admitting only one padlock? Then Jan would padlock it closed. On receiving the locked box, Maria locks her padlock to Jan's, and returns the box (still locked with Jan's padlock, and not necessarily containing anything.) Then, on receiving the box back from Maria, Jan can form a chain that can be broken by either his padlocks (which he can remove) or by Maria's padlock (which she can remove). Then he can attach the chain to any box. Perhaps he should clip one more of his padlocks only to hers, so she can also select a new box. Of course, this relies on some properties of padlocks that are not necessarily transferrable to cryptography.
- mkagenius 10y ago> Jan can form a chain that can be broken by either his padlocks or by Maria's padlock The box cannot be opened by Maria, breaking the rear end of chain wouldn't help at all.
- LeifCarrotson 10y agoThe chain would start: Box - J - Lid Maria adds hers: Box - J - Lid | M Jan can open his padlock, releasing hers, and transform this to: Box - J - M - J - Lid Which Maria can open. An optimization could be: Box - M - J - Lid This is available if Maria could fit her padlock through the port in the box simultaneously with Jan's there, and send that back so Jan could remove his initial box padlock. And the arrangement Box - M - J - Lid | | J M Would let either start a new box, using the J - M - J or M - J - M chaining as needed.
- mkagenius 10y agoNicely done. Understood the chaining solution now. One small assumption in that would be that the chain remains taut enough to not leave any gaps to slide the hands into the box (since the lid's hook is no longer in touch with the box).
- iliis 10y agoMy sister's solution: Send the ring in a box with a combination lock ;) Edit: Ah, charlesdenaul already proposed that. You wouldn't need cryptography, as the problem doesn't state that the postal service also monitors the Internet.