File 844-846: Corpse Among The Fruits (NO SPOILER)

[Black Demon 466]

THIS THREAD will be used to discuss the ENGLISH ONLY VERSION. In other words, if you only read early spoilers or the Chinese scanlation and wish to discuss them, this is NOT the right place for you!

RULES OF THE ENGLISH ONLY NO SPOILER DISCUSSION THREAD:

1. DO NOT POST any kind of spoiler involving the case (Pictures, Texts, Information, Full Scans...) of any language. Even posting spoilers in spoiler boxes is not allowed.

2. Please DO NOT reveal, give hints or talk about any information or event that has not yet happened in the English releases in this thread. 

Q&A:

1. Why is this whole thing necessary ?
A: Click http://www.detectiveconanworld.com/forum/topic/3597-split-into-spoiler-and-non-spoiler-deduction-threads/'>here.

2. Can I join the discussion in the other thread as well ?
A: Of course you can. HOWEVER, as mentioned in the rules above, you MUST NOT reveal, give hints or talk about ANYTHING that spoils in this thread if you do.

 

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844 English is out !

[Chekhov MacGuffin 1089]

This reminds me of a cryptography puzzle

I think this one is the asymmetric key version with a three pass protocol. Gosho seems to have set the trick up so we can assume the locks are unpickable and there are no spare keys for the locks. (That doesn't mean there are no extra lock and key sets though!) Even so, there are a whole bunch of attack routes available assuming the box is not authenticated. For the sake of explaining, the sender Kasuga who puts the fruit in will be called K. Takeki, the critic with the other lock is the receiver and will be called T. The man in the middle attacker will be M.

1) The attacker could swap out the box if both sender and receiver can't instantly recognize they were sent a different box or locks than normal. If M has two spare locks, fruitlike objects, and a spare box, he could intercept the box coming from K and put his own lock on it and send it back to K, making K think T received it. K takes off his own lock thinking the lock on there currently is Ts and sends to box back where M intercepts it, opens his own lock and peeks inside the box. Meanwhile M sends his own box with his lock and fruits to T, so T thinks it is from K. The three pass is carried out with M in the middle and T winds up with M's box, thinking it is from K. If this is what happened when T opened the box to publicly reveal the contents, K would find out he had been tricked, but T wouldn't know unless K told him. The trick would not be discovered if M could fully complete the exchange with K first, so M could put the same fruits in his box to T.

2) The contents of the box don't seem to be authenticated either -- if the sender did not include a special secret item in the box that the receiver is expecting then the receiver can't tell if an attacker tampered with the contents of the box. M, using the second version the attack described above, could completely get away with it.

3) Trick box: if the box can open any other way, anyone could fiddle with it.

4) A non-trustworthy receiver or sender could collaborate with M to fix the final contents. I'm going to guess K is likely trustworthy because he will feel the brunt of the blame if cheating occurs. T's side though seems to have holes even though T himself was probably trustworthy.

To review the security details known so far, the security of the sender Kasuga's lock and key are unknown, but the receiving Takeki thinks the lock is in good working order. I think we can assume the receiver's lock is completely open to swapping because it was plonked in an easily accessible drawer. The receiver's key is locked up in a bank vault until the show and seems to have been escorted to the premises by assumed trustworthy bankers. Anyone who could tamper with the vault or direct the bankers could switch the receiver's key. There is a brief window during the key hand-off where the person passing the key to Osamu Kenzaki could pull a sleight of hand to swap the keys. I think we can assume Osamu is trustworthy as an unlocker because he is a recurring character. The three-pass exchange itself seems to be fairly lax, suggesting that M messing with the exchanges is a viable option.

The sender Kasuga will likely take the brunt of the suspicion for the murder given the situation so far, and seeing how his reputation was already being doubted, I think he wouldn't have chosen this method as long as this crime was premeditated. Taruoka, as the one doing the handoff and directing the others (maybe even the bankers?) is in the best manipulator position. I think I'm most suspicious of him for now. Furuya had access to the receiver's lock and was not watched, so he had opportunity, just not quite as much as Taruoka who handled the key too.

[Aunkang 0]

How to read T_T