Zoom International Math League: Wizard Secrets (Weekly Brain Potion Discussion)

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Wizard Secrets (Weekly Brain Potion Discussion)

Adelais and Robbe are two wizards who need to communicate in secrecy through the owl post. Unfortunately, their owls keep getting intercepted by the evil wizard Evelyne who reads all their messages.

Adelais starts devising a plan. She builds a small storage box to send handwritten messages. Being wizards, Adelais and Robbe both know how to magically seal the box so that it can only be opened with a secret phrase. It is possible to seal the box with more than one phrase at once.

Adelais needs help! She needs to figure out a way to get her phrase to Robbe. There is no way for her and Robbe to meet up, and evil Evelyne is still reading all their messages (so Evelyne will read the secret phrase if Adelais sends it unsecured). How can Adelais and Robbe arrange to communicate securely with each other using only these resources?

Please share any thoughts or questions you have below. We'll monitor the responses and give our thoughts as well!

Can't they use public-key encryption?

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Does Evelyne know that the message needs to go to Robbe or does she just look in the post for any information from anyone?

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My thoughts in order of reliability(least to most):

1. Adelais could tell him to go to a random town. Then they could meet at the post office, because that is considered a standard meeting point due to there being one in every town.

2. They send a decoy box, and while Evelyn is trying to open it they send a real message.

3. Adelais could send a message hinting to it being an acronym, the password to the box.

4. The password could just be something they both know, like the name of their cat or something familiar.

5. They send a letter to a trustable middle man, who then forwards it to the next.

6. Adelais sends a message saying it is the xth word in their yth previous letter.(e.g. second word in the 53rd letter.)

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1st, Adelais sends Code A (used to open Lock A) in the storage box with Lock A on it.

2nd, Robbe receives the box and seals it with Lock B.

3rd, Adelais receives the box and unlocks Lock A, leaving Lock B.

4th, Robbe receives the box and unlocks Lock B, receiving Code A inside.

5th, Adelais and Robbe can now send secure messages to each other with Lock A and Code A!

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What is Evelyne seals it with Lock C?

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Well thought out! I didn't even think of that!

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Hold on. How does Robbe know to seal it with Lock B?

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Adelais could send a note saying “Robbe, seal this box with a lock B and send it back,” assuming Evelyne doesn’t seal it with a Lock C and she isn’t able to physically take and hide the box from the post.

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They should email instead because evil Evelyne probably isn't a hacker.

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They could modify it to look like a spam message if they were using email because if Evelyne was intercepting the messages it would end up in her spam filter.

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