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This fun puzzle illustrates some of the ideas: Bob wants to send Alice something valuable in the mail. Unfortunately the postal system is very corrupt and very
by spaghetti 14y ago
This fun puzzle illustrates some of the ideas: Bob wants to send Alice something valuable in the mail. Unfortunately the postal system is very corrupt and very efficient. Any package containing a valuable item will always be spotted by postal workers. If the package doesn't have a lock the postal workers will steal the item. Also postal workers will always spot any key sent through the mail and hold it indefinitely. So even if a locked box is sent through and Alice receives it she will never receive the key when it comes through hence she can't obtain the package contents. How can Bob successfully deliver a valuable item to Alice?
Answer: Bob puts the item in a box with a lock and sends to Alice. Alice receives the box, places her lock on it and sends it back to Bob. Bob removes his lock and sends the box back to Alice. Now Alice removes her lock and obtains the package contents.
- jethroalias97 14y agoWhat you have described is more or less Diffie-Hellman. Unfortunately this alone wont guarantee your package's safe passage. If it did Verisign, would be out of a job. The flaw is, you can basically just have the same scenario but replace Alice with the post office: Bob puts the item in a box with a lock and sends to Alice. Post office intercepts the box, places their lock on it and sends it back to Bob. Bob removes his lock and sends the box back to Alice. Now the post office removes their lock and obtains the package contents. The only way around this is to have some truly trusted third party. Even in RSA, if you aren't absolutely certain of the other user's public key, it won't work, which is why web-of-trust and other techniques are used.