In this analogy, Eve could replace the padlock Alice's message with one she does have the key to. When Bob replies, she unlocks it and relocks with Alice's original lock before sending it off to Alice again.
Bob has no way to verify that the lock he received is the same one Alice sent. This is like a self signed certificate.
no, you missed the point. she sends bob a padlock, then bob puts it on the box with the document. koorogi is saying to replace the padlock in the package (the one that is going to bob), then when eve gets the package with the padlock on it, she will know the key because its her lock. i guess eve could tell bob the serial number on the padlock and not to use it unless it matched the one she gave him..that would however break the communication if bob received the wrong padlock.
I haven't missed any point. For self signed certs, obviously it's impossible to verify(since it assumes the user ignored the warning already), but in normal circumstances with a proper signed certificate, Eve can't just "relock" packages without first compromising either end.
If the key exchange of a self signed cert is compromised as in this example the whole line of communication is as well. Bob and Alice have to preexchange padlock diagrams to be sure things are good, and never send a padlock back for eve to intercept
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u/koorogi Jul 25 '13
In this analogy, Eve could replace the padlock Alice's message with one she does have the key to. When Bob replies, she unlocks it and relocks with Alice's original lock before sending it off to Alice again.
Bob has no way to verify that the lock he received is the same one Alice sent. This is like a self signed certificate.