question about public key crypto

[spooderman]

i'm a noob but would appreciate an explanation here.

so my understanding with pub key crypto is that i send you my pub key, you send me yours. and the messages that we send to eachother which are encrypted are unreadable to anyone that doesn't hold the relevant private keys.

but what i don't understand is how this helps when there is a (wo)man in the middle "eve".

unless you exchange public keys in person eve could just be intercepting your messages and really you are both encrypting messages to eve's pub key and not the intended recipient and obviously she forwards it on, after having read the content and re-encrypting it using the correct public key.

i ask because i try to explain this stuff to people who know even less than me and realise i don't know what i'm talking about.

help a layman pls.

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[criptix]

you use the pub key to encrypt your message and your priv key will decrypt it.

pub key is used to verify the origin of the message and the message itself.

(you can not decrypt with pubkey because it should not be possible or rather very hard to compute priv key from pub key)

now sharing the pub key is a obvious problem and one attack vector which you mentioned is a man in the middle attack.
so the safest bet would be exchanging pub keys in person, make the person remember it and destroy all evidence of the pub key.

one solution for it lies in future quantum cryptography where it shouldn't be possible to perform a men in the middle attack without getting noticed (it is based on some laws of quantum mechanics).


*edit

[spooderman]

nice thanks. was wondering how SSL works. but now i've learned the pub keys are always compared against a copy held by an authority.

that's an interesting possibility with quantum computing!

[kenko]

sorry,, im also not understand, what is public key crypto, anyone can explain it here