wifi wpa2 security : why can't i just use data captured from the client to the AP to authenticate to the AP -


so did lot of searching internet on topic of how 4 way handshake in wpa2 wifi works.

i`m still confused why can't use captured data moving client ap initial fresh authentication. process: 4 way handshake

scenario wanna create is:

client mitm ap sends auth data forwards receives , sends response

so ap believe mitm client.

can gimme few reasons why isn't possible. thank you

in four-way handshake, first message ap contains large random number (known nonce, , represented anonce in diagram posted). client combines number random number generate (called snonce in diagram), mac address, and, importantly, secret shares ap create whats called ptk (pairwise transient key).

it uses key "sign" random number (snonce), , send snonce+signature ap. ap uses random number (anonce), number received in message (snonce), mac address of client sent message, and, again importantly, shared secret (which is, functionally, wifi password) gererate same ptk client has generated.

if ap able use ptk has generated verify signature on message received client, knows client must have known current anonce, snonce sent ap, own mac address, , shared secret; otherwise, wouldn't able create same ptk. therefore, replaying recording of earlier handshake won't authenticate ap; providing message signed key created correct shared secret, (assumedly) right mac address, , valid snonce, different anonce 1 ap sent @ start of handshake. ap won't able tell why key wrong, fail authentication regardless.

of course, things different if ap happened send same anonce sent in recorded transaction. able authenticate recorded data, , ap none wiser. useless, however, still wouldn't have keys you'd need encrypt/decrypt data exchanging ap.


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