KRACKs (Key Reinstallation AttaCKs) is a number of vulnerabilities in WPA2, related to key handshakes between a client and an access point.
An attacker can trick a victim into reinstalling an already-in-use key. This key (the 3rd message in a 4-way handshake) is resent multiple times by the attacker and each time installed by the client, resetting the nonce. By forcing nonce reuse in this manner, the same encryption key is used with nonce values … Read more.