Presented at
Black Hat Europe 2017,
Dec. 7, 2017, 2 p.m.
(60 minutes)
<div>We introduce key reinstallation attacks. These attacks abuse features of a protocol to reinstall an already in-use key, thereby resetting</div><div>nonces and/or replay counters associated to this key. We show that our novel attack technique breaks several handshakes that are used in a WPA2-protected network.</div><div><br></div><div>All protected Wi-Fi networks use the 4-way handshake to generate fresh session keys. The design of this handshake was proven secure, and over its 14-year lifetime no weaknesses have been found in it. However, contrary to this history, we show that the 4-way handshake is vulnerable to key reinstallation attacks. In such an attack, the adversary tricks a victim into reinstalling an already in-use key. This is achieved by manipulating and replaying handshake messages. When the victim reinstalls the key, the associated incremental nonce and replay counter is reset to its initial value. Apart from breaking the 4-way handshake, we also show that our key reinstallation attack breaks the group key and Fast BSS Transition (FT) handshake. The impact of our attacks depend on both the handshake being targeted, and the data-confidentiality protocol in use. Simplified, against AES-CCMP, an adversary can replay and decrypt packets, but cannot forge packets. Still, this makes it possible to hijack TCP streams and inject malicious data into them. Against WPA-TKIP and GCMP, the impact is catastrophic: an adversary can replay, decrypt, and forge arbitrary packets. Rather surprisingly, GCMP is especially affected because it uses the same authentication key in both communication directions.</div><div><br></div><div>Finally, we confirmed our findings in practice, and found that every Wi-Fi device is vulnerable to some variant of our attacks. Notably, our attack is exceptionally devastating against Android and Linux: it forces the client into using a predictable all-zero encryption key.</div><div><br data-mce-bogus="1"></div>
Presenters:
-
Mathy Vanhoef
- Postdoctoral Researcher, imec-DistriNet, KU Leuven
Mathy Vanhoef is a postdoctoral researcher at KU Leuven, where he currently performs research on automatically discovering logical vulnerabilities in network protocol implementations. Previously he performed research on streamciphers, and discovered a new attack on RC4 that made it possible to exploit RC4 as used in TLS in practice (the RC4 NOMORE attack). He also focuses on wireless security, where he turns commodity wifi cards into state-of-the art jammers, defeats MAC address randomization, and breaks protocols like WPA-TKIP. He also did research on information flow security to assure cookies don't fall in the hands of malicious individuals. Apart from research, he knows a thing or two about low-level security, reverse engineering, and binary exploitation. He regularly participates in CTFs with KU Leuven's Hacknamstyle CTF team.
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