New KRACK Attack Against Wi-Fi Encryption

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Автор: Шнайер Брюс,
Об авторе: 
Американский криптограф, доктор в области компьютерных наук и популярный автор книг по ИБ. Основатель криптографической компании Counterpane Internet Security. Ранее работал на Министерство обороны США.

Mathy Vanhoef has just published a devastating attack against WPA2, the 14-year-old encryption protocol used by pretty much all wi-fi systems. Its an interesting attack, where the attacker forces the protocol to reuse a key. The authors call this attack KRACK, for Key Reinstallation Attacks

This is yet another of a series of marketed attacks; with a cool name, a website, and a logo. The Q&A on the website answers a lot of questions about the attack and its implications. And lots of good information in this ArsTechnica article.

There is an academic paper, too:

"Key Reinstallation Attacks: Forcing Nonce Reuse in WPA2," by Mathy Vanhoef and Frank Piessens.

Abstract: We introduce the key reinstallation attack. This attack abuses design or implementation flaws in cryptographic protocols to reinstall an already-in-use key. This resets the key's associated parameters such as transmit nonces and receive replay counters. Several types of cryptographic Wi-Fi handshakes are affected by the attack. All protected Wi-Fi networks use the 4-way handshake to generate a fresh session key. So far, this 14-year-old handshake has remained free from attacks, and is even proven secure. However, we show that the 4-way handshake is vulnerable to a key reinstallation attack. Here, the adversary tricks a victim into reinstalling an already-in-use key. This is achieved by manipulating and replaying handshake messages. When reinstalling the key, associated parameters such as the incremental transmit packet number (nonce) and receive packet number (replay counter) are reset to their initial value. Our key reinstallation attack also breaks the PeerKey, group key, and Fast BSS Transition (FT) handshake. The impact depends on the handshake being attacked, and the data-confidentiality protocol in use. Simplified, against AES-CCMP an adversary can replay and decrypt (but not forge) packets. This makes it possible to hijack TCP streams and inject malicious data into them. Against WPA-TKIP and GCMP the impact is catastrophic: packets can be replayed, decrypted, and forged. Because GCMP uses the same authentication key in both communication directions, it is especially affected.

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 6.0: it forces the client into using a predictable all-zero encryption key.

I'm just reading about this now, and will post more information
as I learn it.

EDITED TO ADD: More news.

EDITED TO ADD: This meets my definition of brilliant. The attack is blindingly obvious once it's pointed out, but for over a decade no one noticed it.

EDITED TO ADD: Matthew Green has a blog post on what went wrong. The vulnerability is in the interaction between two protocols. At a meta level, he blames the opaque IEEE standards process:

One of the problems with IEEE is that the standards are highly complex and get made via a closed-door process of private meetings. More importantly, even after the fact, they're hard for ordinary security researchers to access. Go ahead and google for the IETF TLS or IPSec specifications -- you'll find detailed protocol documentation at the top of your Google results. Now go try to Google for the 802.11i standards. I wish you luck.

The IEEE has been making a few small steps to ease this problem, but they're hyper-timid incrementalist bullshit. There's an IEEE program called GET that allows researchers to access certain standards (including 802.11) for free, but only after they've been public for six months -- coincidentally, about the same time it takes for vendors to bake them irrevocably into their hardware and software.

This whole process is dumb and -- in this specific case -- probably just cost industry tens of millions of dollars. It should stop.

Nicholas Weaver explains why most people shouldn't worry about this:

So unless your Wi-Fi password looks something like a cat's hairball (e.g. ":SNEIufeli7rc" -- which is not guessable with a few million tries by a computer), a local attacker had the capability to determine the password, decrypt all the traffic, and join the network before KRACK.

KRACK is, however, relevant for enterprise Wi-Fi networks: networks where you needed to accept a cryptographic certificate to join initially and have to provide both a username and password. KRACK represents a new vulnerability for these networks. Depending on some esoteric details, the attacker can decrypt encrypted traffic and, in some cases, inject traffic onto the network.

But in none of these cases can the attacker join the network completely. And the most significant of these attacks affects Linux devices and Android phones, they don't affect Macs, iPhones, or Windows systems. Even when feasible, these attacks require physical proximity: An attacker on the other side of the planet can't exploit KRACK, only an attacker in the parking lot can.

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