Entries Tagged "cryptanalysis"

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Defeating the iPhone Restricted Mode

Recently, Apple introduced restricted mode to protect iPhones from attacks by companies like Cellebrite and Greyshift, which allow attackers to recover information from a phone without the password or fingerprint. Elcomsoft just announced that it can easily bypass it.

There is an important lesson in this: security is hard. Apple Computer has one of the best security teams on the planet. This feature was not tossed out in a day; it was designed and implemented with a lot of thought and care. If this team could make a mistake like this, imagine how bad a security feature is when implemented by a team without this kind of expertise.

This is the reason actual cryptographers and security engineers are very skeptical when a random company announces that their product is “secure.” We know that they don’t have the requisite security expertise to design and implement security properly. We know they didn’t take the time and care. We know that their engineers think they understand security, and designed to a level that they couldn’t break.

Getting security right is hard for the best teams on the world. It’s impossible for average teams.

Posted on July 18, 2018 at 6:25 AMView Comments

Critical PGP Vulnerability

EFF is reporting that a critical vulnerability has been discovered in PGP and S/MIME. No details have been published yet, but one of the researchers wrote:

We’ll publish critical vulnerabilities in PGP/GPG and S/MIME email encryption on 2018-05-15 07:00 UTC. They might reveal the plaintext of encrypted emails, including encrypted emails sent in the past. There are currently no reliable fixes for the vulnerability. If you use PGP/GPG or S/MIME for very sensitive communication, you should disable it in your email client for now.

This sounds like a protocol vulnerability, but we’ll learn more tomorrow.

News articles.

Posted on May 14, 2018 at 9:33 AMView Comments

LC4: Another Pen-and-Paper Cipher

Interesting symmetric cipher: LC4:

Abstract: ElsieFour (LC4) is a low-tech cipher that can be computed by hand; but unlike many historical ciphers, LC4 is designed to be hard to break. LC4 is intended for encrypted communication between humans only, and therefore it encrypts and decrypts plaintexts and ciphertexts consisting only of the English letters A through Z plus a few other characters. LC4 uses a nonce in addition to the secret key, and requires that different messages use unique nonces. LC4 performs authenticated encryption, and optional header data can be included in the authentication. This paper defines the LC4 encryption and decryption algorithms, analyzes LC4’s security, and describes a simple appliance for computing LC4 by hand.

Almost two decades ago I designed Solitaire, a pen-and-paper cipher that uses a deck of playing cards to store the cipher’s state. This algorithm uses specialized tiles. This gives the cipher designer more options, but it can be incriminating in a way that regular playing cards are not.

Still, I like seeing more designs like this.

Hacker News thread.

Posted on May 3, 2018 at 6:42 AMView Comments

Two NSA Algorithms Rejected by the ISO

The ISO has rejected two symmetric encryption algorithms: SIMON and SPECK. These algorithms were both designed by the NSA and made public in 2013. They are optimized for small and low-cost processors like IoT devices.

The risk of using NSA-designed ciphers, of course, is that they include NSA-designed backdoors. Personally, I doubt that they’re backdoored. And I always like seeing NSA-designed cryptography (particularly its key schedules). It’s like examining alien technology.

EDITED TO ADD (5/14): Why the algorithms were rejected.

Posted on April 25, 2018 at 6:54 AMView Comments

Security Flaw in Infineon Smart Cards and TPMs

A security flaw in Infineon smart cards and TPMs allows an attacker to recover private keys from the public keys. Basically, the key generation algorithm sometimes creates public keys that are vulnerable to Coppersmith’s attack:

While all keys generated with the library are much weaker than they should be, it’s not currently practical to factorize all of them. For example, 3072-bit and 4096-bit keys aren’t practically factorable. But oddly enough, the theoretically stronger, longer 4096-bit key is much weaker than the 3072-bit key and may fall within the reach of a practical (although costly) factorization if the researchers’ method improves.

To spare time and cost, attackers can first test a public key to see if it’s vulnerable to the attack. The test is inexpensive, requires less than 1 millisecond, and its creators believe it produces practically zero false positives and zero false negatives. The fingerprinting allows attackers to expend effort only on keys that are practically factorizable.

This is the flaw in the Estonian national ID card we learned about last month.

The paper isn’t online yet. I’ll post it when it is.

Ouch. This is a bad vulnerability, and it’s in systems — like the Estonian national ID card — that are critical.

EDITED TO ADD (11/14): More information from the researchers.

Posted on October 17, 2017 at 9:24 AMView Comments

New KRACK Attack Against Wi-Fi Encryption

Mathy Vanhoef has just published a devastating attack against WPA2, the 14-year-old encryption protocol used by pretty much all Wi-Fi systems. It’s 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.

EDITED TO ADD (11/13): The official link to the paper blocks anonymous users. Here’s an alternate.

Posted on October 16, 2017 at 8:39 AMView Comments

NSA Brute-Force Keysearch Machine

The Intercept published a story about a dedicated NSA brute-force keysearch machine being built with the help of New York University and IBM. It’s based on a document that was accidentally shared on the Internet by NYU.

The article is frustratingly short on details:

The WindsorGreen documents are mostly inscrutable to anyone without a Ph.D. in a related field, but they make clear that the computer is the successor to WindsorBlue, a next generation of specialized IBM hardware that would excel at cracking encryption, whose known customers are the U.S. government and its partners.

Experts who reviewed the IBM documents said WindsorGreen possesses substantially greater computing power than WindsorBlue, making it particularly adept at compromising encryption and passwords. In an overview of WindsorGreen, the computer is described as a “redesign” centered around an improved version of its processor, known as an “application specific integrated circuit,” or ASIC, a type of chip built to do one task, like mining bitcoin, extremely well, as opposed to being relatively good at accomplishing the wide range of tasks that, say, a typical MacBook would handle. One of the upgrades was to switch the processor to smaller transistors, allowing more circuitry to be crammed into the same area, a change quantified by measuring the reduction in nanometers (nm) between certain chip features.

Unfortunately, the Intercept decided not to publish most of the document, so all of those people with “a Ph.D. in a related field” can’t read and understand WindsorGreen’s capabilities. What sorts of key lengths can the machine brute force? Is it optimized for symmetric or asymmetric cryptanalysis? Random brute force or dictionary attacks? We have no idea.

Whatever the details, this is exactly the sort of thing the NSA should be spending their money on. Breaking the cryptography used by other nations is squarely in the NSA’s mission.

EDITED TO ADD (6/13): Some of the documents are online.

Posted on May 16, 2017 at 6:40 AMView Comments

Kalyna Block Cipher

Kalyna is a block cipher that became a Ukrainian national standard in 2015. It supports block and key sizes of 128, 256, and 512 bits. Its structure looks like AES but optimized for 64-bit CPUs, and it has a complicated key schedule. Rounds range from 10-18, depending on block and key sizes.

There is some mention of cryptanalysis on reduced-round versions in the Wikipedia entry. And here are the other submissions to the standard.

Posted on March 28, 2017 at 6:26 AMView Comments

Sidebar photo of Bruce Schneier by Joe MacInnis.