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New SHA-1 Attack

There’s a new, practical, collision attack against SHA-1:

In this paper, we report the first practical implementation of this attack, and its impact on real-world security with a PGP/GnuPG impersonation attack. We managed to significantly reduce the complexity of collisions attack against SHA-1: on an Nvidia GTX 970, identical-prefix collisions can now be computed with a complexity of 261.2rather than264.7, and chosen-prefix collisions with a complexity of263.4rather than267.1. When renting cheap GPUs, this translates to a cost of 11k US$ for a collision,and 45k US$ for a chosen-prefix collision, within the means of academic researchers.Our actual attack required two months of computations using 900 Nvidia GTX 1060GPUs (we paid 75k US$ because GPU prices were higher, and we wasted some time preparing the attack).

It has practical applications:

We chose the PGP/GnuPG Web of Trust as demonstration of our chosen-prefix collision attack against SHA-1. The Web of Trust is a trust model used for PGP that relies on users signing each other’s identity certificate, instead of using a central PKI. For compatibility reasons the legacy branch of GnuPG (version 1.4) still uses SHA-1 by default for identity certification.

Using our SHA-1 chosen-prefix collision, we have created two PGP keys with different UserIDs and colliding certificates: key B is a legitimate key for Bob (to be signed by the Web of Trust), but the signature can be transferred to key A which is a forged key with Alice’s ID. The signature will still be valid because of the collision, but Bob controls key A with the name of Alice, and signed by a third party. Therefore, he can impersonate Alice and sign any document in her name.

From a news article:

The new attack is significant. While SHA1 has been slowly phased out over the past five years, it remains far from being fully deprecated. It’s still the default hash function for certifying PGP keys in the legacy 1.4 version branch of GnuPG, the open-source successor to PGP application for encrypting email and files. Those SHA1-generated signatures were accepted by the modern GnuPG branch until recently, and were only rejected after the researchers behind the new collision privately reported their results.

Git, the world’s most widely used system for managing software development among multiple people, still relies on SHA1 to ensure data integrity. And many non-Web applications that rely on HTTPS encryption still accept SHA1 certificates. SHA1 is also still allowed for in-protocol signatures in the Transport Layer Security and Secure Shell protocols.

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Signed Malware

Stuxnet famously used legitimate digital certificates to sign its malware. A research paper from last year found that the practice is much more common than previously thought.

Now, researchers have presented proof that digitally signed malware is much more common than previously believed. What’s more, it predated Stuxnet, with the first known instance occurring in 2003. The researchers said they found 189 malware samples bearing valid digital signatures that were created using compromised certificates issued by recognized certificate authorities and used to sign legitimate software. In total, 109 of those abused certificates remain valid. The researchers, who presented their findings Wednesday at the ACM Conference on Computer and Communications Security, found another 136 malware samples signed by legitimate CA-issued certificates, although the signatures were malformed.

The results are significant because digitally signed software is often able to bypass User Account Control and other Windows measures designed to prevent malicious code from being installed. Forged signatures also represent a significant breach of trust because certificates provide what’s supposed to be an unassailable assurance to end users that the software was developed by the company named in the certificate and hasn’t been modified by anyone else. The forgeries also allow malware to evade antivirus protections. Surprisingly, weaknesses in the majority of available AV programs prevented them from detecting known malware that was digitally signed even though the signatures weren’t valid.

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New Techniques in Fake Reviews

Research paper: “Automated Crowdturfing Attacks and Defenses in Online Review Systems.”

Abstract: Malicious crowdsourcing forums are gaining traction as sources of spreading misinformation online, but are limited by the costs of hiring and managing human workers. In this paper, we identify a new class of attacks that leverage deep learning language models (Recurrent Neural Networks or RNNs) to automate the generation of fake online reviews for products and services. Not only are these attacks cheap and therefore more scalable, but they can control rate of content output to eliminate the signature burstiness that makes crowdsourced campaigns easy to detect.

Using Yelp reviews as an example platform, we show how a two phased review generation and customization attack can produce reviews that are indistinguishable by state-of-the-art statistical detectors. We conduct a survey-based user study to show these reviews not only evade human detection, but also score high on “usefulness” metrics by users. Finally, we develop novel automated defenses against these attacks, by leveraging the lossy transformation introduced by the RNN training and generation cycle. We consider countermeasures against our mechanisms, show that they produce unattractive cost-benefit tradeoffs for attackers, and that they can be further curtailed by simple constraints imposed by online service providers.

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The Future of Forgeries

This article argues that AI technologies will make image, audio, and video forgeries much easier in the future.

Combined, the trajectory of cheap, high-quality media forgeries is worrying. At the current pace of progress, it may be as little as two or three years before realistic audio forgeries are good enough to fool the untrained ear, and only five or 10 years before forgeries can fool at least some types of forensic analysis. When tools for producing fake video perform at higher quality than today’s CGI and are simultaneously available to untrained amateurs, these forgeries might comprise a large part of the information ecosystem. The growth in this technology will transform the meaning of evidence and truth in domains across journalism, government communications, testimony in criminal justice, and, of course, national security.

I am not worried about fooling the “untrained ear,” and more worried about fooling forensic analysis. But there’s an arms race here. Recording technologies will get more sophisticated, too, making their outputs harder to forge. Still, I agree that the advantage will go to the forgers and not the forgery detectors.

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Forging Voice

LyreBird is a system that can accurately reproduce the voice of someone, given a large amount of sample inputs. It’s pretty good — listen to the demo here — and will only get better over time.

The applications for recorded-voice forgeries are obvious, but I think the larger security risk will be real-time forgery. Imagine the social engineering implications of an attacker on the telephone being able to impersonate someone the victim knows.

I don’t think we’re ready for this. We use people’s voices to authenticate them all the time, in all sorts of different ways.

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Organizational Doxing and Disinformation

In the past few years, the devastating effects of hackers breaking into an organization’s network, stealing confidential data, and publishing everything have been made clear. It happened to the Democratic National Committee, to Sony, to the National Security Agency, to the cyber-arms weapons manufacturer Hacking Team, to the online adultery site Ashley Madison, and to the Panamanian tax-evasion law firm Mossack Fonseca.

This style of attack is known as organizational doxing. The hackers, in some cases individuals and in others nation-states, are out to make political points by revealing proprietary, secret, and sometimes incriminating information. And the documents they leak do that, airing the organizations’ embarrassments for everyone to see.

In all of these instances, the documents were real: the email conversations, still-secret product details, strategy documents, salary information, and everything else. But what if hackers were to alter documents before releasing them? This is the next step in organizational doxing­ — and the effects can be much worse.

It’s one thing to have all of your dirty laundry aired in public for everyone to see. It’s another thing entirely for someone to throw in a few choice items that aren’t real.

Recently, Russia has started using forged documents as part of broader disinformation campaigns, particularly in relation to Sweden’s entering of a military partnership with NATO, and Russia’s invasion of Ukraine.

Forging thousands — or more — documents is difficult to pull off, but slipping a single forgery in an actual cache is much easier. The attack could be something subtle. Maybe a country that anonymously publishes another country’s diplomatic cables wants to influence yet a third country, so adds some particularly egregious conversations about that third country. Or the next hacker who steals and publishes email from climate change researchers invents a bunch of over-the-top messages to make his political point even stronger. Or it could be personal: someone dumping email from thousands of users making changes in those by a friend, relative, or lover.

Imagine trying to explain to the press, eager to publish the worst of the details in the documents, that everything is accurate except this particular email. Or that particular memo. That the salary document is correct except that one entry. Or that the secret customer list posted up on WikiLeaks is correct except that there’s one inaccurate addition. It would be impossible. Who would believe you? No one. And you couldn’t prove it.

It has long been easy to forge documents on the Internet. It’s easy to create new ones, and modify old ones. It’s easy to change things like a document’s creation date, or a photograph’s location information. With a little more work, pdf files and images can be altered. These changes will be undetectable. In many ways, it’s surprising that this kind of manipulation hasn’t been seen before. My guess is that hackers who leak documents don’t have the secondary motives to make the data dumps worse than they already are, and nation-states have just gotten into the document leaking business.

Major newspapers do their best to verify the authenticity of leaked documents they receive from sources. They only publish the ones they know are authentic. The newspapers consult experts, and pay attention to forensics. They have tense conversations with governments, trying to get them to verify secret documents they’re not actually allowed to admit even exist. This is only possible because the news outlets have ongoing relationships with the governments, and they care that they get it right. There are lots of instances where neither of these two things are true, and lots of ways to leak documents without any independent verification at all.

No one is talking about this, but everyone needs to be alert to the possibility. Sooner or later, the hackers who steal an organization’s data are going to make changes in them before they release them. If these forgeries aren’t questioned, the situations of those being hacked could be made worse, or erroneous conclusions could be drawn from the documents. When someone says that a document they have been accused of writing is forged, their arguments at least should be heard.

This essay previously appeared on TheAtlantic.com.

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Powerful Bit-Flipping Attack

New research: “Flip Feng Shui: Hammering a Needle in the Software Stack,” by Kaveh Razavi, Ben Gras, Erik Bosman Bart Preneel, Cristiano Giuffrida, and Herbert Bos.

Abstract: We introduce Flip Feng Shui (FFS), a new exploitation vector which allows an attacker to induce bit flips over arbitrary physical memory in a fully controlled way. FFS relies on hardware bugs to induce bit flips over memory and on the ability to surgically control the physical memory layout to corrupt attacker-targeted data anywhere in the software stack. We show FFS is possible today with very few constraints on the target data, by implementing an instance using the Rowhammer bug and memory deduplication (an OS feature widely deployed in production). Memory deduplication allows an attacker to reverse-map any physical page into a virtual page she owns as long as the page’s contents are known. Rowhammer, in turn, allows an attacker to flip bits in controlled (initially unknown) locations in the target page.

We show FFS is extremely powerful: a malicious VM in a practical cloud setting can gain unauthorized access to a co-hosted victim VM running OpenSSH. Using FFS, we exemplify end-to-end attacks breaking OpenSSH public-key authentication, and forging GPG signatures from trusted keys, thereby compromising the Ubuntu/Debian update mechanism. We conclude by discussing mitigations and future directions for FFS attacks.

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