Entries Tagged "Tor"

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Illegal Content and the Blockchain

Security researchers have recently discovered a botnet with a novel defense against takedowns. Normally, authorities can disable a botnet by taking over its command-and-control server. With nowhere to go for instructions, the botnet is rendered useless. But over the years, botnet designers have come up with ways to make this counterattack harder. Now the content-delivery network Akamai has reported on a new method: a botnet that uses the Bitcoin blockchain ledger. Since the blockchain is globally accessible and hard to take down, the botnet’s operators appear to be safe.

It’s best to avoid explaining the mathematics of Bitcoin’s blockchain, but to understand the colossal implications here, you need to understand one concept. Blockchains are a type of “distributed ledger”: a record of all transactions since the beginning, and everyone using the blockchain needs to have access to — and reference — a copy of it. What if someone puts illegal material in the blockchain? Either everyone has a copy of it, or the blockchain’s security fails.

To be fair, not absolutely everyone who uses a blockchain holds a copy of the entire ledger. Many who buy cryptocurrencies like Bitcoin and Ethereum don’t bother using the ledger to verify their purchase. Many don’t actually hold the currency outright, and instead trust an exchange to do the transactions and hold the coins. But people need to continually verify the blockchain’s history on the ledger for the system to be secure. If they stopped, then it would be trivial to forge coins. That’s how the system works.

Some years ago, people started noticing all sorts of things embedded in the Bitcoin blockchain. There are digital images, including one of Nelson Mandela. There’s the Bitcoin logo, and the original paper describing Bitcoin by its alleged founder, the pseudonymous Satoshi Nakamoto. There are advertisements, and several prayers. There’s even illegal pornography and leaked classified documents. All of these were put in by anonymous Bitcoin users. But none of this, so far, appears to seriously threaten those in power in governments and corporations. Once someone adds something to the Bitcoin ledger, it becomes sacrosanct. Removing something requires a fork of the blockchain, in which Bitcoin fragments into multiple parallel cryptocurrencies (and associated blockchains). Forks happen, rarely, but never yet because of legal coercion. And repeated forking would destroy Bitcoin’s stature as a stable(ish) currency.

The botnet’s designers are using this idea to create an unblockable means of coordination, but the implications are much greater. Imagine someone using this idea to evade government censorship. Most Bitcoin mining happens in China. What if someone added a bunch of Chinese-censored Falun Gong texts to the blockchain?<

What if someone added a type of political speech that Singapore routinely censors? Or cartoons that Disney holds the copyright to?

In Bitcoin’s and most other public blockchains there are no central, trusted authorities. Anyone in the world can perform transactions or become a miner. Everyone is equal to the extent that they have the hardware and electricity to perform cryptographic computations.

This openness is also a vulnerability, one that opens the door to asymmetric threats and small-time malicious actors. Anyone can put information in the one and only Bitcoin blockchain. Again, that’s how the system works.

Over the last three decades, the world has witnessed the power of open networks: blockchains, social media, the very web itself. What makes them so powerful is that their value is related not just to the number of users, but the number of potential links between users. This is Metcalfe’s law — value in a network is quadratic, not linear, in the number of users — and every open network since has followed its prophecy.

As Bitcoin has grown, its monetary value has skyrocketed, even if its uses remain unclear. With no barrier to entry, the blockchain space has been a Wild West of innovation and lawlessness. But today, many prominent advocates suggest Bitcoin should become a global, universal currency. In this context, asymmetric threats like embedded illegal data become a major challenge.

The philosophy behind Bitcoin traces to the earliest days of the open internet. Articulated in John Perry Barlow’s 1996 Declaration of the Independence of Cyberspace, it was and is the ethos of tech startups: Code is more trustworthy than institutions. Information is meant to be free, and nobody has the right — and should not have the ability — to control it.

But information must reside somewhere. Code is written by and for people, stored on computers located within countries, and embedded within the institutions and societies we have created. To trust information is to trust its chain of custody and the social context it comes from. Neither code nor information is value-neutral, nor ever free of human context.

Today, Barlow’s vision is a mere shadow; every society controls the information its people can access. Some of this control is through overt censorship, as China controls information about Taiwan, Tiananmen Square, and the Uyghurs. Some of this is through civil laws designed by the powerful for their benefit, as with Disney and US copyright law, or UK libel law.

Bitcoin and blockchains like it are on a collision course with these laws. What happens when the interests of the powerful, with the law on their side, are pitted against an open blockchain? Let’s imagine how our various scenarios might play out.

China first: In response to Falun Gong texts in the blockchain, the People’s Republic decrees that any miners processing blocks with banned content will be taken offline — their IPs will be blacklisted. This causes a hard fork of the blockchain at the point just before the banned content. China might do this under the guise of a “patriotic” messaging campaign, publicly stating that it’s merely maintaining financial sovereignty from Western banks. Then it uses paid influencers and moderators on social media to pump the China Bitcoin fork, through both partisan comments and transactions. Two distinct forks would soon emerge, one behind China’s Great Firewall and one outside. Other countries with similar governmental and media ecosystems — Russia, Singapore, Myanmar — might consider following suit, creating multiple national Bitcoin forks. These would operate independently, under mandates to censor unacceptable transactions from then on.

Disney’s approach would play out differently. Imagine the company announces it will sue any ISP that hosts copyrighted content, starting with networks hosting the biggest miners. (Disney has sued to enforce its intellectual property rights in China before.) After some legal pressure, the networks cut the miners off. The miners reestablish themselves on another network, but Disney keeps the pressure on. Eventually miners get pushed further and further off of mainstream network providers, and resort to tunneling their traffic through an anonymity service like Tor. That causes a major slowdown in the already slow (because of the mathematics) Bitcoin network. Disney might issue takedown requests for Tor exit nodes, causing the network to slow to a crawl. It could persist like this for a long time without a fork. Or the slowdown could cause people to jump ship, either by forking Bitcoin or switching to another cryptocurrency without the copyrighted content.

And then there’s illegal pornographic content and leaked classified data. These have been on the Bitcoin blockchain for over five years, and nothing has been done about it. Just like the botnet example, it may be that these do not threaten existing power structures enough to warrant takedowns. This could easily change if Bitcoin becomes a popular way to share child sexual abuse material. Simply having these illegal images on your hard drive is a felony, which could have significant repercussions for anyone involved in Bitcoin.

Whichever scenario plays out, this may be the Achilles heel of Bitcoin as a global currency.

If an open network such as a blockchain were threatened by a powerful organization — China’s censors, Disney’s lawyers, or the FBI trying to take down a more dangerous botnet — it could fragment into multiple networks. That’s not just a nuisance, but an existential risk to Bitcoin.

Suppose Bitcoin were fragmented into 10 smaller blockchains, perhaps by geography: one in China, another in the US, and so on. These fragments might retain their original users, and by ordinary logic, nothing would have changed. But Metcalfe’s law implies that the overall value of these blockchain fragments combined would be a mere tenth of the original. That is because the value of an open network relates to how many others you can communicate with — and, in a blockchain, transact with. Since the security of bitcoin currency is achieved through expensive computations, fragmented blockchains are also easier to attack in a conventional manner — through a 51 percent attack — by an organized attacker. This is especially the case if the smaller blockchains all use the same hash function, as they would here.

Traditional currencies are generally not vulnerable to these sorts of asymmetric threats. There are no viable small-scale attacks against the US dollar, or almost any other fiat currency. The institutions and beliefs that give money its value are deep-seated, despite instances of currency hyperinflation.

The only notable attacks against fiat currencies are in the form of counterfeiting. Even in the past, when counterfeit bills were common, attacks could be thwarted. Counterfeiters require specialized equipment and are vulnerable to law enforcement discovery and arrest. Furthermore, most money today — even if it’s nominally in a fiat currency — doesn’t exist in paper form.

Bitcoin attracted a following for its openness and immunity from government control. Its goal is to create a world that replaces cultural power with cryptographic power: verification in code, not trust in people. But there is no such world. And today, that feature is a vulnerability. We really don’t know what will happen when the human systems of trust come into conflict with the trustless verification that make blockchain currencies unique. Just last week we saw this exact attack on smaller blockchains — not Bitcoin yet. We are watching a public socio-technical experiment in the making, and we will witness its success or failure in the not-too-distant future.

This essay was written with Barath Raghavan, and previously appeared on Wired.com.

Posted on March 17, 2021 at 6:10 AMView Comments

Digital Security Exchange: Security for High-Risk Communities

I am part of this very interesting project:

For many users, blog posts on how to install Signal, massive guides to protecting your digital privacy, and broad statements like “use Tor” — all offered in good faith and with the best of intentions — can be hard to understand or act upon. If we want to truly secure civil society from digital attacks and empower communities in their to fight to protect their rights, we’ve got to recognize that digital security is largely a human problem, not a technical one. Taking cues from the experiences of the deeply knowledgeable global digital security training community, the Digital Security Exchange will seek to make it easier for trainers and experts to connect directly to the communities in the U.S. — sharing expertise, documentation, and best practices — in order to increase capacity and security across the board.

Posted on March 14, 2017 at 1:08 PMView Comments

Researchers Discover Tor Nodes Designed to Spy on Hidden Services

Two researchers have discovered over 100 Tor nodes that are spying on hidden services. Cory Doctorow explains:

These nodes — ordinary nodes, not exit nodes — sorted through all the traffic that passed through them, looking for anything bound for a hidden service, which allowed them to discover hidden services that had not been advertised. These nodes then attacked the hidden services by making connections to them and trying common exploits against the server-software running on them, seeking to compromise and take them over.

The researchers used “honeypot” .onion servers to find the spying computers: these honeypots were .onion sites that the researchers set up in their own lab and then connected to repeatedly over the Tor network, thus seeding many Tor nodes with the information of the honions’ existence. They didn’t advertise the honions’ existence in any other way and there was nothing of interest at these sites, and so when the sites logged new connections, the researchers could infer that they were being contacted by a system that had spied on one of their Tor network circuits.

This attack was already understood as a theoretical problem for the Tor project, which had recently undertaken a rearchitecting of the hidden service system that would prevent it from taking place.

No one knows who is running the spying nodes: they could be run by criminals, governments, private suppliers of “infowar” weapons to governments, independent researchers, or other scholars (though scholarly research would not normally include attempts to hack the servers once they were discovered).

The Tor project is working on redesigning its system to block this attack.

Vice Motherboard article. Defcon talk announcement.

Posted on July 8, 2016 at 7:01 AMView Comments

Did Carnegie Mellon Attack Tor for the FBI?

There’s pretty strong evidence that the team of researchers from Carnegie Mellon University who cancelled their scheduled 2015 Black Hat talk deanonymized Tor users for the FBI.

Details are in this Vice story and this Wired story (and these two follow-on Vice stories). And here’s the reaction from the Tor Project.

Nicholas Weaver guessed this back in January.

The behavior of the researchers is reprehensible, but the real issue is that CERT Coordination Center (CERT/CC) has lost its credibility as an honest broker. The researchers discovered this vulnerability and submitted it to CERT. Neither the researchers nor CERT disclosed this vulnerability to the Tor Project. Instead, the researchers apparently used this vulnerability to deanonymize a large number of hidden service visitors and provide the information to the FBI.

Does anyone still trust CERT to behave in the Internet’s best interests?

EDITED TO ADD (12/14): I was wrong. CERT did disclose to Tor.

Posted on November 16, 2015 at 6:19 AMView Comments

Anonymous Browsing at the Library

A rural New Hampshire library decided to install Tor on their computers and allow anonymous Internet browsing. The Department of Homeland pressured them to stop:

A special agent in a Boston DHS office forwarded the article to the New Hampshire police, who forwarded it to a sergeant at the Lebanon Police Department.

DHS spokesman Shawn Neudauer said the agent was simply providing “visibility/situational awareness,” and did not have any direct contact with the Lebanon police or library. “The use of a Tor browser is not, in [or] of itself, illegal and there are legitimate purposes for its use,” Neudauer said, “However, the protections that Tor offers can be attractive to criminal enterprises or actors and HSI [Homeland Security Investigations] will continue to pursue those individuals who seek to use the anonymizing technology to further their illicit activity.”

When the DHS inquiry was brought to his attention, Lt. Matthew Isham of the Lebanon Police Department was concerned. “For all the good that a Tor may allow as far as speech, there is also the criminal side that would take advantage of that as well,” Isham said. “We felt we needed to make the city aware of it.”

The good news is that the library is resisting the pressure and keeping Tor running.

This is an important issue for reasons that go beyond the New Hampshire library. The goal of the Library Freedom Project is to set up Tor exit nodes at libraries. Exit nodes help every Tor user in the world; the more of them there are, the harder it is to subvert the system. The Kilton Public Library isn’t just allowing its patrons to browse the Internet anonymously; it is helping dissidents around the world stay alive.

Librarians have been protecting our privacy for decades, and I’m happy to see that tradition continue.

EDITED TO ADD (10/13): As a result of the story, more libraries are planning to run Tor nodes.

Posted on September 16, 2015 at 1:40 PMView Comments

Bizarre High-Tech Kidnapping

This is a story of a very high-tech kidnapping:

FBI court filings unsealed last week showed how Denise Huskins’ kidnappers used anonymous remailers, image sharing sites, Tor, and other people’s Wi-Fi to communicate with the police and the media, scrupulously scrubbing meta data from photos before sending. They tried to use computer spyware and a DropCam to monitor the aftermath of the abduction and had a Parrot radio-controlled drone standing by to pick up the ransom by remote control.

The story also demonstrates just how effective the FBI is tracing cell phone usage these days. They had a blocked call from the kidnappers to the victim’s cell phone. First they used a search warrant to AT&T to get the actual calling number. After learning that it was an AT&T prepaid Tracfone, they called AT&T to find out where the burner was bought, what the serial numbers were, and the location where the calls were made from.

The FBI reached out to Tracfone, which was able to tell the agents that the phone was purchased from a Target store in Pleasant Hill on March 2 at 5:39 pm. Target provided the bureau with a surveillance-cam photo of the buyer: a white male with dark hair and medium build. AT&T turned over records showing the phone had been used within 650 feet of a cell site in South Lake Tahoe.

Here’s the criminal complaint. It borders on surreal. Were it an episode of CSI:Cyber, you would never believe it.

Posted on July 29, 2015 at 6:34 AMView Comments

Using Secure Chat

Micah Lee has a good tutorial on installing and using secure chat.

To recap: We have installed Orbot and connected to the Tor network on Android, and we have installed ChatSecure and created an anonymous secret identity Jabber account. We have added a contact to this account, started an encrypted session, and verified that their OTR fingerprint is correct. And now we can start chatting with them with an extraordinarily high degree of privacy.

FBI Director James Comey, UK Prime Minister David Cameron, and totalitarian governments around the world all don’t want you to be able to do this.

Posted on July 17, 2015 at 6:35 AMView Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.