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Does Tor provide more benefit or harm? New paper says it depends

The Tor anonymity network has generated controversy almost constantly since its inception almost two decades ago. Supporters say it’s a vital service for protecting online privacy and circumventing censorship, particularly in countries with poor human rights records. Critics, meanwhile, argue that Tor shields criminals distributing child-abuse images, trafficking in illegal drugs, and engaging in other illicit activities.

Researchers on Monday unveiled new estimates that attempt to measure the potential harms and benefits of Tor. They found that, worldwide, almost 7 percent of Tor users connect to hidden services, which the researchers contend are disproportionately more likely to offer illicit services or content compared with normal Internet sites. Connections to hidden services were significantly higher in countries rated as more politically “free” relative to those that are “partially free” or “not free.”

Licit versus illicit

Specifically, the fraction of Tor users globally accessing hidden sites is 6.7, a relatively small proportion. Those users, however, aren’t evenly distributed geographically. In countries with regimes rated “not free” by this scoring from an organization called Freedom House, access to hidden services was just 4.8 percent. In “free” countries, the proportion jumped to 7.8 percent.

Here’s a graph of the breakdown:

More politically “free” countries have higher proportions of Hidden Services traffic than is present in either “partially free” or “not free” nations. Each point indicates the average daily percentage of anonymous services accessed in a given country. The white regions represent the kernel density distributions for each ordinal category of political freedom (“free,” “partially free,” and “not free”Enlarge / More politically “free” countries have higher proportions of Hidden Services traffic than is present in either “partially free” or “not free” nations. Each point indicates the average daily percentage of anonymous services accessed in a given country. The white regions represent the kernel density distributions for each ordinal category of political freedom (“free,” “partially free,” and “not free”

In a paper, the researchers wrote:

The Tor anonymity network can be used for both licit and illicit purposes. Our results provide a clear, if probabilistic, estimation of the extent to which users of Tor engage in either form of activity. Generally, users of Tor in politically “free” countries are significantly more likely to be using the network in likely illicit ways. A host of additional questions remain, given the anonymous nature of Tor and other similar systems such as I2P and Freenet. Our results narrowly suggest, however, users of Tor in more repressive “not free” regimes tend to be far more likely to venture via the Tor network to Clear Web content and so are comparatively less likely to be engaged in activities that would be widely deemed malicious.

The estimates are based on a sample comprising 1 percent of Tor entry nodes, which the researchers monitored from December 31, 2018, to August 18, 2019, with an interruption to data collection from May 4 to May 13. By analyzing directory lookups and other unique signatures in the traffic, the researchers distinguished when a Tor client was visiting normal Internet websites or anonymous (or Dark Web) services.


The researchers—from Virginia Tech in Blacksburg, Virginia; Skidmore College in Saratoga Springs, New York; and Cyber Espion in Portsmouth, United Kingdom—acknowledged that the estimates aren’t perfect, In part, that’s because the estimates are based on the unprovable assumption that the overwhelming majority of Dark Web sites provide illicit content or services.

The paper, however, argues that the findings can be useful for policymakers who are trying to gauge the benefits of Tor relative to the harms it creates. The researchers view the results through the lenses of the 2015 paper titled The Dark Web Dilemma: Tor, Anonymity and Online Policing and On Liberty, the essay published by English philosopher John Stuart Mill in 1859.

Dark Web dilemma

The researchers in Monday’s paper wrote:

These results have a number of consequences for research and policy. First, the results suggest that anonymity-granting technologies such as Tor present a clear public policy challenge and include clear political context and geographical components. This policy challenge is referred to in the literature as the “Dark Web dilemma.” At the root of the dilemma is the so-called “harm principle” proposed in On Liberty by John Stuart Mill. In this principle, it is morally permissible to undertake any action so long as it does not cause someone else harm.

The challenge of the Tor anonymity network, as intimated by its dual use nature, is that maximal policy solutions all promise to cause harm to some party. Leaving the Tor network up and free from law enforcement investigation is likely to lead to direct and indirect harms that result from the system being used by those engaged in child exploitation, drug exchange, and the sale of firearms, although these harms are of course highly heterogeneous in terms of their potential negative social impacts and some, such as personal drug use, might also have predominantly individual costs in some cases.

Conversely, simply working to shut down Tor would cause harm to dissidents and human rights activists, particularly, our results suggest, in more repressive, less politically free regimes where technological protections are often needed the most.

Our results showing the uneven distribution of likely licit and illicit users of Tor across countries also suggest that there may be a looming public policy conflagration on the horizon. The Tor network, for example, runs on ∼6,000–6,500 volunteer nodes. While these nodes are distributed across a number of countries, it is plausible that many of these infrastructural points cluster in politically free liberal democratic countries. Additionally, the Tor Project, which manages the code behind the network, is an incorporated not for profit in the United States and traces both its intellectual origins and a large portion of its financial resources to the US government.

In other words, much of the physical and protocol infrastructure of the Tor anonymity network is clustered disproportionately in free regimes, especially the United States. Linking this trend with a strict interpretation of our current results suggests that the harms from the Tor anonymity network cluster in free countries hosting the infrastructure of Tor and that the benefits cluster in disproportionately highly repressive regimes.

A “flawed” assumption

It didn’t take long for people behind the Tor Project to question the findings and the assumptions that led to them. In an email, Isabela Bagueros, executive director of the Tor Project, wrote:


The authors of this research paper have chosen to categorize all .onion sites and all traffic to these sites as “illicit” and all traffic on the “Clear Web” as ‘licit.’

This assumption is flawed. Many popular websites, tools, and services use onion services to offer privacy and censorship-circumvention benefits to their users. For example, Facebook offers an onion service. Global news organizations, including The New York Times, BBC, Deutsche Welle, Mada Masr, and Buzzfeed, offer onion services.

Whistleblowing platforms, filesharing tools, messaging apps, VPNs, browsers, email services, and free software projects also use onion services to offer privacy protections to their users, including Riseup, OnionShare, SecureDrop, GlobaLeaks, ProtonMail, Debian, Mullvad VPN, Ricochet Refresh, Briar, and Qubes OS.

(For even more examples, and quotes from website admins that use onion services on why they use Tor:

Writing off traffic to these widely-used sites and services as “illicit” is a generalization that demonizes people and organizations who choose technology that allows them to protect their privacy and circumvent censorship. In a world of increasing surveillance capitalism and internet censorship, online privacy is necessary for many of us to exercise our human rights to freely access information, share our ideas, and communicate with one another. Incorrectly identifying all onion service traffic as “illicit” harms the fight to protect encryption and benefits the powers that be that are trying to weaken or entirely outlaw strong privacy technology.

Secondly, we look forward to hearing the researchers describe their methodology in more detail, so the scientific community has the possibility to assess whether their approach is accurate and safe. The copy of the paper provided does not outline their methodology, so there is no way for the Tor Project or other researchers to assess the accuracy of their findings.

The paper is unlikely to convert Tor supporters to critics or vice versa. It does, however, provide a timely estimate of overall Tor usage and geographic breakdown that will be of interest to many policymakers.

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