# How probable a 3 compromised Tor relays?

**URL:** https://discuss.privacyguides.net/t/how-probable-a-3-compromised-tor-relays/31104
**Category:** General
**Created:** 2025-09-14T18:28:22Z
**Posts:** 23
**Showing post:** 10 of 23

## Post 10 by @Factorial — 2025-09-18T00:11:36Z

> [@User53](#):
>
> I am not sure if I did the math wrong but it seems to me that 3 compromised Tor relays are not so unlikely.

A more important question is how likely is it that your threat or its allies can purchase data from, or coordinate the efforts of multiple autonomous systems (ASes). For even a nation-state entity running enough tor nodes to consistently de-anonymize users would be troublesome, especially considering guards. But purchasing (or otherwise acquiring) flow data from the ISPs themselves would be much more realistic and effective. And we [already know at least the US government contracts with a cooperation that collects this data in order to deanonymize VPNs.](https://www.404media.co/us-counterintel-buys-netflow-data-team-cymru-track-vpns/) An AS-level adversary, which Tor is not made to counter, does not necessarily have to be a government.

> an adversary can increase her opportunities of per-  
> forming flow correlation by controlling/wiretapping autonomous  
> systems (ASes) or Internet exchange points (IXPs), and record-  
> ing the traffic features of the Tor connections that they transit.  
> Several studies [20 , 49 , 69] demonstrate that specific ASes and  
> IXPs intercept a significant fraction of Tor traffic, therefore are  
> capable of performing flow correlation on Tor at large scale. Oth-  
> ers [18 , 36 , 37, 67 , 69] show that an AS-level adversary can further  
> increase her chances of flow correlation by performing various  
> routing manipulations that reroute a larger fraction of Tor connec-  
> tions through her adversarial ASes and IXPs. For instance, Starov  
> et al. [67] recently show that approximately 40% of Tor circuits are  
> vulnerable to flow correlation attacks by a single malicious AS, and  
> Sun et al. [69] show that churn in BGP as well as active manipula-  
> tion of BGP updates can amplify an adversarial AS’s visibility on  
> Tor connections. This has lead to various proposals on deploying  
> AS-aware path selection mechanisms for Tor
> 
> Source: DeepCorr: Strong Flow Correlation Attacks on Tor  
> Using Deep Learning [https://arxiv.org/pdf/1808.07285](https://arxiv.org/pdf/1808.07285)

> Surprisingly, close to 30% of all relays are hosted in only 6 ASes and 70 prefixes.  
> Together, these relays represent almost 40% of the band-  
> width in the entire Tor network (see Table 5). As such,  
> these few prefixes constitute extremely attractive targets.
> 
> Source: RAPTOR: Routing Attacks on Privacy in Tor [https://www.princeton.edu/~pmittal/publications/raptor-USENIX15.pdf](https://www.princeton.edu/~pmittal/publications/raptor-USENIX15.pdf)

A more in-depth scholarly analysis of this issue can be found here: An Extended View on Measuring Tor AS-level Adversaries [https://arxiv.org/pdf/2403.08517](https://arxiv.org/pdf/2403.08517)

Also see my posts here: [PSA: VPNs can and probably do compromise your privacy - #13 by Factorial](https://discuss.privacyguides.net/t/psa-vpns-can-and-probably-do-compromise-your-privacy/30892/13)

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A special note about guard relays. Guards rotate approximately every few months, which puts a hard cap on the chance of being fully deanonymized for every guard rotation period. But what’s kind of alarming is that as [50.8% of guard probability comes from just 7 ASes](https://metrics.torproject.org/rs.html#aggregate/as/flag:guard%2520).

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So all of this depends on your threat model. If your threat is a western government that’s willing to involve its intelligence agencies to deanonymize your traffic, I would assume that said threat could probably correlate traffic from hundreds of Tor nodes at a minimum, primarily focused on the most popular German guard and exit nodes. I would guess that picking a guard node in a very unpopular and not western-aligned AS, using a undiscovered bridge, or [using Snowflake](https://snowflake.torproject.org/) would help mitigate the possibility of being deanonymized by an AS-level threat.

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