<p><strong>Connecting to the <em>bitcoin network</em> over TOR  to make transactions as an user is a good practice</strong> (this is important to mention in case casual users misunderstand your question).</p>
<p><strong>Running a full bitcoin node exclusively over TOR</strong> can lead to an <a href="https://bitcoin.stackexchange.com/questions/61151/eclipse-attack-vs-sybil-attack">eclipse attack</a> performed by an adversary that controls enough TOR nodes.</p>
<p>This problem is not exclusive to TOR, and occurs in any scenario where an adversary controls a significant portion of the network (such as in countries where internet access is tightly controlled by the government).</p>
<blockquote>
<p>What is it about Tor that makes eclipse attacks trivial?</p>
</blockquote>
<p>It's not exactly trivial. The <a href="https://arxiv.org/abs/1410.6079" rel="noreferrer">Bitcoin Over Tor Isn’t a Good Idea</a> paper estimated that to get a 7% chance to perform an attack, it would cost 2500 USD per month. The cost is possibly higher today.</p>
<p>This type of attack can only be performed (at high probability) by entities with large financial resources,  such as governments.</p>
<p><strong>Avoiding eclipse attacks</strong> is not hard. Make sure that you:</p>
<ul>
<li>Connect to a diverse / trusted list of nodes or</li>
<li>Connect over multiple different networks (for example, you can also <a href="https://bitcoin.stackexchange.com/questions/103402/how-can-i-use-bitcoin-core-with-the-anonymous-network-protocol-i2p">use I2P</a> or the clearnet)</li>
</ul>

CC BY-SA 4.0
2022-11-28T09:45:16.683Z
2022-11-28T09:46:33.103Z
2022-11-28T09:46:33.103Z
bitcoiner2680
<p>There is a good summary of this problem on the <a href="https://bip324.com/" rel="noreferrer">BIP324 website</a>:</p>
<blockquote>
<p>Proxy networks like Tor or I2P introduce a separate address space,
independent from network topology, with a very low cost per address
making eclipse attacks cheaper. In comparison, clearnet IPv4 and IPv6
networks make obtaining multiple network identities in distinct,
well-known network partitions carry a non-trivial cost.</p>
</blockquote>
<p>There is also a paper titled <a href="https://arxiv.org/abs/1410.6079" rel="noreferrer">Bitcoin Over Tor Isn’t a Good Idea</a> that goes into much more detail.</p>

CC BY-SA 4.0
2022-11-28T18:19:43.473Z
@1440000bytes I am not sure I understand your comment, can you elaborate?
Vojtěch Strnad
CC BY-SA 4.0
2022-11-28T18:42:42.910Z
I assume that @1440000bytes means to say this post qualifies as a link-only answer. It does not, though, because Vojtěch included the relevant parts of the linked source and thus the post answers the question by itself even if the link stopped working eventually.—Have an upvote.
Murch
CC BY-SA 4.0
2022-11-28T19:33:38.680Z
I'm not sure whether this is a request to elaborate, but a post that concisely answers the question and links to further pertinent resources is supremely helpful. Less useful posts would e.g. only consist of a link without answering the question, provide a copious medley of tangentially related information widely circling the question without addressing it specifically, or link to a ragbag of peripherally related information that the interested reader first has to sift through to learn anything about the topic at hand.—Sometimes, less is more. Hope that helped.
Murch
CC BY-SA 4.0
2022-11-28T19:59:51.947Z
I don't think those situations are particularly alike, and I have already explained above some of the key differences. Given the results of the respective posts, I do not think my assessment for either are outliers.
Murch
CC BY-SA 4.0
2022-11-28T20:43:43.100Z
Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/140915/discussion-between-murch-and-1440000bytes).
Murch
CC BY-SA 4.0
2022-11-27T12:58:59.330Z
2022-11-27T12:58:59.330Z
Vojtěch Strnad
<p>I've heard that a bitcoin node with only Tor connections is &quot;trivial&quot; to eclipse attack and that such nodes should maintain at least one (or more?) clearnet connections in addition. What is it about Tor that makes eclipse attacks trivial?</p>

<network><tor><eclipse-attack>
Why is connecting bitcoin exclusively over Tor considered bad practice?
pinhead
# Why is connecting bitcoin exclusively over Tor considered bad practice?

(Asked by: username_0 on 2022-11-27)

I've heard that a bitcoin node with only Tor connections is "trivial" to eclipse attack and that such nodes should maintain at least one (or more?) clearnet connections in addition. What is it about Tor that makes eclipse attacks trivial?

**Tags:** network, tor, eclipse-attack


---

## 2 answers

### Answer by username_2 on 2022-11-27. Score: 10 | Accepted answer

There is a good summary of this problem on the [BIP324 website](https://bip324.com/):

> Proxy networks like Tor or I2P introduce a separate address space,
> independent from network topology, with a very low cost per address
> making eclipse attacks cheaper. In comparison, clearnet IPv4 and IPv6
> networks make obtaining multiple network identities in distinct,
> well-known network partitions carry a non-trivial cost.

There is also a paper titled [Bitcoin Over Tor Isn’t a Good Idea](https://arxiv.org/abs/1410.6079) that goes into much more detail.

> **Comments:**
> **username_2**: @1440000bytes I am not sure I understand your comment, can you elaborate?  
> **username_3**: I assume that @1440000bytes means to say this post qualifies as a link-only answer. It does not, though, because username_2 included the relevant parts of the linked source and thus the post answers the question by itself even if the link stopped working eventually.—Have an upvote.  
> **username_3**: I'm not sure whether this is a request to elaborate, but a post that concisely answers the question and links to further pertinent resources is supremely helpful. Less useful posts would e.g. only consist of a link without answering the question, provide a copious medley of tangentially related information widely circling the question without addressing it specifically, or link to a ragbag of peripherally related information that the interested reader first has to sift through to learn anything about the topic at hand.—Sometimes, less is more. Hope that helped.  
> **username_3**: I don't think those situations are particularly alike, and I have already explained above some of the key differences. Given the results of the respective posts, I do not think my assessment for either are outliers.  
> **username_3**: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/140915/discussion-between-username_3-and-1440000bytes).  

---

### Answer by username_1 on 2022-11-28. Score: 10

**Connecting to the *bitcoin network* over TOR to make transactions as an user is a good practice** (this is important to mention in case casual users misunderstand your question).

**Running a full bitcoin node exclusively over TOR** can lead to an [eclipse attack](https://bitcoin.stackexchange.com/questions/61151/eclipse-attack-vs-sybil-attack) performed by an adversary that controls enough TOR nodes.

This problem is not exclusive to TOR, and occurs in any scenario where an adversary controls a significant portion of the network (such as in countries where internet access is tightly controlled by the government).

> What is it about Tor that makes eclipse attacks trivial?

It's not exactly trivial. The [Bitcoin Over Tor Isn’t a Good Idea](https://arxiv.org/abs/1410.6079) paper estimated that to get a 7% chance to perform an attack, it would cost 2500 USD per month. The cost is possibly higher today.

This type of attack can only be performed (at high probability) by entities with large financial resources, such as governments.

**Avoiding eclipse attacks** is not hard. Make sure that you:

* Connect to a diverse / trusted list of nodes or
* Connect over multiple different networks (for example, you can also [use I2P](https://bitcoin.stackexchange.com/questions/103402/how-can-i-use-bitcoin-core-with-the-anonymous-network-protocol-i2p) or the clearnet)


---

