<p>A merchant can lessen the risk of being defrauded in a race attack (on 0/unconfirmed) by:</p>

<ul>
<li>Using an explicit list of peers to connect to (with most of the known IP addresses of miners)</li>
<li>Not allowing incoming connections (turn off uPnP)</li>
</ul>

<p>this still leaves the merchant vulnerable to a 51% attack that all transactions below 6 confirmations are subject to but also to the Finney attack and another type of attack even where 2 confirmations is required (as described by vector76 here: <a href="https://bitcointalk.org/index.php?topic=36788.msg463391#msg463391" rel="nofollow noreferrer">https://bitcointalk.org/index.php?topic=36788.msg463391#msg463391</a> )  </p>

<p>What you are asking for is a solution that would be useful for merchants who can absorb some risk that comes with accepting a bitcoin transaction at 0/unconfirmed.  Currently there is only a trivial number of merchants that accept bitcoin at a retail establishment.  And thus, no solution provider -- yet.</p>

<p>There is an API to the service <a href="http://transactionradar.com" rel="nofollow noreferrer">http://transactionradar.com</a> which might make it possible to monitor for double spend attempts.</p>

<p>Some useful conversations related to this topic:</p>

<ul>
<li><a href="http://bitcointalk.org/index.php?topic=36788.0" rel="nofollow noreferrer">http://bitcointalk.org/index.php?topic=36788.0</a></li>
<li><a href="http://bitcointalk.org/index.php?topic=39562.0" rel="nofollow noreferrer">http://bitcointalk.org/index.php?topic=39562.0</a></li>
<li><a href="https://bitcoin.stackexchange.com/questions/722">Has there ever been a successful double spend attack on the Bitcoin network? If not, is it really necessary to wait for confirmations?</a></li>
<li><a href="http://sourceforge.net/mailarchive/message.php?msg_id=27899173" rel="nofollow noreferrer">http://sourceforge.net/mailarchive/message.php?msg_id=27899173</a></li>
<li><a href="http://sourceforge.net/mailarchive/message.php?msg_id=27964471" rel="nofollow noreferrer">http://sourceforge.net/mailarchive/message.php?msg_id=27964471</a></li>
<li><a href="https://bitcoin.stackexchange.com/questions/181/can-bitcoins-be-counterfeited">Can bitcoins be counterfeited?</a></li>
<li><a href="http://bitcointalk.org/index.php?topic=69520" rel="nofollow noreferrer">http://bitcointalk.org/index.php?topic=69520</a></li>
</ul>

CC BY-SA 3.0
2012-01-19T12:28:18.517Z
Thanks for the info and the links. From what I learned it is not possible with the bitcoin client as such because conflicting transactions will not be relayed. Listening to lots of nodes and analyzing their stand like http://transactionradar.com does seems to be what comes closest to detecting conflicting transactions.
kermit
CC BY-SA 3.0
2012-01-18T22:37:02.513Z
2012-03-20T05:23:35.973Z
2017-04-13T12:47:33.583Z
Stephen Gornick
<p>Is there already a way to detect conflicting 0-confirmation transactions? I'm assuming at least one transaction goes to my wallet.</p>

<p>I would expect the client to list the transaction as conflicting but from what I understand from <a href="https://bitcoin.stackexchange.com/questions/730/what-does-the-bitcoin-client-do-when-it-receives-conflicting-transactions">What does the Bitcoin client do when it receives conflicting transactions?</a> it currently does not do so? Is there any other way available?</p>

CC BY-SA 3.0
2012-03-20T05:39:47.260Z
How about conflicting n-confirmation transactions? What does the client do when it finds two heads for the block chain? Any alerts to the user?
Thilo
CC BY-SA 3.0
2012-03-29T07:50:09.817Z
@Thilo: the longest chain always wins. I would expect a block with conflicting transactions to be invalid. Currently there are no user alerts, conflicting transactions will simply not be relayed.
kermit
<transactions><confirmations><fraud>
Is it possible to recognize conflicting 0-confirmation transactions with the Bitcoin client or other available software?
kermit
# Is it possible to recognize conflicting 0-confirmation transactions with the Bitcoin client or other available software?

(Asked by: username_0 on 2012-01-18)

Is there already a way to detect conflicting 0-confirmation transactions? I'm assuming at least one transaction goes to my wallet.

I would expect the client to list the transaction as conflicting but from what I understand from [What does the Bitcoin client do when it receives conflicting transactions?](https://bitcoin.stackexchange.com/questions/730/what-does-the-bitcoin-client-do-when-it-receives-conflicting-transactions) it currently does not do so? Is there any other way available?

**Tags:** transactions, confirmations, fraud

> **Comments:**
> **username_1**: How about conflicting n-confirmation transactions? What does the client do when it finds two heads for the block chain? Any alerts to the user?  
> **username_0**: @username_1: the longest chain always wins. I would expect a block with conflicting transactions to be invalid. Currently there are no user alerts, conflicting transactions will simply not be relayed.  

---

## 1 answers

### Answer by username_2 on 2012-01-18. Score: 2 | Accepted answer

A merchant can lessen the risk of being defrauded in a race attack (on 0/unconfirmed) by:

* Using an explicit list of peers to connect to (with most of the known IP addresses of miners)
* Not allowing incoming connections (turn off uPnP)

this still leaves the merchant vulnerable to a 51% attack that all transactions below 6 confirmations are subject to but also to the Finney attack and another type of attack even where 2 confirmations is required (as described by vector76 here: <https://bitcointalk.org/index.php?topic=36788.msg463391#msg463391> )

What you are asking for is a solution that would be useful for merchants who can absorb some risk that comes with accepting a bitcoin transaction at 0/unconfirmed. Currently there is only a trivial number of merchants that accept bitcoin at a retail establishment. And thus, no solution provider -- yet.

There is an API to the service <http://transactionradar.com> which might make it possible to monitor for double spend attempts.

Some useful conversations related to this topic:

* <http://bitcointalk.org/index.php?topic=36788.0>
* <http://bitcointalk.org/index.php?topic=39562.0>
* [Has there ever been a successful double spend attack on the Bitcoin network? If not, is it really necessary to wait for confirmations?](https://bitcoin.stackexchange.com/questions/722)
* <http://sourceforge.net/mailarchive/message.php?msg_id=27899173>
* <http://sourceforge.net/mailarchive/message.php?msg_id=27964471>
* [Can bitcoins be counterfeited?](https://bitcoin.stackexchange.com/questions/181/can-bitcoins-be-counterfeited)
* <http://bitcointalk.org/index.php?topic=69520>

> **Comments:**
> **username_0**: Thanks for the info and the links. From what I learned it is not possible with the bitcoin client as such because conflicting transactions will not be relayed. Listening to lots of nodes and analyzing their stand like http://transactionradar.com does seems to be what comes closest to detecting conflicting transactions.  

---

