<p>When you have open-source software, it's a fine line between "configuring" and "writing". </p>

<p>Say you want to reject all attempts to spend a particular transaction. There isn't a command-line option or config file directive to do this in the standard Bitcoin Core distribution, so in that sense the answer is "no". But you can do it by adding two obvious lines of source code and recompiling, which is only marginally work than modifying a config file. </p>

<p>There is certainly no need to rewrite Bitcoin Core from scratch, if that's what you're asking.  You can assume that if anyone is planning a 51% attack, the need to modify software is not going to be a significant obstacle.</p>

CC BY-SA 3.0
2017-04-21T19:49:41.660Z
2017-04-21T19:49:41.660Z
Nate Eldredge
<blockquote>
  <p>I know that it would cost hundreds of millions of dollars to do a 51% attack on Bitcoin</p>
</blockquote>

<p>wrong</p>

<blockquote>
  <p>or would such an attacker need to write their own software?</p>
</blockquote>

<p>no new software/hardware is needed.</p>

CC BY-SA 3.0
2017-04-21T09:59:33.067Z
Please elaborate. Yes/no answers are not very informative.
Pieter Wuille
CC BY-SA 3.0
2017-04-21T10:56:26.527Z
I do not understand how should I describe the software, **which is not needed** to perform some job. :)  OK, in fact you have to have mining pool software and enough miners connected to your pool. Creating the pool costs less than "hundred millions"? isn't it obvious?
amaclin
CC BY-SA 3.0
2017-04-21T10:58:52.217Z
If it was obvious, OP wouldn't have asked the question. You're not being helpful.
Pieter Wuille
CC BY-SA 3.0
2017-04-21T12:20:52.933Z
Sometimes it is useful to ask obvious questions just to prove to yourself that everyone has the same thoughts.
amaclin
CC BY-SA 3.0
2017-06-20T23:00:48.397Z
Such things deserve to be comments or requests for clarifications. Not answers.
Pieter Wuille
CC BY-SA 3.0
2017-04-21T07:51:23.583Z
2017-04-21T07:51:23.583Z
amaclin
<p>I know that it would cost hundreds of millions of dollars to do a 51% attack on Bitcoin, but if somebody did that, bought the hardware, etc could Bitcoin Core or any other software be easily configured to do what they want (e.g, ignore blocks containing a certain transaction in order to try to get rid of it), or would such an attacker need to write their own software?</p>

CC BY-SA 3.0
2017-04-21T03:22:29.563Z
If you're already paying hundreds of millions for mining hardware, paying some programmer to hack up a bitcoin node to do what you want, is literally small change.
Greg Hewgill
<bitcoin-core><client><attack><majority-attack>
Does the software to conduct a 51% attack exist?
markasoftware
# Does the software to conduct a 51% attack exist?

(Asked by: username_0 on 2017-04-21)

I know that it would cost hundreds of millions of dollars to do a 51% attack on Bitcoin, but if somebody did that, bought the hardware, etc could Bitcoin Core or any other software be easily configured to do what they want (e.g, ignore blocks containing a certain transaction in order to try to get rid of it), or would such an attacker need to write their own software?

**Tags:** bitcoin-core, client, attack, majority-attack

> **Comments:**
> **username_1**: If you're already paying hundreds of millions for mining hardware, paying some programmer to hack up a bitcoin node to do what you want, is literally small change.  

---

## 2 answers

### Answer by username_2 on 2017-04-21. Score: 1

When you have open-source software, it's a fine line between "configuring" and "writing".

Say you want to reject all attempts to spend a particular transaction. There isn't a command-line option or config file directive to do this in the standard Bitcoin Core distribution, so in that sense the answer is "no". But you can do it by adding two obvious lines of source code and recompiling, which is only marginally work than modifying a config file.

There is certainly no need to rewrite Bitcoin Core from scratch, if that's what you're asking. You can assume that if anyone is planning a 51% attack, the need to modify software is not going to be a significant obstacle.


---

### Answer by username_3 on 2017-04-21. Score: -2

> I know that it would cost hundreds of millions of dollars to do a 51% attack on Bitcoin

wrong

> or would such an attacker need to write their own software?

no new software/hardware is needed.

> **Comments:**
> **username_4**: Please elaborate. Yes/no answers are not very informative.  
> **username_3**: I do not understand how should I describe the software, **which is not needed** to perform some job. :)  OK, in fact you have to have mining pool software and enough miners connected to your pool. Creating the pool costs less than "hundred millions"? isn't it obvious?  
> **username_4**: If it was obvious, OP wouldn't have asked the question. You're not being helpful.  
> **username_3**: Sometimes it is useful to ask obvious questions just to prove to yourself that everyone has the same thoughts.  
> **username_4**: Such things deserve to be comments or requests for clarifications. Not answers.  

---

