<p>Such an attack is not possible:</p>

<p>The protocol contains a <a href="https://bitcoin.stackexchange.com/questions/5838/how-is-difficulty-calculated">rule how to calculate the difficulty</a> to succeed in mining a new transaction block. This difficulty expresses in the form that a hash must fulfil (<a href="https://bitcoin.stackexchange.com/questions/8806/what-is-difficulty-and-how-it-relates-to-target?rq=1">number of leading zeroes</a>) in order for other network participants to accept it as valid.</p>

<p>There is no other way to arrive faster at a hash that fulfils the difficulty requirements than to try out as many as possible as fast as possible.</p>

<p>Now, you could easily reduce the difficulty requirement in your client's protocol and mine thousands of blocks every second, but these blocks would not be accepted by the other network participants. Firstly, of course, because you don't fulfill the difficulty and secondly, because the length of the blockchain is measured not in the number of blocks, but in the <a href="https://en.bitcoin.it/wiki/Weaknesses#Generate_.22valid.22_blocks_with_a_lower_difficulty_than_normal" rel="nofollow noreferrer">combined difficulty of the blocks</a>.</p>

CC BY-SA 3.0
2013-08-30T17:48:00.973Z
As an analogy, you can say "I declare the US dollar to be a Post-It note with a smiley face drawn on it", and make thousands of them in your own home.  Nobody is stopping you.  But the rest of the world probably won't agree with your definition, and won't accept your "dollars" as payment.
Nate Eldredge
CC BY-SA 3.0
2013-08-30T14:35:00.767Z
2013-08-30T14:35:00.767Z
2017-04-13T12:47:33.610Z
Murch
<p>Is it possible to make changes in Bitcoin protocol and then start to mine faster than 1 block in 10 minutes?</p>

<p>What happens when someone makes those changes and "mines offline" blockchain that is longer than current one. And after that changes protocol back to "normal" and appears back to online network?</p>

<p>Is it even possible?</p>

CC BY-SA 3.0
2013-08-30T14:59:03.780Z
You might want to think of a more descriptive title for your question, perhaps something along the lines of "How does the network defend against protocol change based blockchain attacks?"
Murch
CC BY-SA 3.0
2013-12-06T13:13:24.427Z
This was posted as an answer, but doesn't attempt to answer the question. Please create a new question for your question. You may provide a link there to this question if it helps provide context. Please refer to [ask] or [about] for more information about the concept of Stackexchange.
Murch
<blockchain><security>
Is it possible to change to protocol, mine lots of blocks offline, and then change it back?
stereotyyp
# Is it possible to change to protocol, mine lots of blocks offline, and then change it back?

(Asked by: username_0 on 2013-08-30)

Is it possible to make changes in Bitcoin protocol and then start to mine faster than 1 block in 10 minutes?

What happens when someone makes those changes and "mines offline" blockchain that is longer than current one. And after that changes protocol back to "normal" and appears back to online network?

Is it even possible?

**Tags:** blockchain, security

> **Comments:**
> **username_1**: You might want to think of a more descriptive title for your question, perhaps something along the lines of "How does the network defend against protocol change based blockchain attacks?"  
> **username_1**: This was posted as an answer, but doesn't attempt to answer the question. Please create a new question for your question. You may provide a link there to this question if it helps provide context. Please refer to [ask] or [about] for more information about the concept of Stackexchange.  

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## 1 answers

### Answer by username_1 on 2013-08-30. Score: 5 | Accepted answer

Such an attack is not possible:

The protocol contains a [rule how to calculate the difficulty](https://bitcoin.stackexchange.com/questions/5838/how-is-difficulty-calculated) to succeed in mining a new transaction block. This difficulty expresses in the form that a hash must fulfil ([number of leading zeroes](https://bitcoin.stackexchange.com/questions/8806/what-is-difficulty-and-how-it-relates-to-target?rq=1)) in order for other network participants to accept it as valid.

There is no other way to arrive faster at a hash that fulfils the difficulty requirements than to try out as many as possible as fast as possible.

Now, you could easily reduce the difficulty requirement in your client's protocol and mine thousands of blocks every second, but these blocks would not be accepted by the other network participants. Firstly, of course, because you don't fulfill the difficulty and secondly, because the length of the blockchain is measured not in the number of blocks, but in the [combined difficulty of the blocks](https://en.bitcoin.it/wiki/Weaknesses#Generate_.22valid.22_blocks_with_a_lower_difficulty_than_normal).

> **Comments:**
> **username_2**: As an analogy, you can say "I declare the US dollar to be a Post-It note with a smiley face drawn on it", and make thousands of them in your own home.  Nobody is stopping you.  But the rest of the world probably won't agree with your definition, and won't accept your "dollars" as payment.  

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