<blockquote>
<p><strong>What am I missing?</strong></p>
</blockquote>
<p><a href="https://bitcoin.stackexchange.com/q/92974/13866">What is the length of largest known reorganization in bitcoin?</a></p>
<blockquote>
<p>There have been only two large re-orgs in Bitcoin's history. The first is the value overflow incident in August 2010 that caused a re-org of 53 blocks and the March 12, 2013 fork that caused a re-org of 24 blocks.</p>
</blockquote>
<p>There may be a future need for a reorg of more than 6 blocks?</p>
<p>The alternatives may include the forking and fragmentation of Bitcoin, possibly leading to failure.</p>
<p>At the very least, anyone proposing this sort of change ought to be expected to provide a thorough mathematical and statistical analysis of <em>all</em> previous reorgs and how their proposal would have affected outcomes.</p>
<hr />
<p>Related?</p>
<ul>
<li><a href="https://dspace.mit.edu/handle/1721.1/127476" rel="nofollow noreferrer">An Empirical Analysis of Chain Reorganizations and Double-Spend
Attacks on Proof-of-Work Cryptocurrencies, by
James Peter Thomas Lovejoy S.B. Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 2019</a></li>
</ul>

CC BY-SA 4.0
2021-07-01T10:16:46.983Z
Thank you. I will do some reading.
Alex Macx
CC BY-SA 4.0
2021-07-01T10:40:40.110Z
Turns out Bitcoin Cash ABC did this, or something like this. Here's a helpful BitMEX analysis, which was linked from the paper you linked https://blog.bitmex.com/bitcoin-cash-abcs-rolling-10-block-checkpoints/
Alex Macx
CC BY-SA 4.0
2021-07-01T09:41:05.227Z
2021-07-01T09:55:26.503Z
2021-07-01T09:55:26.503Z
RedGrittyBrick
<p>I have a noob idea and I want to understand where I'm going wrong :)</p>
<p>Say nodes agreed on a block revision limit, say, 6. This would mean that if they see an incoming chain that is longer than the previous longest chain they have seen, they would reject it if it involved changes in blocks further back than 6 blocks ago on their previous longest chain.</p>
<p>If vendors then required 6 confirmations before delivering purchased product, they could be sure that the majority-agreed chain will not be revised to double spend the BTC used to purchase that product. This would protect against a 51% attack.</p>
<p>What am I missing?</p>

<blockchain><full-node><doublespend><consensus><majority-attack>
Noob question: Why is there not a limit of the number of blocks in a chain revision?
Alex Macx
# Noob question: Why is there not a limit of the number of blocks in a chain revision?

(Asked by: username_0 on 2021-07-01)

I have a noob idea and I want to understand where I'm going wrong :)

Say nodes agreed on a block revision limit, say, 6. This would mean that if they see an incoming chain that is longer than the previous longest chain they have seen, they would reject it if it involved changes in blocks further back than 6 blocks ago on their previous longest chain.

If vendors then required 6 confirmations before delivering purchased product, they could be sure that the majority-agreed chain will not be revised to double spend the BTC used to purchase that product. This would protect against a 51% attack.

What am I missing?

**Tags:** blockchain, full-node, doublespend, consensus, majority-attack


---

## 1 answers

### Answer by username_1 on 2021-07-01. Score: 2 | Accepted answer

> **What am I missing?**

[What is the length of largest known reorganization in bitcoin?](https://bitcoin.stackexchange.com/q/92974/13866)

> There have been only two large re-orgs in Bitcoin's history. The first is the value overflow incident in August 2010 that caused a re-org of 53 blocks and the March 12, 2013 fork that caused a re-org of 24 blocks.

There may be a future need for a reorg of more than 6 blocks?

The alternatives may include the forking and fragmentation of Bitcoin, possibly leading to failure.

At the very least, anyone proposing this sort of change ought to be expected to provide a thorough mathematical and statistical analysis of *all* previous reorgs and how their proposal would have affected outcomes.

---

Related?

* [An Empirical Analysis of Chain Reorganizations and Double-Spend
  Attacks on Proof-of-Work Cryptocurrencies, by
  James Peter Thomas Lovejoy S.B. Electrical Engineering and Computer Science, Massachusetts Institute of Technology, 2019](https://dspace.mit.edu/handle/1721.1/127476)

> **Comments:**
> **username_0**: Thank you. I will do some reading.  
> **username_0**: Turns out Bitcoin Cash ABC did this, or something like this. Here's a helpful BitMEX analysis, which was linked from the paper you linked https://blog.bitmex.com/bitcoin-cash-abcs-rolling-10-block-checkpoints/  

---

