<p>First you need to define "reorg". Under the definition I'll use, the minimum reorg is two blocks. The definition would be:
"A reorginization occurs when a block is broadcast with a history that is incompatible with the previously work-heaviest** known blockchain, under the same consensus rules"</p>

<p>Say a block is mined onto the height 593000 block, with hash <code>000000000000000000a11...</code> so that apparently, block 593001 has been found, and many miners are now mining based off of this hash. </p>

<p>Now imagine that someone broadcasts block 593002 with hash <code>000000000000000000c84...</code>but upon examining block 593001, you see that the hash is <code>000000000000000000b5c...</code></p>

<p>A reorg has just taken place. Someone mined block 593001, and without broadcasting it (or perhaps after broadcasting it too late), mined 593002 on top of it. Now any transactions in the block with hash <code>000000000000000000a11...</code> have not been confirmed (one of which was the original miner sending the block reward transaction to themselves), since the (valid) block that contains them has been orphaned.</p>

<p>As far as "how long", a reorg is relative to the observer, so one could technically take place before you observe the original chain at all.</p>

<p>** <em>essentially, the longest chain, but there are exceptions where a "reorg" could be a shorter chain in terms of number of blocks, when a shorter chain contains "more" proof of work. This is outside the scope of this answer.</em></p>

CC BY-SA 4.0
2019-08-28T01:19:21.210Z
so lets assume they want to reorg a 5,300 BTC transaction after 30 days of its creation what is the situation ? if around 100 blocks daily is trying to reorg after 3000 blocks, and here am talking about huge reorging power. i just need to know when there are no chance for reorging to i can gave up the company to them after this time frame from their transaction.
BTC involver
CC BY-SA 4.0
2019-08-28T01:30:39.923Z
The size of the transaction is completely irrelevant. Realistically, waiting for just 1 confirmation will give you an extremely high chance of your transaction being permanent, especially in the absence of double spend attempts, which are trivial to detect. (I am ONLY referring to the Bitcoin blockchain here. All other blockchains have significantly weaker security. This is the advantage of using Bitcoin vs any altcoins)
For sending bitcoin, 2 confirmations is overkill for any realistic scenario.
hedgedandlevered
CC BY-SA 4.0
2019-08-28T01:33:42.520Z
its not irrelevant because if its low the miners wont accept to help them reorging but with a huge reword they would accept, so if they risk 2650 btc as fees to the miners to get net of 2650 btc back? that's my point.
BTC involver
CC BY-SA 4.0
2019-08-28T02:15:37.310Z
No. First, you'd need over 51% of the hashing power to collude to do this, which is essentially impossible to coordinate at all, even if you could convince them. Second, you'd need to convince them to basically break Bitcoin, after they have spent millions of dollars buying specialized equipment that is useless without Bitcoin. And all of this without your counterparty suspecting anything, all for what is essentially still a relatively small tx vs miner rewards (1800 btc are mined daily). It's just not something that would be in anyone's financial interest that had mining machines.
hedgedandlevered
CC BY-SA 4.0
2019-08-28T02:17:51.590Z
and then on top of that, you've only saved yourself bitcoin, which is now nearly worthless in traditional currency terms due to the 51% attack. So you don't even have upside in this ridiculous scenario.
hedgedandlevered
CC BY-SA 4.0
2019-08-28T02:28:25.280Z
do you mean that i should giveup taking it as btc ?
BTC involver
CC BY-SA 4.0
2019-08-28T02:31:14.900Z
could you elaborate? Taking what? Against what alternative?
hedgedandlevered
CC BY-SA 4.0
2019-08-28T02:32:49.753Z
55,000,000 USD or 5,300 BTC. in both cases i will not use the money for years.
BTC involver
CC BY-SA 4.0
2019-08-28T11:38:06.577Z
While there are certainly some risks to manage when holding that much bitcoin, a reorg is not one of them.
hedgedandlevered
CC BY-SA 4.0
2019-08-27T23:49:14.337Z
2019-08-27T23:49:14.337Z
hedgedandlevered
<p>if a block takes 10 minutes to be mined</p>

<p>does it need 21 minutes to be reorged?</p>

<p>if the reorg started immediately after the block was mined</p>

<p>because 100% was mining and 51.5% will reorg</p>

<p>how long does it take to reorg 5000 block ? 70 days?</p>

<p>is 70 days of reorging a huge thing that would make the people stop believing in BTC ?</p>

<p>all of my questions and availability here is because i am selling my business for 5300 BTC and i dont need to be F&amp;&amp;&amp;ed with reorging later if i will not use them</p>

<p>this was also my point in the last questions for creating custom wallet offline</p>

CC BY-SA 4.0
2019-08-27T13:41:41.483Z
what is mean "reorged"? in this context?
vincenzopalazzo
CC BY-SA 4.0
2019-08-27T13:50:20.840Z
refunding the sent transactions with huge reversal mining power
BTC involver
CC BY-SA 4.0
2019-08-27T14:00:23.437Z
mh with on bitcoin exist the reorged action?
vincenzopalazzo
CC BY-SA 4.0
2019-08-27T14:01:46.150Z
yes but you need much money to reorg
BTC involver
CC BY-SA 4.0
2019-08-27T21:28:16.027Z
Possible duplicate of [Why is 6 the number of confirms that is considered secure?](https://bitcoin.stackexchange.com/questions/1170/why-is-6-the-number-of-confirms-that-is-considered-secure)
chytrik
<chain-reorganization>
bitcoin reorg question
BTC involver
# bitcoin reorg question

(Asked by: username_0 on 2019-08-27)

if a block takes 10 minutes to be mined

does it need 21 minutes to be reorged?

if the reorg started immediately after the block was mined

because 100% was mining and 51.5% will reorg

how long does it take to reorg 5000 block ? 70 days?

is 70 days of reorging a huge thing that would make the people stop believing in BTC ?

all of my questions and availability here is because i am selling my business for 5300 BTC and i dont need to be F&&&ed with reorging later if i will not use them

this was also my point in the last questions for creating custom wallet offline

**Tags:** chain-reorganization

> **Comments:**
> **username_1**: what is mean "reorged"? in this context?  
> **username_0**: refunding the sent transactions with huge reversal mining power  
> **username_1**: mh with on bitcoin exist the reorged action?  
> **username_0**: yes but you need much money to reorg  
> **username_2**: Possible duplicate of [Why is 6 the number of confirms that is considered secure?](https://bitcoin.stackexchange.com/questions/1170/why-is-6-the-number-of-confirms-that-is-considered-secure)  

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## 1 answers

### Answer by username_3 on 2019-08-27. Score: 0 | Accepted answer

First you need to define "reorg". Under the definition I'll use, the minimum reorg is two blocks. The definition would be:
"A reorginization occurs when a block is broadcast with a history that is incompatible with the previously work-heaviest\*\* known blockchain, under the same consensus rules"

Say a block is mined onto the height 593000 block, with hash `000000000000000000a11...` so that apparently, block 593001 has been found, and many miners are now mining based off of this hash.

Now imagine that someone broadcasts block 593002 with hash `000000000000000000c84...`but upon examining block 593001, you see that the hash is `000000000000000000b5c...`

A reorg has just taken place. Someone mined block 593001, and without broadcasting it (or perhaps after broadcasting it too late), mined 593002 on top of it. Now any transactions in the block with hash `000000000000000000a11...` have not been confirmed (one of which was the original miner sending the block reward transaction to themselves), since the (valid) block that contains them has been orphaned.

As far as "how long", a reorg is relative to the observer, so one could technically take place before you observe the original chain at all.

\*\* *essentially, the longest chain, but there are exceptions where a "reorg" could be a shorter chain in terms of number of blocks, when a shorter chain contains "more" proof of work. This is outside the scope of this answer.*

> **Comments:**
> **username_0**: so lets assume they want to reorg a 5,300 BTC transaction after 30 days of its creation what is the situation ? if around 100 blocks daily is trying to reorg after 3000 blocks, and here am talking about huge reorging power. i just need to know when there are no chance for reorging to i can gave up the company to them after this time frame from their transaction.  
> **username_3**: The size of the transaction is completely irrelevant. Realistically, waiting for just 1 confirmation will give you an extremely high chance of your transaction being permanent, especially in the absence of double spend attempts, which are trivial to detect. (I am ONLY referring to the Bitcoin blockchain here. All other blockchains have significantly weaker security. This is the advantage of using Bitcoin vs any altcoins) For sending bitcoin, 2 confirmations is overkill for any realistic scenario.  
> **username_0**: its not irrelevant because if its low the miners wont accept to help them reorging but with a huge reword they would accept, so if they risk 2650 btc as fees to the miners to get net of 2650 btc back? that's my point.  
> **username_3**: No. First, you'd need over 51% of the hashing power to collude to do this, which is essentially impossible to coordinate at all, even if you could convince them. Second, you'd need to convince them to basically break Bitcoin, after they have spent millions of dollars buying specialized equipment that is useless without Bitcoin. And all of this without your counterparty suspecting anything, all for what is essentially still a relatively small tx vs miner rewards (1800 btc are mined daily). It's just not something that would be in anyone's financial interest that had mining machines.  
> **username_3**: and then on top of that, you've only saved yourself bitcoin, which is now nearly worthless in traditional currency terms due to the 51% attack. So you don't even have upside in this ridiculous scenario.  
> **username_0**: do you mean that i should giveup taking it as btc ?  
> **username_3**: could you elaborate? Taking what? Against what alternative?  
> **username_0**: 55,000,000 USD or 5,300 BTC. in both cases i will not use the money for years.  
> **username_3**: While there are certainly some risks to manage when holding that much bitcoin, a reorg is not one of them.  

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