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


1 Answer 1


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.

  • 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. Commented Aug 28, 2019 at 1:19
  • 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. Commented Aug 28, 2019 at 1:30
  • 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. Commented Aug 28, 2019 at 1:33
  • 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. Commented Aug 28, 2019 at 2:15
  • 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. Commented Aug 28, 2019 at 2:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.