The general consensus in the Bitcoin network is to wait for 6 confirmations or 1 hour on a transaction before it can be considered completely irreversible. However, when it comes to altcoins that use different block generation rate, some people go with ~6 confirmations, while others use ~1 hour worth of blocks as the standard confirmation model.

I am wondering if there is any consensus on which approach is more proper? Assuming the altcoin network in question is under no threat of a 51% attack, should companies under a risk of theft attempts (say, exchanges) wait for about 6 confirmations regardless of the block generation rate, about 1 hour worth of confirmations also disregarding the generation rate, or for the higher of 6 of 1 hour worth of confirmations if blocks are generated slower than 1 block per 10 minutes?


2 Answers 2


See https://bitcoil.co.il/Doublespend.pdf. What matters is the number of blocks, not time elapsed or average time for this many blocks.

Also, the idea of "wait for 6 confirmations or 1 hour" in Bitcoin is a myth. If 1 hour passes with 3 confirmations you're less secure than if 30 minutes passed with 3 confirmations, because the attacker would have had more time to build his competing branch.

  • Would this be true even if the block size were much larger and confirmation times were much shorter, such that the time to propagate a block to the majority of the network constituted a large portion of the confirmation time?
    – tlrobinson
    Commented Feb 19, 2014 at 9:16

If you look at the bitcoin protocol specification the calculation of 6 confirmations are considered very unlikely to reverse (even with over 51% of the network hash power) In the case of bitcoin (10 min blocks) 6 confirmations is one hour, with QRK for example (30 sec blocks) its 3 min, if you wait one hour you get to 120 confirmations.

To answer the question we should also add the difficulty factor which will reflect the processing power put in to the mining process, the more processing effort put in to mining by the network the more processing power a single attacker will need to be able to get to 51% if the difficulty is high one could assume less confirmations are safer.

But that's just my opinion based on my current understanding.

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