I understand that using the current block hash gives the miner the ability to possibly discard the block, but my question is about using a block hash from a past block. For example, I could look 128 blocks in the past and use that hash. The miner would be all but guaranteed to mine an orphan if they attempt to mine on top of block-129 and whatever block hash they come up with for the current block has no bearing on the outcome. Specifically, they and a cartel of miners would need to censor the transaction and any block that contained it, wouldn't they?

What are some reasons this would not be a good idea for something like a high stakes lottery?

1 Answer 1


In general the concept of randomness depends on what we need. In your case a random value is not meant to be only random but also unpredictable. A past hash value is not unpredictable.

If you use a past hash as a seed for your randomness anyone can calculate the resulting random value in advance as everyone knows the past hash. This information can often be abused - for example they only participate in the lottery when they know the used random value will be in their favour.

  • Thanks - I wasn't thinking clearly.
    – Kyle Bahr
    Commented Jan 4, 2020 at 6:04

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