Reuse of pub key hashes in coinbase outputs

[No_2]

I remember reading somewhere that at a certain block depth the network began enforcing that coinbase output addresses could not re-used because this was causing problems. Something to do with referencing the second coinbase with the same pub key hash, meaning the bitcoins in this second coinbase effectively became undependable.

Sorry to be so vague but is this correct and if so why? If not is it closely related to a similar constraint for coinbase outputs?

[achow101]

No... Where did you hear that? There is nothing special about a coinbase output. It is still spent from in the same way.

[Foxpup]

No... Where did you hear that? There is nothing special about a coinbase output. It is still spent from in the same way.

Actually, there's something very special about coinbase transactions: it's possible for two of them to be identical, if they have the same outputs. Normal transactions cannot possibly be identical as they must spend different inputs, but coinbase transactions have no inputs to distinguish them. Identical coinbase transactions are problematic because only one copy of the transaction can be spent; all others simply destroy the coins. Miners have indeed accidentally lost money this way. OP is asking about the soft-fork to make blocks with identical coinbases invalid, which I don't recall the details of.

[achow101]

No... Where did you hear that? There is nothing special about a coinbase output. It is still spent from in the same way.

Actually, there's something very special about coinbase transactions: it's possible for two of them to be identical, if they have the same outputs. Normal transactions cannot possibly be identical as they must spend different inputs, but coinbase transactions have no inputs to distinguish them. Identical coinbase transactions are problematic because only one copy of the transaction can be spent; all others simply destroy the coins. Miners have indeed accidentally lost money this way. OP is asking about the soft-fork to make blocks with identical coinbases invalid, which I don't recall the details of.

But that's irrelevant now due to requiring the block height in the coinbase, which will thus make coinbase transactions unique. BIP 34: https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki

[Foxpup]

But that's irrelevant now due to requiring the block height in the coinbase, which will thus make coinbase transactions unique. BIP 34: https://github.com/bitcoin/bips/blob/master/bip-0034.mediawiki

Yes, that must be what I was thinking of. (It seems I recall fewer details of it than I thought I did.)

[No_2]

Thanks, so have we hit the 75% threshold now as per BIP 34? I.e. are all blocks now numbered removing the ambiguity about referencing the coinbase if it uses a duplicate pub key hash in its output?

EDIT: Ah, yes. Missed it at the bottom of the BIP 34 description: "Block number 227,835 (timestamp 2013-03-24 15:49:13 GMT) was the last version 1 block."