On Tue, May 19, 2015 at 11:16 AM Tier Nolan <tier.nolan@gmail.com> wrote:

On Tue, May 19, 2015 at 9:28 AM, Christian Decker <decker.christian@gmail.com> wrote:
Thanks Stephen, I hadn't thought about BIP 34 and we need to address this in both proposals. If we can avoid it I'd like not to have one transaction hashed one way and other transactions in another way.

The normalized TXID cannot depend on height for other transactions. Otherwise, it gets mutated when been added to the chain, depending on height.

Well in the case of coinbase transactions we want them to be dependent on the height they are included in, which is not a problem since they are only valid in conjunction with the block that mined them.

An option would be that the height is included in the scriptSig for all transactions, but for non-coinbase transctions, the height used is zero.

No need to add an extra field to the transaction just to include the height. We can just add a rule that the height specified in the scriptSig in coinbase transactions (and only coinbase transactions) is copied into the locktime of the transaction before computing the normalized transaction ID and leave the locktime untouched for all normal transactions

I think if height has to be an input into the normalized txid function, the specifics of inclusion don't matter.

The previous txid for coinbases are required to be all zeros, so the normalized txid could be to add the height to the txids of all inputs. Again, non-coinbase transactions would have heights of zero.

Is there a specific reason why that was not chosen at the time?

I assumed that since the scriptSig in the coinbase is specifically intended to be "random" bytes/extra nonce, so putting a restriction on it was guaranteed to be backward compatible.

Sounds reasonable :-)

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