[Bitcoin-development] [BIP] Normalized Transaction IDs

Christian Decker decker.christian at gmail.com
Tue May 19 10:43:39 UTC 2015

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

> On Tue, May 19, 2015 at 9:28 AM, Christian Decker <
> decker.christian at 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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