On Thu, Nov 17, 2016 at 12:43 AM, Eric Voskuil <eric@voskuil.org> wrote:

> This means that all future transactions will have different txids...
rules do guarantee it.

No, it means that the chance is small, there is a difference.

I think we are mostly in agreement then? It is just terminology.

In terms of discussing the BIP, barring a hash collision, it does make duplicate txids impossible.

Given that a hash collision is so unlikely, the qualifier should be added to those making claims that require hash collisions rather than those who assume that they aren't possible.

You could have said "However nothing precludes different txs from having the same hash, but it requires a hash collision".

Thinking about it, a re-org to before the enforcement height could allow it. The checkpoints protect against that though.

As such this is not something that a node
can just dismiss.

The security of many parts of the system is based on hash collisions not being possible.