[comboy]

Transactions follow very specific binary format. I don't think it's even plausible that you could find collision within those constraints. Plus, as you said it is double hashed. So then you would have to find collision within small fixed amount 32 bytes. It's just not happening.

Regarding the second one, google bitcoin address collision, it was repeated so many times with great analogies that I'm not going to try to do it here yet another time.

[garmaine]

The post I was responding to was the exact hypothetical “if SHA-2 were broken...”

All arguments about collision and preimage resistance are based on the assumption of SHA-2 doing what we think it does. A catastrophic break of SHA-2 would destroy the bitcoin ledger.