OP_RETURN limit is 80 bytes (83 bytes if you include the overhead). But the limitation only applies during relaying transaction. Pool/miner could create coinbase transaction or include their own transaction with OP_RETURN with far bigger size, which means it can be used for more complex advertising/labeling.
was it not reduced to 40 bytes, or was that in a dream?
surely it wasn't reduced to 40, then subsequently bumped back up to 80 again?The first is that the manufacturer will not mind that his label is put even untruthfully. It is for advertising purposes.
It is the same kind of proof like with Casascius coins: the private key is protected from viewing by anyone and if you want to sell that mining device to someone else, that person will be able to tell if that private key is still inside or was it revealed by scraping something, detaching some factory labels that has "warranty void if removed" or similar signs, etc.
Also, mining device don't have to lock coins on manufacturer's key, all that is needed is signing blocks with that key
Also, mining device don't have to lock coins on manufacturer's key, all that is needed is signing blocks with that key
no, and no
you're conceding already that the manufacturer or the miner can falsify the information (or sell the public key in a block signing scheme): trust required
cryptography can secure data
cryptography cannot secure real physical objects in the real world
no amount of extra cryptography can solve this problem