On Fri, Sep 23, 2016 at 09:57:01AM +0000, Luke Dashjr via bitcoin-dev wrote:
> This BIP describes a new opcode (OP_CHECKBLOCKATHEIGHT) for the Bitcoin 
> scripting system to address reissuing bitcoin transactions when the coins they 
> spend have been conflicted/double-spent.
> 
> https://github.com/luke-jr/bips/blob/bip-cbah/bip-cbah.mediawiki
> 
> Does this seem like a good idea/approach?

Your BIP is a bit confusing: you say "In some circumstances, users may wish to
spend received bitcoins before they have confirmed on the blockchain", but what
you're really referring to isn't spending unconfirmed outputs - which
OP_CHECKBLOCKATHEIGHT can't protect - but rather spending outputs with a small
number of confirmations.

In the existing ecosystem, if multi-block reorgs were a regular event Bitcoin
would be in a lot of trouble; since they're rare, advising wallet authors to
simply refuse to make transactions for some time after such a reorg may be a
better solution. After all, a multi-block reorg is a strong indication that
there's somehting very wrong with the network, and it'd be safer to stop using
Bitcoin for awhile until things settle down.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org