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From: Rusty Russell <rusty@rustcorp.com.au>
To: Luke Dashjr <luke@dashjr.org>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Date: Sat, 01 Oct 2016 13:31:04 +0930
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Subject: Re: [bitcoin-dev] BIP draft: OP_CHECKBLOCKATHEIGHT
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Luke Dashjr via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> writes:

> 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?

Prefer a three-arg version (gbits-to-compare, blocknum, hash):
- If <bits> is 0 or > 256, invalid.
- If the hash length is not (<bits> + 7) / 8, invalid.
- If the hash unused bits are not 0, invalid.
- Otherwise <bits> of hash is compared to lower <bits> of blockhash.

This version also lets you play gambling games on-chain!

Or maybe I've just put another nail in CBAH's coffin?

Cheers,
Rusty.