[Lightning-dev] Anchor transaction for no expiration channels without segwit

[Tier Nolan]

On Tue, Feb 7, 2017 at 2:39 AM, Nicolas Dorier <nicolas.dorier at gmail.com>
wrote:

> Good point, actually, a simpler way to do it, is for TX2 to be nTimelocked
> after bounty's expiration.
>

That works too and keeps the transaction smaller.

I think a symmetrically funded channel needs 4 1BTC outputs, so it is
pretty much two single funded channels.  It would be slightly smaller than
2 transactions to open the channel.

TX1

Input
2 from Alice
2 from Bob

Output
1:  (Alice + Bob) OR (Bob + AliceSecret)
1:  (Alice + Bob) OR (Alice + BobSecret)
1:  (Bob + timeout(now + T)) OR (Alice + AliceSecret)
1:  (Alice + timeout(now + T)) OR (Bob + BobSecret)

TX2
locktime:  now + 2T

Input
TX1/0: signed by (Alice + Bob)
TX1/1: signed by (Alice + Bob)
Output
Initial channel paying Alice & Bob 1BTC each

---------------------------------------

Alice and Bob create TX1, sign it and share the result.

Alice and Bob create TX2, sign it and share the result.

Abort for those 2 steps:
*  If one signs and the other doesn't then the signer should spend their
inputs to be safe.
*  If TX1 is broadcast, then they can both spend their timeouts to recover
their funds, so it is safe.

Once they both have signed versions of TX1 and TX2, they should broadcast
TX1.  This initializes the channel.

If TX1 is mutated, then they should both abort and spend their timeouts and
recover their funds.
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