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From: Luke Dashjr <luke@dashjr.org>
To: bitcoin-dev@lists.linuxfoundation.org,
 Peter Todd <pete@petertodd.org>
Date: Wed, 20 Jul 2016 06:17:39 +0000
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Subject: Re: [bitcoin-dev] BIP draft: HTLC transactions
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On Wednesday, July 20, 2016 5:46:54 AM Peter Todd via bitcoin-dev wrote:
> On Tue, Jul 19, 2016 at 10:35:39PM -0600, Sean Bowe via bitcoin-dev wrote:
> > I'm requesting feedback for Hash Time-Locked Contract (HTLC) transactions
> > in Bitcoin.
> > 
> > HTLC transactions allow you to pay for the preimage of a hash. CSV/CLTV
> > can be used to recover your funds if the other party is not cooperative.
> > These
> > 
> > scripts take the following general form:
> >     [HASHOP] <digest> OP_EQUAL
> >     OP_IF
> >     
> >         <seller pubkey>
> >     
> >     OP_ELSE
> >     
> >         <num> [TIMEOUTOP] OP_DROP <buyer pubkey>
> >     
> >     OP_ENDIF
> >     OP_CHECKSIG
> 
> Note that because you're hashing the top item on the stack regardless
> scriptSig's that satisfy HTLC's are malleable: that top stack item can be
> changed anything in the digest-not-provided case and the script still
> passes.

OP_SIZE
OP_IF
  [HASHOP] <digest> OP_EQUALVERIFY
  <seller pubkey>
OP_ELSE
  <num> [TIMEOUTOP]
  <buyer pubkey>
OP_ENDIF
OP_CHECKSIG