Subject: [Bitcoin-development] BIP16/17 replacement

From: Andy Parkins <[email-masked]>
Date: Tue, 31 Jan 2012 16:50:58 +0000

Hello,

Gulp.  Am a little nervous about wading into this swamp.  However, it seems 
to me that the debate has veered into the personal and away from the 
technical.  Surely if there are objections to both suggestions, that another 
solution might be better?  The answer doesn't have to be A or B, if the 
answer C turns out to be acceptable.

That being said; I am not confident enough to start making BIPs so I offer 
this idea up for my traditional mailing-list roasting but with the hope that 
I blindly stumble toward something more acceptable to everyone.

----

If the change is going to be a big one anyway and will require a client 
upgrade why not...

 - Increase the version number in transactions to make a new transaction
   structure
 - Dump the "scriptPubKey" field completely.  Everything will be pay-to-
   script-hash in version2 transactions
 - Replace it with "hashOfClaimingScript"
 - Add an "unsignedParameters" array.

hashOfClaimingScript is _not_ script.  It's just the hash of the script that 
is allowed to claim the output.  Then before scriptSig is allowed to run, it 
is hashed and compared against the hashOfClaimingScript.

unsignedParameters replaces the need for all the crazy messing around that 
OP_CHECKSIG currently does because it is specifically a block of the 
transaction that it not signed (although I would include the array size bytes 
in the signature calculation), therefore no script filtering is necessary.

The claiming script, scriptSig, can then be checked against whatever list of 
templates you like.  For pay-to-address it will probably look like:

  OP_PUSHPARAMETER {0}
  OP_PUSH { <claimant public key> }
  OP_CHECKSIGVERIFY

Handling the more complicated transactions (they're the point of all this 
after all) is pretty obvious; the unsignedParameters block can hold as many 
signatures as you like.  It also removes the need for OP_CHECKMULTISIG, since 
the script can specify the signature conditions.  e.g. a 2-of-3 script:

  OP_PUSHPARMETER {0}
  OP_PUSH { <claimant public key0> }
  OP_CHECKSIG
  OP_PUSHPARMETER {1}
  OP_PUSH { <claimant public key1> }
  OP_CHECKSIG
  OP_PUSHPARMETER {1}
  OP_PUSH { <claimant public key1> }
  OP_CHECKSIG
  OP_ADD
  OP_ADD
  OP_PUSH {1}
  OP_GREATERTHAN

(I'm sure someone cleverer than I can improve on the above)

-----

Let the flaming commence...

Andy

-- 
Dr Andy Parkins
[email-masked]