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From: Joel Joonatan Kaartinen <joel.kaartinen@gmail.com>
To: roconnor@theorem.ca
Cc: bitcoin-development@lists.sourceforge.net
Subject: Re: [Bitcoin-development] Alternative to OP_EVAL
Date: Sat, 31 Dec 2011 11:54:13 +0200	[thread overview]
Message-ID: <1325325253.2800.3.camel@mei> (raw)
In-Reply-To: <alpine.LRH.2.00.1112291135040.22327@theorem.ca>

Wouldn't it work to restrict the number of executions of OP_EVAL allowed
per transaction? That way it wouldn't allow for unlimited looping. If
there's too many OP_EVAL executions during the transaction evaluation,
just consider the transaction illegal. 3 would be enough for the
purposes people have been planning for here I think.

- Joel

On Thu, 2011-12-29 at 11:42 -0500, roconnor@theorem.ca wrote:
> On Thu, 29 Dec 2011, theymos wrote:
> 
> > On Thu, Dec 29, 2011, at 01:55 AM, roconnor@theorem.ca wrote:
> >> The number of operations executed is still bounded by the number of
> >> operations occurring in the script.  With the OP_EVAL proposal the
> >> script language becomes essentially Turing complete, with only an
> >> artificial limit on recursion depth preventing arbitrary computation
> >> and there is no way to know what code will run without executing it.
> >
> > Even if OP_EVAL allowed infinite depth, you'd still need to explicitly
> > specify all operations performed, since there is no way of looping.
> 
> That's not true.  Gavin himself showed how to use OP_EVAL to loop:
> OP_PUSHDATA {OP_DUP OP_EVAL} OP_DUP OP_EVAL.
> 
> Basically OP_DUP lets you duplicate the code on the stack and that is the 
> key to looping.  I'm pretty sure from here we get get Turing completeness. 
> Using the stack operations I expect you can implement the SK-calculus 
> given an OP_EVAL that allows arbitrary depth.
> 
> OP_EVAL adds dangerously expressive power to the scripting language.
> 





  parent reply	other threads:[~2011-12-31  9:54 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-29  6:55 [Bitcoin-development] Alternative to OP_EVAL roconnor
2011-12-29  8:44 ` theymos
2011-12-29 16:42   ` roconnor
2011-12-30 12:01     ` Chris Double
2011-12-30 17:19       ` roconnor
2012-01-02 15:14         ` Stefan Thomas
2012-01-02 15:59           ` Gavin Andresen
2012-01-02 16:42             ` roconnor
2012-01-02 17:10             ` Stefan Thomas
2011-12-31  9:54     ` Joel Joonatan Kaartinen [this message]
2011-12-31 17:28       ` Zell Faze
2011-12-29 16:23 ` Gavin Andresen
2011-12-29 17:01   ` roconnor
2011-12-29 17:06     ` Luke-Jr
2011-12-29 18:00     ` Gavin Andresen
2011-12-29 19:54       ` Stefan Thomas
2011-12-29 19:08 ` Pieter Wuille
2011-12-29 21:00   ` Pieter Wuille
2011-12-29 21:31   ` Alan Reiner

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