From: "Luke-Jr" <luke@dashjr.org>
To: bitcoin-development@lists.sourceforge.net
Date: Sun, 3 Nov 2013 00:33:55 +0000
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Message-Id: <201311030033.56983.luke@dashjr.org>
Subject: Re: [Bitcoin-development] Message Signing based authentication
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On Sunday, November 03, 2013 12:29:28 AM Allen Piscitello wrote:
> This was one of my concerns when implementing a scheme where you sign a
> refund transaction before the original transaction is broadcast.  I
> originally tried to pass a hash and have the server sign it.  However, I
> had no way to know that what I was signing wasn't a transaction that was
> spending my coins!  So I changed the code to require sending the full
> transaction, not just the hash.  The other way to mitigate this is through
> not having any unspent outputs from this key.

Well, there's no use case to sign with an address that has already been sent 
coins. The main problem with enforcing this is that you can't exactly stop 
someone from sending to an "identity" address.

Luke