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From: Tony Churyumoff <tony991@gmail.com>
Date: Wed, 10 Aug 2016 10:53:01 +0300
Message-ID: <CAL3p6zrYwxFRC5JctwKsLwEzENWL0B2iUgO3crubaYkc=m5SdQ@mail.gmail.com>
To: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: [bitcoin-dev] Fwd: Hiding entire content of on-chain transactions
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This troll is harmless.  A duplicate spend proof should also be signed
by the same user (Alice, in your example) to be considered a double
spend.

2016-08-09 3:18 GMT+03:00 James MacWhyte <macwhyte@gmail.com>:
> One more thought about why verification by miners may be needed.
>
> Let's say Alice sends Bob a transaction, generating output C.
>
> A troll, named Timothy, broadcasts a transaction with a random hash,
> referencing C's output as its spend proof. The miners can't tell if it's
> valid or not, and so they include the transaction in a block. Now Bob's
> money is useless, because everyone can see the spend proof referenced and
> thinks it has already been spent, even though the transaction that claims it
> isn't valid.
>
> Did I miss something that protects against this?
>