[Bitcoin-development] Double-spending unconfirmed transactions is a lot easier than most people realise

Mark Friedenbach mark at monetize.io
Wed Apr 23 06:35:06 UTC 2014

On 04/22/2014 09:29 PM, Jan Møller wrote:
>>Of course, this is an especially difficult case, as you must send the
>>double-spend after the original transaction - normally just sending a
>>non-standard tx to Eligius first would suffice. Note how this defeats
>>Andresen's double-spend-relay patch(3) as proposed since the
>>double-spend is a non-standard transaction.
> Why can't you send a non-standard tx to Eligius first in this scenario?​
> Is it because LuckyBit is connected directly to Eligius, and does
> Eligius relay (not only mine) non-standard transactions?

Because you only want to double-spend if you loss the bet. If you tried
to double-spend every bet, there'd be no point :)

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