[Bitcoin-development] Duplicate transactions vulnerability

Pieter Wuille pieter.wuille at gmail.com
Tue Feb 28 16:48:39 UTC 2012

Hello all,

as some of you may know, a vulnerability has been found in how the
Bitcoin reference client deals with duplicate transactions. Exploiting
it is rather complex, requires some hash power, and has no financial
benefit for the attacker. Still, it's a security hole, and we'd like
to fix this as soon as possible.

A simple way to fix this, is adding an extra protocol rule[1]:

  Do not allow blocks to contain a transaction whose hash is equal to
that of a former transaction which has not yet been completely spent.

I've written about it in BIP30[2]. There is a patch for the reference
client, which has been tested and verified to make the attack
impossible. The change is backward compatible in the same way BIP16
is: if a supermajority of mining power implements it, old clients can
continue to function without risk.

The purpose of this mail is asking for support for adding this rule to
the protocol rules. If there is consensus this rule is the solution, I
hope pools and miners can agree to update their nodes without lengthy
coinbase-flagging procedure that would only delay a solution. So, who
is in favor?

  [1] https://en.bitcoin.it/wiki/Protocol_rules
  [2] https://en.bitcoin.it/wiki/BIP_0030


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