==== BIP 0030 - Duplicate transactions (soft fork)  ====
[[dido:public:ra:xapend:xapend.b_stds:defact:bitcoin:bips| return to the Bitcoin Improvement Proposals ]]

<table>
<caption>Data sheet for Duplicate transactions  </caption>
| Title                      | Duplicate transactions  |
| Layer                      | Consensus (soft fork) |
| Author                     | Pieter Wuille	 |
| Comments-Summary           | No comments yet. |
| Comments-URI               | [[https://github.com/bitcoin/bips/wiki/Comments:BIP-0030]]    |
| Status                      | Final | 
| Type                       | Standards Track | 
| Created                    | 2012-02-22  |
| Post History               |  |
| Description                | [[https://github.com/bitcoin/bips/blob/master/bip-0030.mediawiki]] |
| License                    | BSD-2-Clause |
</table>

  : **Note**: The following is an excerpt from the official [[dido:public:ra:xapend:xapend.a_glossary:b:bitcoin|Bitcoin]] site. It is provided here as a convenience and is not authoritative. Refer to the original document(s) as the authoritative reference.

=== Abstract ===
  : //This document gives a specification for dealing with duplicate transactions in the block chain, in an attempt to solve certain problems the reference implementation has with them.//

=== Copyright ===
  : //This BIP is licensed under the 2-clause BSD license.//

=== Motivation ===
  ://So far, the Bitcoin reference implementation always assumed duplicate transactions (transactions with the same [[dido:public:ra:xapend:xapend.a_glossary:i:id|identifier]]) didn't exist. This is not true; in particular coinbases are easy to duplicate, and by building on duplicate coinbases, duplicate normal transactions are possible as well. Recently, an attack that exploits the reference implementation's dealing with duplicate transactions was described and demonstrated. It allows reverting fully-confirmed transactions to a single [[dido:public:ra:xapend:xapend.a_glossary:c:confirmation|confirmation]], making them vulnerable to become unspendable entirely. Another attack is possible that allows forking the block chain for a subset of the network.//