BIP 0147 - Dealing with dummy stack element malleability (soft fork)

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Data sheet for Dealing with dummy stack element malleability

Title	Dealing with dummy stack element malleability
Layer	Consensus (soft fork)
Author	Johnson Lau
Comments-Summary	No comments yet.
Comments-URI	https://github.com/bitcoin/bips/wiki/Comments:BIP-0147
Status	Final
Type	Standards Track
Created	2016-09-02
Post History
Description	https://github.com/bitcoin/bips/blob/master/bip-0147.mediawiki
License	PD

Note: The following is an excerpt from the official 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 specifies proposed changes to the Bitcoin transaction validity rules to fix a malleability vector in the extra stack element consumed by OP_CHECKMULTISIG and OP_CHECKMULTISIGVERIFY.

Motivation

Signature malleability refers to the ability of any relay node on the network to transform the signature in transactions, with no access to the relevant private keys required. For non-segregated witness transactions, signature malleability will change the txid and invalidate any unconfirmed child transactions. Although the txid of segregated witness ( BIP141) transactions is not third party malleable, this malleability vector will change the wtxid and may reduce the efficiency of compact block relay ( BIP152).A design flaw in OP_CHECKMULTISIG and OP_CHECKMULTISIGVERIFY causes them to consume an extra stack element (“dummy element”) after signature validation. The dummy element is not inspected in any manner, and could be replaced by any value without invalidating the script. This document specifies a new rule to fix this signature malleability.