BIP: 147 Layer: Consensus (soft fork) Title: Dealing with dummy stack element malleability Author: Johnson Lau <firstname.lastname@example.org> 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 License: PD
This document specifies proposed changes to the Bitcoin transaction
validity rules to fix a malleability vector in the extra stack element
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
invalidate any unconfirmed child transactions. Although the
transactions is not third party malleable, this malleability vector will
wtxid and may reduce the efficiency of compact block relay
A design flaw in
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.
To fix the dummy element malleability, a new consensus rule
NULLDUMMY") is deployed to require that the dummy element MUST be
the empty byte array. Anything else makes the script evaluate to false
NULLDUMMY rule applies to
OP_CHECKMULTISIGVERIFY in pre-segregated scripts, and also
pay-to-witness-script-hash scripts described in BIP141.
This BIP will be deployed by "version bits" BIP9 using the same parameters for BIP141 and BIP143, with the name "segwit" and using bit 1.
For Bitcoin mainnet, the BIP9 starttime is midnight 15 November 2016 UTC (Epoch timestamp 1479168000) and BIP9 timeout is midnight 15 November 2017 UTC (Epoch timestamp 1510704000).
For Bitcoin testnet, the BIP9 starttime is midnight 1 May 2016 UTC (Epoch timestamp 1462060800) and BIP9 timeout is midnight 1 May 2017 UTC (Epoch timestamp 1493596800).
The reference client has produced compatible signatures from the
beginning, and the
NULLDUMMY rule has been enforced as relay policy by
the reference client since v0.10.0. There has been no transactions
violating the requirement being added to the chain since at least August
For all scriptPubKey types in actual use, non-compliant signatures can trivially be converted into compliant ones, so there is no loss of functionality by this requirement. Users MUST pay extra attention to this new rule when designing exotic scripts.
An implementation for the reference client is available at https://github.com/bitcoin/bitcoin/pull/8636
Peter Todd is the original author of NULLDUMMY. This document is extracted from the previous BIP62 proposal, which was composed by Pieter Wuille and had input from various people.
This document is placed in the public domain.