mirror of
https://github.com/bitcoin/bips.git
synced 2024-11-19 01:40:05 +01:00
959fecc15b
- Update all Accepted status to Proposed (renamed status) - The BIP Comments preamble headers added to every BIP - The License preamble headers have been added to all BIPs with a Copyright section
127 lines
4.7 KiB
Plaintext
127 lines
4.7 KiB
Plaintext
<pre>
|
|
BIP: 113
|
|
Layer: Consensus (soft fork)
|
|
Title: Median time-past as endpoint for lock-time calculations
|
|
Author: Thomas Kerin <me@thomaskerin.io>
|
|
Mark Friedenbach <mark@friedenbach.org>
|
|
Comments-Summary: No comments yet.
|
|
Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0113
|
|
Status: Final
|
|
Type: Standards Track
|
|
Created: 2015-08-10
|
|
License: PD
|
|
</pre>
|
|
|
|
|
|
==Abstract==
|
|
|
|
This BIP is a proposal to redefine the semantics used in determining a
|
|
time-locked transaction's eligibility for inclusion in a block. The
|
|
median of the last 11 blocks is used instead of the block's timestamp,
|
|
ensuring that it increases monotonically with each block.
|
|
|
|
|
|
==Motivation==
|
|
|
|
At present, transactions are excluded from inclusion in a block if the
|
|
present time or block height is less than or equal to that specified
|
|
in the locktime. Since the consensus rules do not mandate strict
|
|
ordering of block timestamps, this has the unfortunate outcome of
|
|
creating a perverse incentive for miners to lie about the time of
|
|
their blocks in order to collect more fees by including transactions
|
|
that by wall clock determination have not yet matured.
|
|
|
|
This BIP proposes comparing the locktime against the median of the
|
|
past 11 block's timestamps, rather than the timestamp of the block
|
|
including the transaction. Existing consensus rules guarantee this
|
|
value to monotonically advance, thereby removing the capability for
|
|
miners to claim more transaction fees by lying about the timestamps of
|
|
their block.
|
|
|
|
This proposal seeks to ensure reliable behaviour in locktime calculations
|
|
as required by BIP65 (CHECKLOCKTIMEVERIFY) and matching the behavior of
|
|
BIP68 (sequence numbers) and BIP112 (CHECKSEQUENCEVERIFY).
|
|
|
|
|
|
==Specification==
|
|
|
|
The values for transaction locktime remain unchanged. The difference is only in
|
|
the calculation determining whether a transaction can be included. Instead of
|
|
an unreliable timestamp, the following function is used to determine the current
|
|
block time for the purpose of checking lock-time constraints:
|
|
|
|
enum { nMedianTimeSpan=11 };
|
|
|
|
int64_t GetMedianTimePast(const CBlockIndex* pindex)
|
|
{
|
|
int64_t pmedian[nMedianTimeSpan];
|
|
int64_t* pbegin = &pmedian[nMedianTimeSpan];
|
|
int64_t* pend = &pmedian[nMedianTimeSpan];
|
|
for (int i = 0; i < nMedianTimeSpan && pindex; i++, pindex = pindex->pprev)
|
|
*(--pbegin) = pindex->GetBlockTime();
|
|
std::sort(pbegin, pend);
|
|
return pbegin[(pend - pbegin)/2];
|
|
}
|
|
|
|
Lock-time constraints are checked by the consensus method IsFinalTx().
|
|
This method takes the block time as one parameter. This BIP proposes
|
|
that after activation calls to IsFinalTx() within consensus code use
|
|
the return value of `GetMedianTimePast(pindexPrev)` instead.
|
|
|
|
The new rule applies to all transactions, including the coinbase transaction.
|
|
|
|
A reference implementation of this proposal is provided by the
|
|
following pull request:
|
|
|
|
https://github.com/bitcoin/bitcoin/pull/6566
|
|
|
|
|
|
==Deployment==
|
|
|
|
This BIP is to be deployed by "versionbits" BIP9 using bit 0.
|
|
|
|
For Bitcoin '''mainnet''', the BIP9 '''starttime''' will be midnight 1st May 2016 UTC (Epoch timestamp 1462060800) and BIP9 '''timeout''' will be midnight 1st May 2017 UTC (Epoch timestamp 1493596800).
|
|
|
|
For Bitcoin '''testnet''', the BIP9 '''starttime''' will be midnight 1st March 2016 UTC (Epoch timestamp 1456790400) and BIP9 '''timeout''' will be midnight 1st May 2017 UTC (Epoch timestamp 1493596800).
|
|
|
|
This BIP must be deployed simultaneously with BIP68 and BIP112 using the same deployment mechanism.
|
|
|
|
|
|
==Acknowledgements==
|
|
|
|
Mark Friedenbach for designing and authoring the reference
|
|
implementation of this BIP.
|
|
|
|
Thanks go to Gregory Maxwell who came up with the original idea,
|
|
in #bitcoin-wizards on 2013-07-16.
|
|
|
|
Thomas Kerin authored this BIP document.
|
|
|
|
|
|
==Compatibility==
|
|
|
|
Transactions generated using time-based lock-time will take
|
|
approximately an hour longer to confirm than would be expected under
|
|
the old rules. This is not known to introduce any compatibility
|
|
concerns with existing protocols.
|
|
|
|
|
|
==References==
|
|
|
|
[https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki BIP9: Versionbits]
|
|
|
|
[https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki BIP65: OP_CHECKLOCKTIMEVERIFY]
|
|
|
|
[https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP68: Consensus-enforced transaction replacement signaled via sequence numbers]
|
|
|
|
[https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki BIP112: CHECKSEQUENCEVERIFY]
|
|
|
|
[http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-August/010396.html Softfork deployment considerations]
|
|
|
|
[https://gist.github.com/sipa/bf69659f43e763540550 Version bits]
|
|
|
|
|
|
==Copyright==
|
|
|
|
This document is placed in the public domain.
|