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Diffstat (limited to 'bip-0068.mediawiki')
| -rw-r--r-- | bip-0068.mediawiki | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/bip-0068.mediawiki b/bip-0068.mediawiki index e336765..28df807 100644 --- a/bip-0068.mediawiki +++ b/bip-0068.mediawiki @@ -13,15 +13,15 @@ This BIP describes a modification to the consensus-enforced semantics of the seq ==Motivation== -Bitcoin has sequence number fields for each input of a transaction. The original idea appears to have been that the highest sequence number should dominate and miners should prefer it over lower sequence numbers. This was never really implemented, and the half-implemented code seemed to be making this assumption that miners would honestly prefer the higher sequence numbers, even if the lower ones were much much more profitable. That turns out to be a dangerous assumption, and so most technical people have assumed that kind of sequence number mediated replacement was useless because there was no way to enforce "honest" behavior, as even a few rational (profit maximizing) miners would break that completely. The change described by this BIP provides the missing piece that makes sequence numbers do something significant with respect to enforcing transaction replacement without assuming anything other than profit-maximizing behavior on the part of miners. +Bitcoin has sequence number fields for each input of a transaction. The original idea appears to have been that the highest sequence number should dominate and miners should prefer it over lower sequence numbers. This was never really implemented, and the half-implemented code seemed to be making an assumption that miners would honestly prefer the higher sequence numbers, even if the lower ones were much much more profitable. That turns out to be a dangerous assumption, and so most technical people have assumed that kind of sequence number mediated replacement was useless because there was no way to enforce "honest" behavior, as even a few rational (profit maximizing) miners would break that completely. The change described by this BIP provides the missing piece that makes sequence numbers do something significant with respect to enforcing transaction replacement without assuming anything other than profit-maximizing behavior on the part of miners. ==Specification== For transactions with an nVersion of 2 or greater, if the most significant bit (1 << 31) of a sequence number is clear, the remaining 31 bits are interpreted as an encoded relative lock-time. A sequence number with the most significant bit set is given no consensus meaning and can be included in any block, like normal, under all circumstances. -If the second most significant bit (1 << 30) is clear, the remaining bits reduced by 2^14 are interpreted as a minimum block-heigh constraint over the input's age. A sequence number of zero indicates a relative lock-time of zero blocks (bits 31 and 30 clear) and can be included in any block. A sequence number of 1 << 14 can be included in the next block after the input it is spending, or any block thereafter, rather than it being possible to be included in the same block. A sequence number of 2 << 14 can't be included until two blocks later, and so on. +If the second most significant bit (1 << 30) is clear, the next 16 bits are interpreted as a minimum block-height constraint over the input's age. The remaining 14 bits have no consensus-enforced meaning. A sequence number of zero indicates a relative lock-time of zero blocks (bits 31 and 30 clear) and can be included in any block. A sequence number of 1 << 14 can be included in the next block after the input it is spending, or any block thereafter, but cannot be included in the same block as its parent. A sequence number of 2 << 14 can't be included until at least two blocks later, and so on. -Alternatively, if the second most significant bit (1 << 30) is set, the remaining bits reduced by 2^5 are interpreted as a minimum block-time constraint over the input's age. A sequence number with just that second most significant bit set (0x40000000) is interpreted as a relative lock-time of 0, measured in seconds, and can be included in the same block as the output being spent. Advancing that sequence number by 2^5 (0x40000020) constrains the transaction to be included in blocks with an nTime timestamp at least one second greater than the median time stamp of the 11 blocks prior to the block containing the coin being spent. Advancing the sequence number by an additional 2^5 (0x40000040) constrains the spend to be two seconds later, and so on. +Alternatively, if the second most significant bit (1 << 30) is set, the next 25 bits are interpreted as a minimum block-time constraint over the input's age. The remaining 5 bits have no consensus-enforced meaning. A sequence number with just that second most significant bit set (0x40000000) is interpreted as a relative lock-time of 0, measured in seconds, and can be included in the same block as the output being spent. Advancing that sequence number by 2^5 (0x40000020) constrains the transaction to be included in blocks with an nTime timestamp at least one second greater than the median time stamp of the 11 blocks prior to the block containing the coin being spent. Advancing the sequence number by an additional 2^5 (0x40000040) constrains the spend to be two seconds later, and so on. This is proposed to be accomplished by replacing IsFinalTx() and CheckFinalTx(), existing consensus and non-consensus code functions that return true if a transaction's lock-time constraints are satisfied and false otherwise, with LockTime() and CheckLockTime(), new functions that return a non-zero value if a transaction's lock-time or sequence number constraints are not satisfied and zero otherwise: |