Note that this violates present assumptions about transaction validity, unless a constraint also exists that any output of such an expiry block is not spent for at least 100 blocks.

Do you have a clean way of ensuring this?

On Thu, Sep 17, 2015 at 2:41 PM, jl2012 via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

Fill-or-kill tx is not a new idea and is discussed in the Scaling Bitcoin workshop. In Satoshi's implementation of nLockTime, a huge range of timestamp (from 1970 to 2009) is wasted. By exploiting this unused range and with compromise in the time resolution, a fill-or-kill system could be built with a softfork.

-----------
Two new parameters, nLockTime2 and nKillTime are defined:

nLockTime2 (Range: 0-1,853,010)
0: Tx could be confirmed at or after block 420,000
1: Tx could be confirmed at or after block 420,004
.
.
719,999: Tx could be confirmed at or after block 3,299,996 (about 55 years from now)
720,000: Tx could be confirmed if the median time-past >= 1,474,562,048 (2016-09-22)
720,001: Tx could be confirmed if the median time-past >= 1,474,564,096 (2016-09-22)
.
.
1,853,010 (max): Tx could be confirmed if the median time-past >= 3,794,966,528 (2090-04-04)

nKillTime (Range: 0-2047)
if nLockTime2 < 720,000, the tx could be confirmed at or before block (nLockTime2 + nKillTime * 4)
if nLockTime2 >= 720,000, the tx could be confirmed if the median time-past <= (nLockTime2 - 720,001 + nKillTime) * 2048

Finally, nLockTime = 500,000,000 + nKillTime + nLockTime2 * 2048

Setting a bit flag in tx nVersion will activate the new rules.

The resolution is 4 blocks or 2048s (34m)
The maximum confirmation window is 8188 blocks (56.9 days) or 16,769,024s (48.5 days)

For example:
With nLockTime2 = 20 and nKillTime = 100, a tx could be confirmed only between block 420,080 and 420,480
With nLockTime2 = 730,000 and nKillTime = 1000, a tx could be confirmed only between median time-past of 1,495,042,048 and 1,497,090,048

----------------
Why is this a softfork?

Remember this formula: nLockTime = 500,000,000 + nKillTime + nLockTime2 * 2048

For height based nLockTime2 (<= 719,999)

For nLockTime2 = 0 and nKillTime = 0, nLockTime = 500,000,000, which means the tx could be confirmed after 1970-01-01 with the original lock time rule. As the new rule does not allow confirmation until block 420,000, it's clearly a softfork.

It is not difficult to see that the growth of nLockTime will never catch up nLockTime2.

At nLockTime2 = 719,999 and nKillTime = 2047, nLockTime = 1,974,559,999, which means 2016-09-22. However, the new rule will not allow confirmation until block 3,299,996 which is decades to go



For time based nLockTime2 (> 720,000)

For nLockTime2 = 720,000 and nKillTime = 0, nLockTime = 1,974,560,000, which means the tx could be confirmed after median time-past 1,474,560,000 (assuming BIP113). However, the new rule will not allow confirmation until 1,474,562,048, therefore a soft fork.

For nLockTime2 = 720,000 and nKillTime = 2047, nLockTime = 1,974,562,047, which could be confirmed at 1,474,562,047. Again, the new rule will not allow confirmation until 1,474,562,048. The 1 second difference makes it a soft fork.

Actually, for every nLockTime2 value >= 720,000, the lock time with the new rule must be 1-2048 seconds later than the original rule.

For nLockTime2 = 1,853,010 and nKillTime = 2047, nLockTime = 4,294,966,527, which is the highest possible value with the 32-bit nLockTime

----------------
User's perspective:

A user wants his tx either filled or killed in about 3 hours. He will set a time-based nLockTime2 according to the current median time-past, and set nKillTime = 5

A user wants his tx get confirmed in the block 630000, the first block with reward below 10BTC. He is willing to pay high fee but don't want it gets into another block. He will set nLockTime2 = 210,000 and nKillTime = 0

----------------
OP_CLTV

Time-based OP_CLTV could be upgraded to support time-based nLockTime2. However, height-based OP_CLTV is not compatible with nLockTime2. To spend a height-based OP_CLTV output, user must use the original nLockTime.

We may need a new OP_CLTV2 which could verify both nLockTime and nLockTime2

----------------
55 years after?

The height-based nLockTime2 will overflow in 55 years. It is very likely a hard fork will happen to implement a better fill-or-kill system. If not, we could reboot everything with another tx nVersion for another 55 years.


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