Re: [bitcoin-dev] Year 2038 problem and year 2106 chain halting

[Kate Salazar <mercedes.catherine.salazar@gmail.com>]

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Hi, BIP 42 is a code base consensus soft fork that at the time of
activation does not really manifest as a fork because nobody is running any
code not already applying it. Can a similar thing be done in 17 years? (I
haven't really made sense of this year 2038 problem, I don't know or
understand what is required if there's something to be done).
Cheers!

On Sat, Oct 16, 2021 at 11:00 PM David Bakin via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> yes but ... just for the sake of argument ... if a change such as this
> wraparound interpretation is made anytime in the next 5 years it'll be over
> a *decade after that *before any wrapped-around timestamp is legitimately
> mined ... and by then nobody will be running incompatible (decade old) node
> software (especially since it would mean that a decade had gone by without
> a *single* consensus change ... seems very unlikely).
>
> On Sat, Oct 16, 2021 at 11:57 AM vjudeu via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> > What happens if a series of blocks has a timestamp of 0xFFFFFFFF at the
>> appropriate time?
>>
>> The chain will halt for all old clients, because there is no 32-bit value
>> greater than 0xffffffff.
>>
>> > 1. Is not violated, since "not lower than" means "greater than or equal
>> to"
>>
>> No, because it has to be strictly "greater than" in the Bitcoin Core
>> source code, it is rejected when it is "lower or equal to", see:
>> https://github.com/bitcoin/bitcoin/blob/6f0cbc75be7644c276650fd98bfdb6358b827399/src/validation.cpp#L3089-L3094
>>
>> > 2. Is not violated, since it would be a past actual real time.
>>
>> If the current time is 0x0000000100000000, then the lowest 32 bits will
>> point to some time around 1970, so for old clients two rules are violated
>> at the same time.
>>
>> > 3. Is not violated since 0xFFFFFFFF < 0x100000000.
>>
>> This is hard to change, because 32-bit timestamps are included in block
>> headers, so using any wider data type here will make it
>> hardware-incompatible and will cause a hard-fork. That's why I think new
>> timestamps should be placed in the coinbase transaction. But that still
>> does not solve chain halting problem.
>>
>> To test chain halting, all that is needed is starting regtest and
>> producing one block with 0xffffffff timestamp, just after the Genesis
>> Block. Then, median time is equal to 0xffffffff and adding any new blocks
>> is no longer possible. The only soft-fork solution I can see require
>> overwriting that block.
>>
>> Example from https://bitcointalk.org/index.php?topic=5365359.0
>>
>> submitblock
>> 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
>> null
>> generatetoaddress 1 mpXwg4jMtRhuSpVq4xS3HFHmCmWp9NyGKt
>> CreateNewBlock: TestBlockValidity failed: time-too-old, block's timestamp
>> is too early (code -1)
>>
>> I don't know any timestamp that can be used in any next block and
>> accepted by old nodes.
>>
>> On 2021-10-16 01:01:54 user ZmnSCPxj <ZmnSCPxj@protonmail.com> wrote:
>> > Good morning yanmaani,
>>
>>
>> > It's well-known. Nobody really cares, because it's so far off. Not
>> > possible to do by softfork, no.
>>
>> I think it is possible by softfork if we try hard enough?
>>
>>
>> > 1.  The block timestamp may not be lower than the median of the last 11
>> >     blocks'
>> >
>> > 2.  The block timestamp may not be greater than the current time plus
>> two
>> >     hours
>> >
>> > 3.  The block timestamp may not be greater than 2^32 (Sun, 07 Feb 2106
>> >     06:28:16 +0000)
>>
>> What happens if a series of blocks has a timestamp of 0xFFFFFFFF at the
>> appropriate time?
>>
>> In that case:
>>
>> 1.  Is not violated, since "not lower than" means "greater than or equal
>> to", and after a while the median becomes 0xFFFFFFFF and 0xFFFFFFFF ==
>> 0xFFFFFFFF
>> 2.  Is not violated, since it would be a past actual real time.
>> 3.  Is not violated since 0xFFFFFFFF < 0x100000000.
>>
>> In that case, we could then add an additional rule, which is that a
>> 64-bit (or 128-bit, or 256-bit) timestamp has to be present in the coinbase
>> transaction, with similar rules except translated to 64-bit/128-bit/256-bit.
>>
>> Possibly a similar scheme could be used for `nLockTime`; we could put a
>> 64-bit `nLockTime64` in that additional signed block in Taproot SegWit v1
>> if the legacy v`nLockTime` is at the maximum seconds-timelock possible.
>>
>> Regards,
>> ZmnSCPxj
>>
>>
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