Suggestion: Solve year 2106 problem by taking timestamps mod 2^32

Currently, Bitcoin's timestamp rules are as follows:

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)

Thus, Bitcoin will "die" on or about 2106-02-07, when there is no timestamp below 2^32 that exceeds the median of the last 11 blocks.

If the rules were changed to the following, this problem would be solved:

1. The block timestamp plus k*2^32 may not be lower than the median of the last 11 blocks' 2. The block timestamp plus k*2^32 may not be greater than the current time plus two hours 3. k is an integer, whose value must be the same for the calculations of Rule 1 and Rule 2

This would cause a hardfork in the year 2106, which is approximately 85.5 years from now, by which time 95% of nodes would hopefully have updated.

Another proposed solution is 64-bit timestamps. They would break compatibility with other software that has specific expectations of header fields, like ASICs' firmware. They would also cause a hardfork before the date of timestamp overflow. I thus believe them to be a less appropriate solution.

What do you think of this idea? Is it worth a BIP?

On Saturday, September 19, 2020 5:36 AM, yanmaani--- via bitcoin-dev <bitcoin-dev@lists•linuxfoundation•org> wrote:

> Currently, Bitcoin's timestamp rules are as follows:
>
> 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)
>
>     Thus, Bitcoin will "die" on or about 2106-02-07, when there is no
>     timestamp below 2^32 that exceeds the median of the last 11 blocks.
>
>     If the rules were changed to the following, this problem would be
>     solved:
>
> 4.  The block timestamp plus k*2^32 may not be lower than the median of
>     the last 11 blocks'
>
> 5.  The block timestamp plus k*2^32 may not be greater than the current
>     time plus two hours
>
> 6.  k is an integer, whose value must be the same for the calculations of
>     Rule 1 and Rule 2

I believe that is equivalent to: we treat block headers (as abstract data structure) as having a 64-bit timestamp, which have the requirement that the difference between the timestamp and the median timestamp of the past 11 blocks is at least one and at most 2^32 (I don't think we need to support less than 6 blocks per 136 years).

On serialization, only the lower 32 bit are encoded. On deserialization, the higher 32 bits are set equal to that of the median of the past 11 blocks. If that violates the rule above, set it one higher.

That's in line of how I'd expect this will eventually be addressed. There is no rush, of course.

>     What do you think of this idea? Is it worth a BIP?

Probably, at some point.

Cheers,