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

Suggestion: Solve year 2106 problem by taking timestamps mod 2^32
2020-10-16 21:58 ` Pieter Wuille
  
From: yanmaani @ 2020-09-19 12:36 UTC (permalink / raw)
  To: Bitcoin Protocol Discussion

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?


 permalink raw reply	[|nested]
2020-09-19 12:36 [bitcoin-dev] Suggestion: Solve year 2106 problem by taking timestamps mod 2^32 yanmaani

  
From: Pieter Wuille @ 2020-10-16 21:58 UTC ( / )
  To: yanmaani, Bitcoin Protocol Discussion

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,

--
Pieter