Re: [bitcoin-dev] Compatibility requirements for hard or soft forks

[jl2012@xbt.hk]

My answer is simply "No", you don't have to maintain backward 
compatibility for non-standard tx.

The same question applies to P2SH. Before the deployment of BIP16, one 
could have created a time-locked tx with one of the output was in the 
form of HASH160 <hash> EQUAL. The <hash>, however, is not a hash of a 
valid serialized script, so the output is now permanently frozen.

It also applies to all the OP codes disabled by Satoshi: one could have 
created a time-locked tx with those now disabled OP codes.

Same for BIP65 with the use of OP_NOP2. Following your logic, we can't 
make any softfork related to the script system.

I think it is very important to make it clear that non-standard txs and 
non-standard scripts may become invalid in the future

Gavin Andresen via bitcoin-dev 於 2015-10-28 10:06 寫到:
> I'm hoping this fits under the moderation rule of "short-term changes
> to the Bitcoin protcol" (I'm not exactly clear on what is meant by
> "short-term"; it would be lovely if the moderators would start a
> thread on bitcoin-discuss to clarify that):
> 
> Should it be a requirement that ANY one-megabyte transaction that is
> valid
> under the existing rules also be valid under new rules?
> 
> Pro:  There could be expensive-to-validate transactions created and
> given a
> lockTime in the future stored somewhere safe. Their owners may have no
> other way of spending the funds (they might have thrown away the
> private
> keys), and changing validation rules to be more strict so that those
> transactions are invalid would be an unacceptable confiscation of
> funds.
> 
> Con: It is extremely unlikely there are any such large, timelocked
> transactions, because the Core code has had a clear policy for years
> that
> 100,000-byte transactions are &quot;standard&quot; and are relayed and
> mined, and
> larger transactions are not. The requirement should be relaxed so that
> only
> valid 100,000-byte transaction under old consensus rules must be valid
> under new consensus rules (larger transactions may or may not be
> valid).
> 
> I had to wrestle with that question when I implemented BIP101/Bitcoin
> XT
> when deciding on a limit for signature hashing (and decided the right
> answer was to support any "non-attack"1MB transaction; see
> https://bitcoincore.org/~gavin/ValidationSanity.pdf [1] for more
> details).
> 
> --
> 
> --
> Gavin Andresen
> 
> 
> Links:
> ------
> [1] https://bitcoincore.org/~gavin/ValidationSanity.pdf
> 
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