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

[Tier Nolan]

On Sun, Nov 1, 2015 at 5:28 PM, jl2012 via bitcoin-dev <
bitcoin-dev at lists.linuxfoundation.org> wrote:

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

There can be unavoidable situations which cause locked coins become
unspendable.

In an ideal world, soft forks that make UTXOs unspendable should increase
the tx version number.  BIP-13 should have done that.  That would make the
change opt-in.

The disabled opcodes like OP_CAT were a DOS/network security change.

Invalidating locked coins is another reason that they shouldn't have been
disabled permanently.

It would have been better to disable them for six months, so at least
people can get their coins back after that.  Inherently, protecting the
network required some limitations being added so that nodes couldn't be
crashed.

For guidelines

* Transaction version numbers will be increased, if possible
* Transactions with unknown/large version numbers are unsafe to use with
locktime
* Reasonable notice is given that the change is being contemplated
* Non-opt-in changes will only be to protect the integrity of the network

Locked transaction that can be validated without excessive load on the
network should be safe to use, even if non-standard.

An OP_CAT script that requires TBs of RAM to validate crosses the threshold
of reasonableness.



>
> 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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>
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