The use of tx version field in BIP62 and 68

The use of tx version field in BIP62 and 68
2015-08-08 18:56 ` Mark Friedenbach
  
From: jl2012 @ 2015-08-08 18:51 UTC (permalink / raw)
  To: bitcoin-dev

BIP68 rules and some of the BIP62 rules are applied only if the tx 
version is >=2 and >=3 respectively. Therefore, it is not possible to 
create a tx which follows BIP62 but not BIP68. If we introduce v4 tx 
later, BIP62 and BIP68 will all become mandatory.

Some rules, e.g. "scriptPubKey evaluation will be required to result in 
a single non-zero value" in BIP62, will cause trouble when we try to 
introduce a new script system with softfork.

I suggest to divide the tx version field into 2 parts: the higher 4 bits 
and lower 28 bits.

BIP62 is active for a tx if its highest bits are 0000, and the second 
lowest bit is 1.

BIP68 is active for a tx if its highest bits are 0000, and the third 
lowest bit is 1.

So it will be easier for us to re-purpose the nSequence, or to take 
advantage of malleability in the future. If this is adopted, the 
nSequence high bit requirement in BIP68 becomes unnecessary as we could 
easily switch it off.

The low bits will allow 28 independent BIPs and should be ample for many 
years. When they are exhausted, we can switch the high bits to a 
different number (1-15) and redefine the meaning of low bits. By that 
time, some of the 28 BIPs might have become obsoleted or could be 
merged.

(I'm not sure if there are other draft BIPs with similar interpretation 
of tx version but the comments above should also apply to them)


 permalink raw reply	[|nested]
2015-08-08 18:51 [bitcoin-dev] The use of tx version field in BIP62 and 68 jl2012

  2015-08-08 19:18   ` jl2012
  
From: Mark Friedenbach @ 2015-08-08 18:56 UTC (permalink / raw)
  To: jl2012;  Bitcoin Dev

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It is not a bug that you are unable to selectively choose these features
with higher version numbers. The version selection is in there at all
because there is a possibility that there exists already signed
transactions which would violate these new rules. We wouldn't want these
transactions to become unspendable. However moving forward there is no
reason to selectively pick and choose which of these new consensus rules
you want to apply your transaction.
On Aug 8, 2015 11:51 AM, "jl2012 via bitcoin-dev" <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> BIP68 rules and some of the BIP62 rules are applied only if the tx version
> is >=2 and >=3 respectively. Therefore, it is not possible to create a tx
> which follows BIP62 but not BIP68. If we introduce v4 tx later, BIP62 and
> BIP68 will all become mandatory.
>
> Some rules, e.g. "scriptPubKey evaluation will be required to result in a
> single non-zero value" in BIP62, will cause trouble when we try to
> introduce a new script system with softfork.
>
> I suggest to divide the tx version field into 2 parts: the higher 4 bits
> and lower 28 bits.
>
> BIP62 is active for a tx if its highest bits are 0000, and the second
> lowest bit is 1.
>
> BIP68 is active for a tx if its highest bits are 0000, and the third
> lowest bit is 1.
>
> So it will be easier for us to re-purpose the nSequence, or to take
> advantage of malleability in the future. If this is adopted, the nSequence
> high bit requirement in BIP68 becomes unnecessary as we could easily switch
> it off.
>
> The low bits will allow 28 independent BIPs and should be ample for many
> years. When they are exhausted, we can switch the high bits to a different
> number (1-15) and redefine the meaning of low bits. By that time, some of
> the 28 BIPs might have become obsoleted or could be merged.
>
> (I'm not sure if there are other draft BIPs with similar interpretation of
> tx version but the comments above should also apply to them)
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists•linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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 permalink raw reply	[|nested]
2015-08-08 18:56 ` Mark Friedenbach

  
From: jl2012 @ 2015-08-08 19:18 UTC ( / )
  To: Mark Friedenbach;  Bitcoin Dev

I think I have explained my motivation but let me try to make it 
clearer.

For example, BIP62 says "scriptPubKey evaluation will be required to 
result in a single non-zero value". If we had BIP62 before BIP16, P2SH 
could not be done in the current form because BIP16 leaves more than one 
element on the stake for non-upgrading nodes. BIP17 also violates BIP62.

BIP68 is "only enforced if the most significant bit of the sequence 
number field is set.", so it is optional, anyway. All I do is to move 
the flag from sequence number to version number.

The blocksize debate shows how a permanent softfork may cause trouble 
later. We need to be very careful when doing further softforks, making 
sure we will have enough flexibility for further development.

Mark Friedenbach 於 2015-08-08 14:56 寫到:
> It is not a bug that you are unable to selectively choose these
> features with higher version numbers. The version selection is in
> there at all because there is a possibility that there exists already
> signed transactions which would violate these new rules. We wouldn't
> want these transactions to become unspendable. However moving forward
> there is no reason to selectively pick and choose which of these new
> consensus rules you want to apply your transaction.
> On Aug 8, 2015 11:51 AM, "jl2012 via bitcoin-dev"
> <bitcoin-dev@lists•linuxfoundation.org> wrote:
> 
>> BIP68 rules and some of the BIP62 rules are applied only if the tx
>> version is >=2 and >=3 respectively. Therefore, it is not possible
>> to create a tx which follows BIP62 but not BIP68. If we introduce v4
>> tx later, BIP62 and BIP68 will all become mandatory.
>> 
>> Some rules, e.g. "scriptPubKey evaluation will be required to
>> result in a single non-zero value" in BIP62, will cause trouble when
>> we try to introduce a new script system with softfork.
>> 
>> I suggest to divide the tx version field into 2 parts: the higher 4
>> bits and lower 28 bits.
>> 
>> BIP62 is active for a tx if its highest bits are 0000, and the
>> second lowest bit is 1.
>> 
>> BIP68 is active for a tx if its highest bits are 0000, and the
>> third lowest bit is 1.
>> 
>> So it will be easier for us to re-purpose the nSequence, or to take
>> advantage of malleability in the future. If this is adopted, the
>> nSequence high bit requirement in BIP68 becomes unnecessary as we
>> could easily switch it off.
>> 
>> The low bits will allow 28 independent BIPs and should be ample for
>> many years. When they are exhausted, we can switch the high bits to
>> a different number (1-15) and redefine the meaning of low bits. By
>> that time, some of the 28 BIPs might have become obsoleted or could
>> be merged.
>> 
>> (I'm not sure if there are other draft BIPs with similar
>> interpretation of tx version but the comments above should also
>> apply to them)
>> _______________________________________________
>> bitcoin-dev mailing list
>> bitcoin-dev@lists•linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev [1]
> 
> 
> Links:
> ------
> [1] https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev