[ZIP 252] Network Upgrade 5

[teor2345]

This is an initial draft of the NU 5 ZIP, based on ZIP-251 - Canopy.

Changes from Canopy

I have made the following changes:

• split out zcashd-specific behaviour
• describe Zebra-specific behaviour
• guess versions for zcashd and Zebra
• pick a random consensus branch ID
• increment network protocol versions
• pick network upgrade heights based on:
  • https://electriccoin.co/blog/network-upgrade-pipeline-2-0/
  • US/EU common work hours
  • a quick calculation

Remaining Work

• Choose NU5 ZIPs
• Update transaction version backward compatibility if ZIP 225 is accepted
• Update zcashd section
• Update Zebra section
• Update references

Optional

• Pick a name for NU5

[daira]

Thanks! :-)

[teor2345]

Might as well add all the draft zips as proposed?

[teor2345]

This copied text is wrong, v4 and v5 transactions are both supported after NU5.

Should we also say something about the consensus branch ID rejecting v4 transactions created before NU5 activation? (Is that correct?)

Suggested change

	defines a new transaction version. NU5 transactions are therefore in the new
	v5 format specified by [#zip-0225]_. Therefore, pre-NU5 transactions are
	structurally invalid after NU5 activation: they can not be parsed correctly
	by pre-NU5 nodes.
	defines a new transaction version. Therefore, NU5 transactions MAY be in
	the new v5 format specified by [#zip-0225]_. Unlike previous transaction
	version updates, the pre-NU5 v4 transaction format remains valid after
	NU5 activation. Both transaction formats MUST be accepted by NU5
	nodes.
	v5 transactions MUST be used for:
	- Orchard transfers
	- non-malleable transaction IDs
	v4 transactions MUST be used for:
	- Sprout transfers
	Transactions that don't need these features can use either format.

[nuttycom]

The v4 transactions MUST be used for Sprout Transfers is a modification that we hadn't talked about before, but I think that this could be a good idea; we could entirely remove Sprout support from the V5 transaction format in that case.

[teor2345]

Sounds good, how do we even make decisions like this? 🤷

[nuttycom]

@teor2345 I've added this as a possible alternative to ZIP 225 in #453

[r3ld3v]

Sounds good, how do we even make decisions like this? 🤷

I'll make sure we discuss it at the Arborist call on the 11th.