On the contrary, it was stated in a blog post about the intended evolution of Zcash on 15 October 2016, shortly before launch, that one of things that might happen in a âpotentially surprising upgradeâ was to expire dormant funds:
Some of the counterfeit detection schemes weâve considered rely on expiring old, abandoned funds (i.e. users might need to take action to ensure that their dormant funds are not flagged as expired).
It was further stated in the Abstract of ZIP 211, which became active with the Canopy upgrade on 18 November 2020, that the purpose of that ZIP was to âtake a step toward being able to remove the Sprout shielded protocolâ:
This proposal disables the ability to add new value to the Sprout chain value pool balance. This takes a step toward being able to remove the Sprout shielded protocol, thus reducing the overall complexity and attack surface of Zcash.
I completely realize that we shouldnât rely on users having seen a particular 2016 blog post, or a particular ZIP that activated in 2020. But the same message has been repeated consistently by the designers of Zcash to anyone who has ever asked, and whenever the topic has come up. We have not been quiet about it.
ZIP 2004 proposes that v4 transactions be disabled with NU7, and note that even without ZIP 2004 there will be no wallet support for doing so.
This proposal disallows v4 transactions. The v5 transaction format introduced in the NU5 network upgrade does not support Sprout, and so this will have the effect of disabling the ability to spend Sprout funds.
It is not proposed in this ZIP to unissue, burn, or otherwise make Sprout funds permanently unavailable. This leaves open the possibility of re-enabling v4 transactions, or of adding another facility to retrieve these funds if the Zcash community considers it worthwhile. However, since it is possible the ability to spend Sprout funds will never be re-enabled, holders of these funds should move them out of the Sprout pool without delay.
To reiterate: if you have Sprout funds and still have the keys for them, you should move those funds now before you are no longer able to.
I completely agree, but none of the existing pools have been designed for long-term cold storage. Such a pool would have to use different cryptography that is focused on that goal, as opposed to being focused on payments.
One of the reasons why none of Sprout, Sapling, Orchard, or (as of NU7) OrchardZSA are suitable as a long-term cold storage protocol, is that they will be vulnerable to quantum computers when those become viable. I personally no longer think it is âifâ; I estimate that there is a significant chance within the next 3 years that we will be forced to make a decision about whether to also disable the ability to spend Sapling and pre-NU7 Orchard notes.
OrchardZSA is likely to have a âquantum resilienceâ property that allows its notes to be spent safely after any post-quantum transition. Itâs likely that wallets will prioritize non-quantum-resilient notes for spending, so that the vast majority of funds will have been migrated to be quantum-resilient by the time we need to make the decision of whether to disable spending of Sapling and pre-NU7 Orchard notes. But Sapling probably will never be quantum-resilient, and Sprout cannot be.
I will not support any proposal that exposes other pools to unbounded inflation risk due to reimplementing the Sprout shielded protocol.
There might be ways of recovering funds from the Sprout pool that donât expose other pools to unbounded inflation risk from Sprout. Iâm not going to spend any time on that, because the opportunity cost of doing more work on it instead of doing more useful things is huge, even aside from the security risk.
