Support stealth address mode

[Keith-CY]

Stealth Address is an interesting use case of UTXO and is a prospective feature of Neuron(and Nexus).

We can take a brief look at its definition and use cases. Then if you are interested, go deeper.

Ref: https://www.investopedia.com/terms/s/stealth-address-cryptocurrency.asp

cc @yanguoyu @JeffreyMa597 @homura @zhangyouxin @IronLu233 @zhb666 @Danie0918

[Keith-CY]

We may start stealth address mode with light client because light client has limited ability to on-chain data, while stealth address limits the usage of HD wallet.

For instance, in stealth mode, the path of address generation is predictable, so light client doesn't have to subscribe to all addresses simultaneously, and once a transaction is bound to an address, it could be marked as used and removed from the subscription.

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Here're the core rules:

In stealth address mode,

1. A set of addresses will be generated in obfuscated sequence(by a specific rule). At any given time, only one address is active for the user.
2. When the first relevant transaction is synchronized, the address is regarded as revealed on-chain, and a block countdown timer starts for this address (the countdown range can be customized).
3. When the countdown ends, the wallet activates the next address, deactivates the previous one as used(should be invisible), and unsubscribes it after several blocks.

[Keith-CY]

Some details were added at #100 (comment)

Please check if it's feasible.

Besides, the stealth mode should also be considered in Nexus because the rule of key generation is going to be the same. @homura

[zhangyouxin]

After reading about Monero Steal Address and bitcoin steal address, I think the current neuron wallet has provided some privacy with advantage of UTXO model and BIP32, because a user need extended-pubkey to view all incomming transactions, which is equivilant to view key in Monero. The key difference here is that user should use address that is not revealed on-chain to receive assets

So I have some questions for the core rule here:

• Is the steal mode in neuron aiming to use an address only once to receive token?
• how to generate a steal address by sender when given a receiver public address?
• why is there a block count down after an address is revealed?

[homura]

An unpublished proposal for Bitcoin

[Keith-CY]

So I have some questions for the core rule here:

• Is the steal mode in neuron aiming to use an address only once to receive token?

Yes, each address is expected to be a one-time address, but it's hard to reject transfers to a specific address, so a countdown will be introduced to freeze the address, as mentioned in point 2 and 3 at #100 (comment)

• how to generate a steal address by sender when given a receiver public address?

I've considered concealing the address against the third party, but we can have a talk about it

• why is there a block count down after an address is revealed?

It's for the light client mode, it's up to 500 scripts to subscribe with the light client so the activated addresses should be limited. With the countdown, we can keep the group of subscribed scripts small