Unlinkable Angor project identifiers

[dangershony]

To break the ability to link a transaction to the Angor protocol we should use the same techniques as silent payments.

[dangershony]

MetacoSA/NBitcoin#1240

[dangershony]

This is the plan.
(inspired by the silent payment design bip352)

Creating the project identifier, the founder uses their private key to create a shared secret
A = founder key
B = angor key
P = project identifier key

Let P = B + hash(a·B)·G
Encode P as an Angor identifier with bech32 prefix angor+pubkey (on the blockchain it will be a P2WPK output)

Spending the fee in the Angor Identifier address

Let p = b + hash(A·b)·G

p is the private key that can spend the coins in the Angor address
P can only generated by the founder and angor key.
p can only be generated by angor key.