When shielding to the MASP (i.e. has transparent inputs), an additional flat fee should be paid. In the first implementation, this will fee will be sent to PGF. The fee amount will be a protocol parameter.

The current task list consists of:

• Add fee data to the MASP tx. This can just be an authorizing signature. In theory, anyone should be able to pay this fee. This must be hardened against replay attempts however.
• Change the tx generation functions and cli to allow signing over this fee.
• Change the tx generation functions and cli to check that the user can pay the fee before broadcasting.
• Change the user vp so that it correctly authorizes the fee payment. I think this can be implemented by adding another MaspAction::MaspAuthorizer action to be fed into the vp.
• Add a parameter for the fee. This should be changeable via governance.
• Change the MASP vp to enfore the payment of a fee when shielding
• The protocol needs to be changed to actually affect the fee payment.
• This might require changes to the ledger app
• Issue Make IBC shielding support shielding fees #4754