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brentstone committed Nov 14, 2024
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Expand Up @@ -123,9 +123,11 @@ This **might** incentivise validators to prioritise this transaction above those

## Paying fees with tokens in the MASP

It is also possible to pay for fees using the MASP when dealing with a transfer transaction involving shielded inputs (shielded, and unshielding transfers both natively and with IBC): this is required to prevent information leakage which defeats the purpose of the shielded pool.
It is also possible to pay for fees using the MASP when dealing with a transaction involving shielded inputs (shielded and unshielding transfers both natively and over IBC).
This is a good practice when trying to maximize data protection and minimize information leakage.

When dealing with MASP fee payment, the client will try to deduct the fees from the spending key specfied by `--gas-spending-key` of the shielded transaction and unshield them to the transparent balance of the `--gas-payer` (or the address corresponding to the first key in the `--signing-keys`) before being paid to the block proposer.
When dealing with MASP fee payment, the client will first try to deduct the fees from the spending key specfied by `--gas-spending-key` of the shielded transaction and unshield them to the transparent balance of the `--gas-payer` (or the address corresponding to the first key in the `--signing-keys`).
Then, these fees are paid to the block proposer from the gas payer.

For example, if the user has a spending key `spending-key-1` in their wallet, and they want to pay for the fees of a shielded transfer transaction using the MASP, they would run the following command:

Expand Down Expand Up @@ -158,11 +160,11 @@ So it is requried to unshield just the difference between the gas cost and the t
### Using a disposable gas payer (recommended)

It is also possible to use a disposable gas payer to pay for transaction fees.
This is useful (and recommended) in cases where the user does not want to leak information and reveal the identity of the `--gas-payer` to prevent correlation.
This is useful (and recommended) in cases where the user does not want to leak information and reveal the identity of the `--gas-payer`.
In order to use a disposable gas payer, the user must include the `--disposable-gas-payer` flag.
The fees will be deducted from the shielded balance of the shielded transactions `--gas-spending-key` and unshielded to the transparent balance of an ephemeral transparent address before being paid by the ephemeral address.

For example, if the user has the same two spending keys from the previous example in their wallet, and they want to pay for the fees of an unshield transfer transaction using a disposable address, they would run the following command:
For example, if the user has the same two spending keys from the previous example in their wallet, and they want to pay for the fees of an unshield transaction using a disposable address, they would run the following command:

```shell copy
namadac unshield \
Expand All @@ -182,17 +184,23 @@ To prevent spamming the network, the protocol establishes a maximum gas limit (`
namadac query-protocol-parameters
```

If the transaction exceeds this limit it won't be accepted: the protocol sets a value which should allow for most transactions to be accepted. Should the user be in need to submit a more complex (and therefore gas-demanding) transaction, there are two ways around it, both taking advantage of the fact that the protocol gas limit only applies to the first transaction of the batch.
If the transaction exceeds this limit it won't be accepted; as such, the protocol sets a value that should allow for most transactions to be accepted. Should the user be in need to submit a more complex (and therefore gas-demanding) transaction, there are two ways around it, both taking advantage of the fact that the protocol gas limit only applies to the first transaction of the batch.

1. The user can submit a batch of two transactions: the first one just unshields the necessary funds to pay fees for the entire batch whereas the second transaction applies the desired transfer. Since the protocol gas limit only applies to the first transaction of the batch (the one paying fees), the second transaction is free from this limit and can be as complex as required (withing the size and gas limits of the entire block)
2. The user can submit a first transaction paying fees via the MASP. This time though, the transaction unshields an amount which is enough to cover both the gas fees of itself and of the desired MASP transaction. After this, the gas payer of the first transaction will still have a transparent balance large enough to cover fees for a second MASP transaction that actually performs the desired transfer and does not require any more fee unshielding.
1. The user can submit a batch of two transactions: the first one just unshields the necessary funds to pay fees for the entire batch, while the second transaction applies the desired transfer.
Since the protocol gas limit only applies to the first transaction of the batch (the one paying fees), the second transaction is free from this limit and can be as complex as required (within the size and gas limits of the entire block).

2. The user can submit a first transaction paying fees via the MASP. This time though, the transaction unshields an amount that is enough to cover both the gas fees of itself and of the desired MASP transaction.
After this, the gas payer of the first transaction will still have a transparent balance large enough to cover fees for a second MASP transaction that actually performs the desired transfer and does not require any more fee unshielding.

<Callout type="info">
The first solution proposed above is currently not supported by the CLI client and requires direct usage of the SDK.
</Callout>

Each of these solutions has its own advanatages and drawbacks compared to the other one. Using a single batch with two transactions allows for faster confirmation times and lower gas costs (since a batch will cost less than two separate transactions), but because of the way the SDK builds MASP transactions it could fail sometimes (specifically the SDK invalidates notes that have been spent by the first transaction in the batch which could cause a lack of funds for the second one). Using two separate transactions instead, avoids this issue (since the user can call `shielded-sync` after the first one to recollect all the available funds), but requires more gas overall and longer confirmation times.
Each of these solutions has its own advanatages and drawbacks compared to the other one.
Using a single batch with two transactions allows for faster confirmation times and lower gas costs (since a batch will cost less than two separate transactions), but because of the way the SDK builds MASP transactions, it could fail sometimes (specifically the SDK invalidates notes that have been spent by the first transaction in the batch, which could cause a lack of funds for the second one).
Using two separate transactions instead avoids this issue (since the user can call `shielded-sync` after the first one to recollect all the available funds), but requires more gas overall and longer confirmation times.

<Callout type="warning">
It is also possible, using either of the two solutions presetend above, to use MASP fee payment to pay fees for non-MASP transactions. Please note that this is discouraged since it could establish a linkage between the MASP transaction and the entity behind the non-MASP transactions.
It is also possible, using either of the two solutions presented above, to use MASP fee payment to pay fees for non-MASP transactions.
Please note that this is discouraged since it could establish a linkage between the MASP transaction and the entity behind the non-MASP transactions.
</Callout>

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