Fees are collected strictly on-chain by the shield-pool program into the mint-scoped treasury
PDA. No other component assesses or deducts fees.
Fees apply only to flows that move value out of the pool (publicAmount < 0: withdrawals and
swaps). Deposits and shield-to-shield transfers charge no fee.
Constants
- SOL pool fixed fee:
5_000_000 lamports (0.005 SOL)
- Variable fee (all pools):
gross * 3 / 1000 (0.30%)
- SPL pools (USDC/USDT): variable fee only — no fixed component, charged in the withdrawn token
- Minimum deposit (SOL pool only):
10_000_000 lamports (0.01 SOL); SPL deposits have no
program-enforced minimum
Per-flow behavior
- Deposit (
publicAmount > 0): no fee. The full deposit amount moves into the pool and the
output commitments encode the full amount.
- Shield-to-shield transfer (
publicAmount = 0): no fee. No external value moves; the output
commitments sum to the inputs.
- Withdrawal (
publicAmount < 0): the destination receives net = gross - fee; the treasury
PDA receives fee.
- Swap (
TransactSwap, SOL pool only): fee = fixed + variable is taken from the gross SOL
at the first transaction; the remainder (gross - fee) is what gets swapped.
Fee math
SOL pool (withdraw/swap):
SPL pools (withdraw):
Worked examples
Withdraw 1 SOL (1_000_000_000 lamports) gross:
- Fixed:
5_000_000 lamports
- Variable:
1_000_000_000 * 3 / 1000 = 3_000_000 lamports
- Fee:
8_000_000 lamports — net to recipient: 992_000_000 lamports
Withdraw 100 USDC (100_000_000 base units) gross:
- Variable:
100_000_000 * 3 / 1000 = 300_000 base units (0.30 USDC)
- Fee:
300_000 base units — net to recipient: 99_700_000 base units
The Cloak app presents this in reverse: the user enters what the recipient should receive, and
the app grosses up so net equals the entered amount. At the program level the invariant is
always net = gross - fee.
