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[confidential-transfer] Use the value 0 for claimed delta when transfer fee is max fee #506

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[confidential-transfer] Use the value 0 for claimed delta when transfer fee is max fee #506

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18 changes: 11 additions & 7 deletions confidential-transfer/proof-generation/src/transfer_with_fee.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -186,12 +186,16 @@ pub fn transfer_with_fee_split_proof_data(
// calculate fee
let transfer_fee_basis_points = fee_rate_basis_points;
let transfer_fee_maximum_fee = maximum_fee;
let (raw_fee_amount, delta_fee) = calculate_fee(transfer_amount, transfer_fee_basis_points)
let (raw_fee_amount, raw_delta_fee) = calculate_fee(transfer_amount, transfer_fee_basis_points)
.ok_or(TokenProofGenerationError::FeeCalculation)?;

// if raw fee is greater than the maximum fee, then use the maximum fee for the
// fee amount
let fee_amount = std::cmp::min(transfer_fee_maximum_fee, raw_fee_amount);
// fee amount and set the claimed delta fee to be 0 for simplicity
let (fee_amount, claimed_delta_fee) = if transfer_fee_maximum_fee < raw_fee_amount {
(transfer_fee_maximum_fee, 0)
} else {
(raw_fee_amount, raw_delta_fee)
};

// split and encrypt fee
let (fee_amount_lo, fee_amount_hi) = try_split_u64(fee_amount, FEE_AMOUNT_LO_BITS)
Expand Down Expand Up @@ -232,7 +236,7 @@ pub fn transfer_with_fee_split_proof_data(
.ok_or(TokenProofGenerationError::IllegalAmountBitLength)?;

// compute claimed and real delta commitment
let (claimed_commitment, claimed_opening) = Pedersen::new(delta_fee);
let (claimed_commitment, claimed_opening) = Pedersen::new(claimed_delta_fee);
let (delta_commitment, delta_opening) = compute_delta_commitment_and_opening(
(
&combined_transfer_amount_commitment,
Expand All @@ -249,7 +253,7 @@ pub fn transfer_with_fee_split_proof_data(
fee_amount,
&delta_commitment,
&delta_opening,
delta_fee,
claimed_delta_fee,
&claimed_commitment,
&claimed_opening,
transfer_fee_maximum_fee,
Expand Down Expand Up @@ -310,7 +314,7 @@ pub fn transfer_with_fee_split_proof_data(

// generate range proof data
let delta_fee_complement = MAX_FEE_BASIS_POINTS
.checked_sub(delta_fee)
.checked_sub(claimed_delta_fee)
.ok_or(TokenProofGenerationError::FeeCalculation)?;

let max_fee_basis_points_commitment =
Expand All @@ -334,7 +338,7 @@ pub fn transfer_with_fee_split_proof_data(
new_decrypted_available_balance,
transfer_amount_lo,
transfer_amount_hi,
delta_fee,
claimed_delta_fee,
delta_fee_complement,
fee_amount_lo,
fee_amount_hi,
Expand Down