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[program] Reorder confidential transfer fee harvest logic to terminate early when possible #749

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Merged
samkim-crypto merged 2 commits into from
Sep 30, 2025
Merged

[program] Reorder confidential transfer fee harvest logic to terminate early when possible #749

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54ac31f
reorder harvest logic to terminate early when possible
samkim-crypto Sep 30, 2025
826604d
remove unnecessary mut
samkim-crypto Sep 30, 2025
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53 changes: 30 additions & 23 deletions program/src/extension/confidential_transfer_fee/processor.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -196,7 +196,7 @@ fn process_withdraw_withheld_tokens_from_accounts(
// unnecessary check, but helps for clarity
check_program_account(mint_account_info.owner)?;
let mut mint_data = mint_account_info.data.borrow_mut();
let mut mint = PodStateWithExtensionsMut::<PodMint>::unpack(&mut mint_data)?;
let mint = PodStateWithExtensionsMut::<PodMint>::unpack(&mut mint_data)?;

// mint must be extended for fees
let transfer_fee_config = mint.get_extension::<TransferFeeConfig>()?;
Expand All @@ -221,6 +221,33 @@ fn process_withdraw_withheld_tokens_from_accounts(
return Err(TokenError::AccountFrozen.into());
}

// summation of withheld amount ciphertexts is expensive, so do all preliminary
// checks before the summation
{
let destination_confidential_transfer_account =
destination_account.get_extension::<ConfidentialTransferAccount>()?;
destination_confidential_transfer_account.valid_as_destination()?;

// The funds are moved from the accounts to a destination account. Here, the
// `source` equates to the withdraw withheld authority associated in the
// mint.

// Checks that the withdraw authority ElGamal public key associated with the
// mint is consistent with what was actually used to generate the zkp.
let confidential_transfer_fee_config =
mint.get_extension::<ConfidentialTransferFeeConfig>()?;
if proof_context.first_pubkey
!= confidential_transfer_fee_config.withdraw_withheld_authority_elgamal_pubkey
{
return Err(TokenError::ConfidentialTransferElGamalPubkeyMismatch.into());
}
// Checks that the ElGamal public key associated with the destination account is
// consistent with what was actually used to generate the zkp.
if proof_context.second_pubkey != destination_confidential_transfer_account.elgamal_pubkey {
return Err(TokenError::ConfidentialTransferElGamalPubkeyMismatch.into());
}
} // free `destination_confidential_transfer_account`

// Sum up the withheld amounts in all the accounts.
let mut aggregate_withheld_amount = EncryptedWithheldAmount::zeroed();
for account_info in &account_infos[num_signers..] {
Expand Down Expand Up @@ -254,28 +281,6 @@ fn process_withdraw_withheld_tokens_from_accounts(
}
}

let destination_confidential_transfer_account =
destination_account.get_extension_mut::<ConfidentialTransferAccount>()?;
destination_confidential_transfer_account.valid_as_destination()?;

// The funds are moved from the accounts to a destination account. Here, the
// `source` equates to the withdraw withheld authority associated in the
// mint.

// Checks that the withdraw authority ElGamal public key associated with the
// mint is consistent with what was actually used to generate the zkp.
let confidential_transfer_fee_config =
mint.get_extension_mut::<ConfidentialTransferFeeConfig>()?;
if proof_context.first_pubkey
!= confidential_transfer_fee_config.withdraw_withheld_authority_elgamal_pubkey
{
return Err(TokenError::ConfidentialTransferElGamalPubkeyMismatch.into());
}
// Checks that the ElGamal public key associated with the destination account is
// consistent with what was actually used to generate the zkp.
if proof_context.second_pubkey != destination_confidential_transfer_account.elgamal_pubkey {
return Err(TokenError::ConfidentialTransferElGamalPubkeyMismatch.into());
}
// Checks that the withheld amount ciphertext is consistent with the ciphertext
// data that was actually used to generate the zkp.
if proof_context.first_ciphertext != aggregate_withheld_amount {
Expand All @@ -285,6 +290,8 @@ fn process_withdraw_withheld_tokens_from_accounts(
// The proof data contains the mint withheld amount encrypted under the
// destination ElGamal pubkey. This amount is added to the destination
// available balance.
let destination_confidential_transfer_account =
destination_account.get_extension_mut::<ConfidentialTransferAccount>()?;
destination_confidential_transfer_account.available_balance = ciphertext_arithmetic::add(
&destination_confidential_transfer_account.available_balance,
&proof_context.second_ciphertext,
Expand Down
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