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zk-token-sdk: remove non-constant time assign for fee_proof transcript (#27354)

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samkim-crypto 2022-08-24 14:25:09 +09:00 committed by GitHub
parent 3b01517da6
commit 804dfe0f1a
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1 changed files with 24 additions and 16 deletions
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40
zk-token-sdk/src/sigma_proofs/fee_proof.rs
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@ -40,6 +40,9 @@ impl FeeSigmaProof {
/// Creates a fee sigma proof assuming that the committed fee is greater than the maximum fee
/// bound.
///
/// Note: the proof is generated twice via `create_proof_fee_above_max` and
/// `create_proof_fee_below_max` to enforce constant time execution.
///
/// * `(fee_amount, fee_commitment, fee_opening)` - The amount, Pedersen commitment, and
/// opening of the transfer fee
/// * `(delta_fee, delta_commitment, delta_opening)` - The amount, Pedersen commitment, and
@ -76,24 +79,29 @@ impl FeeSigmaProof {
let below_max = u64::ct_gt(&max_fee, &fee_amount);
// conditionally assign transcript; transcript is not conditionally selectable
if bool::from(below_max) {
*transcript = transcript_fee_below_max;
} else {
*transcript = transcript_fee_above_max;
}
// choose one of `proof_fee_above_max` or `proof_fee_below_max` according to whether the
// fee amount surpasses max fee
let fee_max_proof = FeeMaxProof::conditional_select(
&proof_fee_above_max.fee_max_proof,
&proof_fee_below_max.fee_max_proof,
below_max,
);
let fee_equality_proof = FeeEqualityProof::conditional_select(
&proof_fee_above_max.fee_equality_proof,
&proof_fee_below_max.fee_equality_proof,
below_max,
);
transcript.append_point(b"Y_max_proof", &fee_max_proof.Y_max_proof);
transcript.append_point(b"Y_delta", &fee_equality_proof.Y_delta);
transcript.append_point(b"Y_claimed", &fee_equality_proof.Y_claimed);
transcript.challenge_scalar(b"c");
transcript.challenge_scalar(b"w");
Self {
fee_max_proof: FeeMaxProof::conditional_select(
&proof_fee_above_max.fee_max_proof,
&proof_fee_below_max.fee_max_proof,
below_max,
),
fee_equality_proof: FeeEqualityProof::conditional_select(
&proof_fee_above_max.fee_equality_proof,
&proof_fee_below_max.fee_equality_proof,
below_max,
),
fee_max_proof,
fee_equality_proof,
}
}