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fix(frost-secp256k1-tr): empty merkle root tweak should still hash the x-only pk #815

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merged 1 commit into from
Dec 30, 2024
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fix(frost-secp256k1-tr): empty merkle root tweak should still hash the x-only pk #815

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27 changes: 11 additions & 16 deletions frost-secp256k1-tr/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -208,7 +208,11 @@ fn tweak<T: AsRef<[u8]>>(
merkle_root: Option<T>,
) -> Scalar {
match merkle_root {
None => Secp256K1ScalarField::zero(),
None => {
let mut hasher = tagged_hash("TapTweak");
hasher.update(public_key.to_affine().x());
hasher_to_scalar(hasher)
}
Some(root) => {
let mut hasher = tagged_hash("TapTweak");
hasher.update(public_key.to_affine().x());
Expand Down Expand Up @@ -481,10 +485,9 @@ impl Ciphersuite for Secp256K1Sha256TR {
// > key should commit to an unspendable script path instead of having
// > no script path. This can be achieved by computing the output key
// > point as Q = P + int(hashTapTweak(bytes(P)))G.
let merkle_root = [0u8; 0];
Ok((
key_package.tweak(Some(&merkle_root)),
public_key_package.tweak(Some(&merkle_root)),
key_package.tweak::<&[u8]>(None),
public_key_package.tweak::<&[u8]>(None),
))
}
}
Expand Down Expand Up @@ -862,12 +865,8 @@ pub mod round2 {
key_package: &keys::KeyPackage,
merkle_root: Option<&[u8]>,
) -> Result<SignatureShare, Error> {
if merkle_root.is_some() {
let key_package = key_package.clone().tweak(merkle_root);
frost::round2::sign(signing_package, signer_nonces, &key_package)
} else {
frost::round2::sign(signing_package, signer_nonces, key_package)
}
let key_package = key_package.clone().tweak(merkle_root);
frost::round2::sign(signing_package, signer_nonces, &key_package)
}
}

Expand Down Expand Up @@ -904,12 +903,8 @@ pub fn aggregate_with_tweak(
public_key_package: &keys::PublicKeyPackage,
merkle_root: Option<&[u8]>,
) -> Result<Signature, Error> {
if merkle_root.is_some() {
let public_key_package = public_key_package.clone().tweak(merkle_root);
frost::aggregate(signing_package, signature_shares, &public_key_package)
} else {
frost::aggregate(signing_package, signature_shares, public_key_package)
}
let public_key_package = public_key_package.clone().tweak(merkle_root);
frost::aggregate(signing_package, signature_shares, &public_key_package)
}

/// A signing key for a Schnorr signature on FROST(secp256k1, SHA-256).
Expand Down
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