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fix taproot crate #1

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Merged
zebra-lucky merged 5 commits into from
Dec 27, 2023
Merged

fix taproot crate #1

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b493931
fix tweaked pubkey
mimoo Dec 13, 2023
c880c6e
fix signature
mimoo Dec 13, 2023
a55eabb
fix signature (bus)
mimoo Dec 13, 2023
c518726
fix signature (bis bis)
mimoo Dec 13, 2023
ba34a4e
fix signature (bis bis bis)
mimoo Dec 13, 2023
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29 changes: 26 additions & 3 deletions frost-secp256k1-tr/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -228,6 +228,17 @@ pub fn tweaked_public_key(
ProjectivePoint::GENERATOR * tweak(&pk, merkle_root) + pk
}

/// Creates a real BIP341 tweaked public key by assuming an even y-coordinate.
pub fn real_tweaked_pubkey(
public_key: &<<Secp256K1Sha256 as Ciphersuite>::Group as Group>::Element,
merkle_root: &[u8],
) -> <<Secp256K1Sha256 as Ciphersuite>::Group as Group>::Element {
let tweaked_pubkey = tweaked_public_key(public_key, merkle_root);
AffinePoint::decompact(&tweaked_pubkey.to_affine().x())
.unwrap()
.into()
}

/// Create a BIP341 compliant tweaked secret key
pub fn tweaked_secret_key(
secret: <<<Secp256K1Sha256 as Ciphersuite>::Group as Group>::Field as Field>::Scalar,
Expand Down Expand Up @@ -325,7 +336,13 @@ impl Ciphersuite for Secp256K1Sha256 {
verifying_key: &Element<S>,
) -> <<Self::Group as Group>::Field as Field>::Scalar {
let t = tweak(&verifying_key, &[]);
z + t * challenge.clone().to_scalar()
let tc = t * challenge.clone().to_scalar();
let tweaked_pubkey = tweaked_public_key(&verifying_key, &[]);
if tweaked_pubkey.to_affine().y_is_odd().into() {
z - tc
} else {
z + tc
}
}

/// compute tweaked signature_share
Expand All @@ -343,7 +360,13 @@ impl Ciphersuite for Secp256K1Sha256 {
}

let mut kp = key_package.clone();
if key_package.verifying_key().y_is_odd() {
let public_key = key_package.verifying_key();
let pubkey_is_odd = public_key.y_is_odd();
let tweaked_pubkey_is_odd = tweaked_public_key(public_key.element(), &[])
.to_affine()
.y_is_odd()
.into();
if pubkey_is_odd != tweaked_pubkey_is_odd {
kp.negate_signing_share();
}

Expand All @@ -354,7 +377,7 @@ impl Ciphersuite for Secp256K1Sha256 {
fn tweaked_public_key(
public_key: &<Self::Group as Group>::Element,
) -> <Self::Group as Group>::Element {
tweaked_public_key(public_key, &[])
real_tweaked_pubkey(public_key, &[])
}

/// calculate tweaked R
Expand Down