145 lines
4.2 KiB
Rust
145 lines
4.2 KiB
Rust
use std::fmt::{self, Debug};
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#[cfg(any(test, feature = "test-impl"))]
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use hex::FromHex;
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use crate::{Challenge, Ciphersuite, Element, Error, Group, Signature};
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#[cfg(feature = "serde")]
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use crate::serialization::ElementSerialization;
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/// A valid verifying key for Schnorr signatures over a FROST [`Ciphersuite::Group`].
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#[derive(Copy, Clone, PartialEq, Eq)]
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#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
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#[cfg_attr(feature = "serde", serde(bound = "C: Ciphersuite"))]
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#[cfg_attr(feature = "serde", serde(try_from = "ElementSerialization<C>"))]
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#[cfg_attr(feature = "serde", serde(into = "ElementSerialization<C>"))]
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pub struct VerifyingKey<C>
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where
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C: Ciphersuite,
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{
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pub(crate) element: Element<C>,
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}
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impl<C> VerifyingKey<C>
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where
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C: Ciphersuite,
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{
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/// Create a new VerifyingKey from the given element.
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#[cfg_attr(feature = "internals", visibility::make(pub))]
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#[cfg_attr(docsrs, doc(cfg(feature = "internals")))]
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pub(crate) fn new(element: <C::Group as Group>::Element) -> Self {
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Self { element }
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}
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/// Return the underlying element.
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#[cfg(feature = "internals")]
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pub fn to_element(self) -> <C::Group as Group>::Element {
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self.element
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}
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/// Deserialize from bytes
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pub fn deserialize(
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bytes: <C::Group as Group>::Serialization,
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) -> Result<VerifyingKey<C>, Error<C>> {
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<C::Group>::deserialize(&bytes)
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.map(|element| VerifyingKey { element })
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.map_err(|e| e.into())
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}
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/// Serialize `VerifyingKey` to bytes
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pub fn serialize(&self) -> <C::Group as Group>::Serialization {
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<C::Group>::serialize(&self.element)
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}
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/// Verify a purported `signature` with a pre-hashed [`Challenge`] made by this verification
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/// key.
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pub(crate) fn verify_prehashed(
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&self,
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challenge: Challenge<C>,
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signature: &Signature<C>,
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) -> Result<(), Error<C>> {
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// Verify check is h * ( - z * B + R + c * A) == 0
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// h * ( z * B - c * A - R) == 0
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//
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// where h is the cofactor
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let zB = C::Group::generator() * signature.z;
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let cA = self.element * challenge.0;
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let check = (zB - cA - signature.R) * C::Group::cofactor();
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if check == C::Group::identity() {
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Ok(())
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} else {
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Err(Error::InvalidSignature)
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}
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}
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/// Verify a purported `signature` over `msg` made by this verification key.
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pub fn verify(&self, msg: &[u8], signature: &Signature<C>) -> Result<(), Error<C>> {
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C::verify_signature(msg, signature, self)
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}
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/// Computes the group public key given the group commitment.
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#[cfg_attr(feature = "internals", visibility::make(pub))]
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pub(crate) fn from_commitment(
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commitment: &crate::keys::VerifiableSecretSharingCommitment<C>,
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) -> Result<VerifyingKey<C>, Error<C>> {
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Ok(VerifyingKey {
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element: commitment
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.coefficients()
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.first()
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.ok_or(Error::IncorrectCommitment)?
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.value(),
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})
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}
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}
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impl<C> Debug for VerifyingKey<C>
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where
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C: Ciphersuite,
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{
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.debug_tuple("VerifyingKey")
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.field(&hex::encode(self.serialize()))
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.finish()
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}
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}
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#[cfg(any(test, feature = "test-impl"))]
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impl<C> FromHex for VerifyingKey<C>
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where
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C: Ciphersuite,
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{
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type Error = &'static str;
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fn from_hex<T: AsRef<[u8]>>(hex: T) -> Result<Self, Self::Error> {
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let v: Vec<u8> = FromHex::from_hex(hex).map_err(|_| "invalid hex")?;
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match v.try_into() {
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Ok(bytes) => Self::deserialize(bytes).map_err(|_| "malformed verifying key encoding"),
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Err(_) => Err("malformed verifying key encoding"),
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}
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}
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}
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#[cfg(feature = "serde")]
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impl<C> TryFrom<ElementSerialization<C>> for VerifyingKey<C>
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where
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C: Ciphersuite,
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{
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type Error = Error<C>;
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fn try_from(value: ElementSerialization<C>) -> Result<Self, Self::Error> {
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Self::deserialize(value.0)
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}
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}
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#[cfg(feature = "serde")]
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impl<C> From<VerifyingKey<C>> for ElementSerialization<C>
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where
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C: Ciphersuite,
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{
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fn from(value: VerifyingKey<C>) -> Self {
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Self(value.serialize())
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}
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}
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