327 lines
11 KiB
Rust
327 lines
11 KiB
Rust
//! Rerandomized FROST with Jubjub curve.
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#![allow(non_snake_case)]
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#![deny(missing_docs)]
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use group::GroupEncoding;
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#[cfg(feature = "alloc")]
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use group::{ff::Field as FFField, ff::PrimeField};
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use frost_rerandomized::{
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frost_core::{frost, Ciphersuite, Field, FieldError, Group, GroupError},
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RandomizedParams,
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};
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use rand_core::{CryptoRng, RngCore};
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use crate::{hash::HStar, private::Sealed, sapling};
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/// An error type for the FROST(Jubjub, BLAKE2b-512) ciphersuite.
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pub type Error = frost_rerandomized::frost_core::Error<JubjubBlake2b512>;
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/// An implementation of the FROST(Jubjub, BLAKE2b-512) ciphersuite scalar field.
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#[derive(Clone, Copy)]
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pub struct JubjubScalarField;
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impl Field for JubjubScalarField {
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type Scalar = jubjub::Scalar;
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type Serialization = [u8; 32];
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fn zero() -> Self::Scalar {
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Self::Scalar::zero()
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}
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fn one() -> Self::Scalar {
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Self::Scalar::one()
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}
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fn invert(scalar: &Self::Scalar) -> Result<Self::Scalar, FieldError> {
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// [`Jubjub::Scalar`]'s Eq/PartialEq does a constant-time comparison using
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// `ConstantTimeEq`
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if *scalar == <Self as Field>::zero() {
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Err(FieldError::InvalidZeroScalar)
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} else {
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Ok(Self::Scalar::invert(scalar).unwrap())
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}
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}
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fn random<R: RngCore + CryptoRng>(rng: &mut R) -> Self::Scalar {
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Self::Scalar::random(rng)
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}
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fn serialize(scalar: &Self::Scalar) -> Self::Serialization {
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scalar.to_bytes()
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}
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fn little_endian_serialize(scalar: &Self::Scalar) -> Self::Serialization {
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Self::serialize(scalar)
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}
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fn deserialize(buf: &Self::Serialization) -> Result<Self::Scalar, FieldError> {
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match Self::Scalar::from_repr(*buf).into() {
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Some(s) => Ok(s),
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None => Err(FieldError::MalformedScalar),
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}
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}
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}
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/// An implementation of the FROST(Jubjub, BLAKE2b-512) ciphersuite group.
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#[derive(Clone, Copy, PartialEq, Eq)]
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pub struct JubjubGroup;
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impl Group for JubjubGroup {
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type Field = JubjubScalarField;
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type Element = jubjub::ExtendedPoint;
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type Serialization = [u8; 32];
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fn cofactor() -> <Self::Field as Field>::Scalar {
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Self::Field::one()
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}
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fn identity() -> Self::Element {
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Self::Element::identity()
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}
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fn generator() -> Self::Element {
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sapling::SpendAuth::basepoint()
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}
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fn serialize(element: &Self::Element) -> Self::Serialization {
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element.to_bytes()
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}
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fn deserialize(buf: &Self::Serialization) -> Result<Self::Element, GroupError> {
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let point = Self::Element::from_bytes(buf);
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match Option::<Self::Element>::from(point) {
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Some(point) => {
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if point == Self::identity() {
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Err(GroupError::InvalidIdentityElement)
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} else if point.is_torsion_free().into() {
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Ok(point)
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} else {
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Err(GroupError::InvalidNonPrimeOrderElement)
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}
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}
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None => Err(GroupError::MalformedElement),
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}
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}
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}
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/// An implementation of the FROST(Jubjub, BLAKE2b-512) ciphersuite.
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#[derive(Clone, Copy, PartialEq, Eq, Debug)]
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pub struct JubjubBlake2b512;
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impl Ciphersuite for JubjubBlake2b512 {
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type Group = JubjubGroup;
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type HashOutput = [u8; 64];
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type SignatureSerialization = [u8; 64];
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/// H1 for FROST(Jubjub, BLAKE2b-512)
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fn H1(m: &[u8]) -> <<Self::Group as Group>::Field as Field>::Scalar {
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HStar::<sapling::SpendAuth>::new(b"FROST_RedJubjubR")
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.update(m)
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.finalize()
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}
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/// H2 for FROST(Jubjub, BLAKE2b-512)
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fn H2(m: &[u8]) -> <<Self::Group as Group>::Field as Field>::Scalar {
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HStar::<sapling::SpendAuth>::default().update(m).finalize()
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}
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/// H3 for FROST(Jubjub, BLAKE2b-512)
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fn H3(m: &[u8]) -> <<Self::Group as Group>::Field as Field>::Scalar {
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HStar::<sapling::SpendAuth>::new(b"FROST_RedJubjubN")
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.update(m)
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.finalize()
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}
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/// H4 for FROST(Jubjub, BLAKE2b-512)
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fn H4(m: &[u8]) -> Self::HashOutput {
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let mut state = blake2b_simd::Params::new()
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.hash_length(64)
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.personal(b"FROST_RedJubjubM")
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.to_state();
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*state.update(m).finalize().as_array()
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}
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/// H5 for FROST(Jubjub, BLAKE2b-512)
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fn H5(m: &[u8]) -> Self::HashOutput {
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let mut state = blake2b_simd::Params::new()
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.hash_length(64)
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.personal(b"FROST_RedJubjubC")
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.to_state();
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*state.update(m).finalize().as_array()
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}
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/// HDKG for FROST(Jubjub, BLAKE2b-512)
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fn HDKG(m: &[u8]) -> Option<<<Self::Group as Group>::Field as Field>::Scalar> {
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Some(
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HStar::<sapling::SpendAuth>::new(b"FROST_RedJubjubD")
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.update(m)
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.finalize(),
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)
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}
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}
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// Shorthand alias for the ciphersuite
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type J = JubjubBlake2b512;
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/// A FROST(Jubjub, BLAKE2b-512) participant identifier.
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pub type Identifier = frost::Identifier<J>;
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/// FROST(Jubjub, BLAKE2b-512) keys, key generation, key shares.
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pub mod keys {
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use alloc::vec::Vec;
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use super::*;
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/// Allows all participants' keys to be generated using a central, trusted
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/// dealer.
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pub fn keygen_with_dealer<RNG: RngCore + CryptoRng>(
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max_signers: u16,
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min_signers: u16,
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mut rng: RNG,
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) -> Result<(Vec<SecretShare>, PublicKeyPackage), Error> {
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frost::keys::keygen_with_dealer(max_signers, min_signers, &mut rng)
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}
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/// Secret and public key material generated by a dealer performing
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/// [`keygen_with_dealer`].
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///
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/// # Security
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///
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/// To derive a FROST(Jubjub, BLAKE2b-512) keypair, the receiver of the [`SecretShare`] *must* call
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/// .into(), which under the hood also performs validation.
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pub type SecretShare = frost::keys::SecretShare<J>;
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/// A FROST(Jubjub, BLAKE2b-512) keypair, which can be generated either by a trusted dealer or using
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/// a DKG.
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///
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/// When using a central dealer, [`SecretShare`]s are distributed to
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/// participants, who then perform verification, before deriving
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/// [`KeyPackage`]s, which they store to later use during signing.
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pub type KeyPackage = frost::keys::KeyPackage<J>;
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/// Public data that contains all the signers' public keys as well as the
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/// group public key.
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///
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/// Used for verification purposes before publishing a signature.
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pub type PublicKeyPackage = frost::keys::PublicKeyPackage<J>;
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}
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/// FROST(Jubjub, BLAKE2b-512) Round 1 functionality and types.
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pub mod round1 {
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use frost_rerandomized::frost_core::frost::keys::SigningShare;
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use super::*;
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/// Comprised of FROST(Jubjub, BLAKE2b-512) hiding and binding nonces.
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///
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/// Note that [`SigningNonces`] must be used *only once* for a signing
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/// operation; re-using nonces will result in leakage of a signer's long-lived
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/// signing key.
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pub type SigningNonces = frost::round1::SigningNonces<J>;
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/// Published by each participant in the first round of the signing protocol.
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///
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/// This step can be batched if desired by the implementation. Each
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/// SigningCommitment can be used for exactly *one* signature.
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pub type SigningCommitments = frost::round1::SigningCommitments<J>;
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/// Performed once by each participant selected for the signing operation.
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///
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/// Generates the signing nonces and commitments to be used in the signing
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/// operation.
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pub fn commit<RNG>(
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participant_identifier: frost::Identifier<J>,
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secret: &SigningShare<J>,
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rng: &mut RNG,
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) -> (SigningNonces, SigningCommitments)
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where
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RNG: CryptoRng + RngCore,
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{
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frost::round1::commit::<J, RNG>(participant_identifier, secret, rng)
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}
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}
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/// Generated by the coordinator of the signing operation and distributed to
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/// each signing party.
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pub type SigningPackage = frost::SigningPackage<J>;
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/// FROST(Jubjub, BLAKE2b-512) Round 2 functionality and types, for signature share generation.
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pub mod round2 {
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use super::*;
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/// A FROST(Jubjub, BLAKE2b-512) participant's signature share, which the Coordinator will aggregate with all other signer's
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/// shares into the joint signature.
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pub type SignatureShare = frost::round2::SignatureShare<J>;
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/// Generated by the coordinator of the signing operation and distributed to
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/// each signing party
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pub type SigningPackage = frost::SigningPackage<J>;
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/// Performed once by each participant selected for the signing operation.
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///
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/// Receives the message to be signed and a set of signing commitments and a set
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/// of randomizing commitments to be used in that signing operation, including
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/// that for this participant.
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///
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/// Assumes the participant has already determined which nonce corresponds with
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/// the commitment that was assigned by the coordinator in the SigningPackage.
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pub fn sign(
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signing_package: &SigningPackage,
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signer_nonces: &round1::SigningNonces,
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key_package: &keys::KeyPackage,
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randomizer_point: &<<J as Ciphersuite>::Group as Group>::Element,
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) -> Result<SignatureShare, Error> {
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frost_rerandomized::sign(
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signing_package,
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signer_nonces,
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key_package,
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randomizer_point,
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)
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}
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}
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/// A Schnorr signature on FROST(Jubjub, BLAKE2b-512).
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pub type Signature = frost_rerandomized::frost_core::Signature<J>;
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/// Verifies each FROST(Jubjub, BLAKE2b-512) participant's signature share, and if all are valid,
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/// aggregates the shares into a signature to publish.
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///
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/// Resulting signature is compatible with verification of a plain Schnorr
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/// signature.
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///
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/// This operation is performed by a coordinator that can communicate with all
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/// the signing participants before publishing the final signature. The
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/// coordinator can be one of the participants or a semi-trusted third party
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/// (who is trusted to not perform denial of service attacks, but does not learn
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/// any secret information). Note that because the coordinator is trusted to
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/// report misbehaving parties in order to avoid publishing an invalid
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/// signature, if the coordinator themselves is a signer and misbehaves, they
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/// can avoid that step. However, at worst, this results in a denial of
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/// service attack due to publishing an invalid signature.
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pub fn aggregate(
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signing_package: &round2::SigningPackage,
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signature_shares: &[round2::SignatureShare],
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pubkeys: &keys::PublicKeyPackage,
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randomized_params: &RandomizedParams<J>,
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) -> Result<Signature, Error> {
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frost_rerandomized::aggregate(
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signing_package,
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signature_shares,
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pubkeys,
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randomized_params,
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)
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}
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/// A signing key for a Schnorr signature on FROST(Jubjub, BLAKE2b-512).
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pub type SigningKey = frost_rerandomized::frost_core::SigningKey<J>;
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/// A valid verifying key for Schnorr signatures on FROST(Jubjub, BLAKE2b-512).
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pub type VerifyingKey = frost_rerandomized::frost_core::VerifyingKey<J>;
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