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//! The MuSig2 multisignature scheme.
//!
//! ## Synopsis
//!
//! ```
//! # use schnorr_fun::binonce::NonceKeyPair;
//! use rand_chacha::ChaCha20Rng;
//! use schnorr_fun::{musig, nonce::Deterministic, Message, Schnorr};
//! use sha2::Sha256;
//! // use sha256 with deterministic nonce generation -- be careful!
//! let musig = musig::new_with_deterministic_nonces::<sha2::Sha256>();
//! // use synthetic nonces with randomness from ThredRng -- harder to make a mistake.
//! let musig = musig::new_with_synthetic_nonces::<sha2::Sha256, rand::rngs::ThreadRng>();
//! // create a keypair
//! use schnorr_fun::fun::Scalar;
//! let my_keypair = musig.new_keypair(Scalar::random(&mut rand::thread_rng()));
//! let public_key1 = my_keypair.public_key();
//! # let kp2 = musig.new_keypair(Scalar::random(&mut rand::thread_rng()));
//! # let public_key2 = kp2.public_key();
//! # let kp3 = musig.new_keypair(Scalar::random(&mut rand::thread_rng()));
//! # let public_key3 = kp3.public_key();
//! // recieve the public keys of all other participants to form the aggregate key.
//! let agg_key = musig
//! .new_agg_key(vec![public_key1, public_key2, public_key3])
//! .into_xonly_key();
//!
//! // create a unique nonce, and send the public nonce to other parties.
//! // ⚠ session_id must be different for every signing attempt
//! let session_id = b"signing-ominous-message-about-banks-attempt-1".as_slice();
//! let mut nonce_rng: ChaCha20Rng =
//! musig.seed_nonce_rng(&agg_key, &my_keypair.secret_key(), session_id);
//! let my_nonce = musig.gen_nonce(&mut nonce_rng);
//! let my_public_nonce = my_nonce.public();
//! # let p2_nonce = NonceKeyPair::random(&mut rand::thread_rng());
//! # let p2_public_nonce = p2_nonce.public();
//! # let p3_nonce = NonceKeyPair::random(&mut rand::thread_rng());
//! # let p3_public_nonce = p3_nonce.public();
//! // collect the public nonces from the other two parties
//! let nonces = vec![my_public_nonce, p2_public_nonce, p3_public_nonce];
//! let message = Message::plain("my-app", b"chancellor on brink of second bailout for banks");
//! // start the signing session
//! let session = musig.start_sign_session(&agg_key, nonces, message);
//! // sign with our single local keypair
//! let my_sig = musig.sign(&agg_key, &session, 0, &my_keypair, my_nonce);
//! # let p2_sig = musig.sign(&agg_key, &session, 1, &kp2, p2_nonce);
//! # let p3_sig = musig.sign(&agg_key, &session, 2, &kp3, p3_nonce);
//! // receive p2_sig and p3_sig from somewhere and check they're valid
//! assert!(musig.verify_partial_signature(&agg_key, &session, 1, p2_sig));
//! assert!(musig.verify_partial_signature(&agg_key, &session, 2, p3_sig));
//! // combine them with ours into the final signature
//! let sig = musig.combine_partial_signatures(&agg_key, &session, [my_sig, p2_sig, p3_sig]);
//! // check it's a valid normal Schnorr signature
//! musig
//! .schnorr
//! .verify(&agg_key.agg_public_key(), message, &sig);
//! ```
//!
//! ## Description
//!
//! The MuSig2 multisignature scheme lets you aggregate multiple public keys into a single public
//! key that requires all of the corresponding secret keys to authorize a signature under the aggregate key.
//!
//! See [the excellent paper] for the abstract details of the protocol and security proofs. **⚠ THIS
//! IS EXPERIMENTAL⚠** it is currently compatible with [this
//! version](https://github.com/jonasnick/bips/blob/musig2/bip-musig2.mediawiki) of the
//! specification.
//!
//! **⚠ THIS IS EXPERIMENTAL⚠** it is currently compatible with [this PR](https://github.com/jonasnick/bips/pull/37) to the specification.
//! However, we go "off-spec" in a few places especially with regards to nonce generation where we provide our own APIs (that
//! at the time of writing are subject to change).
//!
//! [the excellent paper]: https://eprint.iacr.org/2020/1261.pdf
//! [secp256k1-zkp]: https://github.com/ElementsProject/secp256k1-zkp/pull/131
pub use crate::binonce::{Nonce, NonceKeyPair};
use crate::{adaptor::EncryptedSignature, Message, Schnorr, Signature};
use alloc::vec::Vec;
use secp256kfun::{
digest::{generic_array::typenum::U32, Digest},
g,
hash::{HashAdd, Tag},
marker::*,
nonce::{self, NoNonces, NonceGen},
rand_core::{RngCore, SeedableRng},
s, KeyPair, Point, Scalar, G,
};
/// The MuSig context.
pub struct MuSig<H, NG> {
/// The hash used to compress the key list to 32 bytes.
pk_hash: H,
/// The hash used to generate each key's coefficient.
coeff_hash: H,
/// The hash used to generate the nonce coefficients.
nonce_coeff_hash: H,
/// The instance of the underlying Schnorr context.
pub schnorr: Schnorr<H, NG>,
/// The nonce generator used to
nonce_gen: NG,
}
impl<H, NG> MuSig<H, NG> {
/// Create a new keypair.
///
/// A shorthand for [`KeyPair::new`].
///
/// [`KeyPair::new`]: KeyPair::<Normal>::new
pub fn new_keypair(&self, secret_key: Scalar) -> KeyPair {
KeyPair::<Normal>::new(secret_key)
}
/// Gets the nonce generator from the underlying Schnorr instance.
pub fn nonce_gen(&self) -> &NG {
&self.nonce_gen
}
/// Generate nonces for creating signatures shares.
///
/// ⚠ You must use a CAREFULLY CHOSEN nonce rng, see [`MuSig::seed_nonce_rng`]
pub fn gen_nonce<R: RngCore>(&self, nonce_rng: &mut R) -> NonceKeyPair {
NonceKeyPair::random(nonce_rng)
}
}
impl<H, NG> MuSig<H, NG>
where
H: Tag + Default,
NG: Tag + Clone,
{
/// Create a new MuSig instance from a [`Schnorr`] instance.
///
/// The MuSig instnace will clone and tag the schnorr instance's `nonce_gen` for its own use.
pub fn new(schnorr: Schnorr<H, NG>) -> Self {
Self {
pk_hash: H::default().tag(b"KeyAgg list"),
coeff_hash: H::default().tag(b"KeyAgg coefficient"),
nonce_coeff_hash: H::default().tag(b"MuSig/noncecoef"),
nonce_gen: schnorr.nonce_gen().clone().tag(b"MuSig"),
schnorr,
}
}
}
impl<H, NG> Default for MuSig<H, NG>
where
H: Tag + Default,
NG: Default + Clone + Tag,
{
fn default() -> Self {
MuSig::new(Schnorr::<H, NG>::default())
}
}
/// A list of keys aggregated into a single key.
///
/// Created using [`MuSig::new_agg_key`].
///
/// The `AggKey` can't be serialized but it's very efficient to re-create it from the initial list of keys.
///
/// [`MuSig::new_agg_key`]
#[derive(Debug, Clone)]
pub struct AggKey<T> {
/// The keys involved in the key aggregation.
keys: Vec<Point>,
/// The coefficients of each key
coefs: Vec<Scalar<Public>>,
/// Whether the secret keys needs to be negated when signing
needs_negation: bool,
/// The aggregate key
agg_key: Point<T>,
/// The tweak on the aggregate key
tweak: Scalar<Public, Zero>,
}
impl<T: Copy> AggKey<T> {
/// The aggregate key.
///
/// Note that before using it as a key in a system that accepts "x-only" keys like `[BIP341]`
/// you must call [`into_xonly_key`] and use that aggregate key.
///
/// [`into_xonly_key`]: Self::into_xonly_key
pub fn agg_public_key(&self) -> Point<T> {
self.agg_key
}
/// An iterator over the **public keys** of each party in the aggregate key.
pub fn keys(&self) -> impl Iterator<Item = Point> + '_ {
self.keys.iter().copied()
}
}
impl AggKey<Normal> {
/// Convert the key into a BIP340 AggKey.
///
/// This is the [BIP340] x-only version of the key which you can put in a segwitv1 output
/// and create/verify BIP340 signatures under.
///
/// [BIP340]: https://bips.xyz/340
pub fn into_xonly_key(self) -> AggKey<EvenY> {
let (agg_key, needs_negation) = self.agg_key.into_point_with_even_y();
let mut tweak = self.tweak;
tweak.conditional_negate(needs_negation);
AggKey {
keys: self.keys,
coefs: self.coefs,
needs_negation,
tweak,
agg_key,
}
}
/// Add a scalar `tweak` to aggregate MuSig public key.
///
/// The resulting key is equal to the existing key plus `tweak * G`. The tweak mutates the
/// public key while still allowing the original set of signers to sign under the new key.
/// This function is appropriate for doing [BIP32] tweaks before calling `into_xonly_key`.
/// It **is not** appropriate for doing taproot tweaking which must be done on an [`AggKey`]
/// with [`EvenY`] public key in BIP340 form, see [`into_xonly_key`].
///
/// ## Return value
///
/// In the erroneous case that the tweak is exactly equal to the negation of the aggregate
/// secret key it returns `None`.
///
/// [BIP32]: https://bips.xyz/32
/// [`AggKey`]: crate::musig::AggKey
/// [`into_xonly_key`]: crate::musig::AggKey::into_xonly_key
pub fn tweak(self, tweak: Scalar<impl Secrecy, impl ZeroChoice>) -> Option<Self> {
let agg_key = g!(self.agg_key + tweak * G).normalize().non_zero()?;
let tweak = s!(self.tweak + tweak).public();
Some(AggKey {
keys: self.keys,
coefs: self.coefs,
needs_negation: false,
agg_key,
tweak,
})
}
}
// /// A [`AggKey`] that has been converted into a [BIP340] x-only key.
// ///
// /// [BIP340]: https://bips.xyz/340
impl AggKey<EvenY> {
/// Applies an "x-only" tweak to the aggregate key.
///
/// This function exists to allow for [BIP341] tweaks to the aggregate public key.
///
/// [BIP341]: https://bips.xyz/341
pub fn tweak(self, tweak: Scalar<impl Secrecy, impl ZeroChoice>) -> Option<Self> {
let (new_agg_key, needs_negation) = g!(self.agg_key + tweak * G)
.normalize()
.non_zero()?
.into_point_with_even_y();
let mut new_tweak = s!(self.tweak + tweak).public();
new_tweak.conditional_negate(needs_negation);
let needs_negation = self.needs_negation ^ needs_negation;
Some(Self {
keys: self.keys,
coefs: self.coefs,
needs_negation,
tweak: new_tweak,
agg_key: new_agg_key,
})
}
}
impl<H: Digest<OutputSize = U32> + Clone, NG> MuSig<H, NG> {
/// Generates a new aggregated key from a list of individual keys.
///
/// Each party can be local (you know the secret key) or remote (you only know the public key).
///
/// ## Example
///
/// ```
/// use schnorr_fun::{
/// fun::{Point, Scalar},
/// musig::MuSig,
/// nonce::Deterministic,
/// Schnorr,
/// };
/// # let my_secret_key = Scalar::random(&mut rand::thread_rng());
/// # let their_public_key = Point::random(&mut rand::thread_rng());
/// use sha2::Sha256;
/// let musig = MuSig::<Sha256, Deterministic<Sha256>>::default();
/// let my_keypair = musig.new_keypair(my_secret_key);
/// let my_public_key = my_keypair.public_key();
/// // Note the keys have to come in the same order on the other side!
/// let agg_key = musig.new_agg_key(vec![their_public_key, my_public_key]);
/// ```
pub fn new_agg_key(&self, keys: Vec<Point>) -> AggKey<Normal> {
let coeff_hash = {
let L = self.pk_hash.clone().add(&keys[..]).finalize();
self.coeff_hash.clone().add(L.as_slice())
};
let mut second = None;
let coefs = keys
.iter()
.map(|key| {
// This is the logic for IsSecond from appendix B of the MuSig2 paper
if second.is_none() && key != &keys[0] {
second = Some(key);
}
if second != Some(key) {
Scalar::from_hash(coeff_hash.clone().add(key))
} else {
Scalar::one()
}
.public()
})
.collect::<Vec<_>>();
let agg_key = g!(&coefs .* &keys)
.non_zero().expect("computationally unreachable: linear combination of hash randomised points cannot add to zero");
AggKey {
keys,
coefs,
agg_key: agg_key.normalize(),
tweak: Scalar::zero(),
needs_negation: false,
}
}
}
impl<H, NG> MuSig<H, NG>
where
H: Digest<OutputSize = U32> + Clone,
NG: NonceGen,
{
/// Seed a random number generator to be used for MuSig nonces.
///
/// ** ⚠ WARNING ⚠**: This method is unstable and easy to use incorrectly. The seed it uses for
/// the Rng will change without warning between minor versions of this library.
///
/// Parameters:
///
/// - `agg_key`: the joint public key we are signing under. This can be an `XOnly` or `Normal`.
/// It will return the same nonce regardless.
/// - `secret`: you're secret key as part of `agg_key`. This **must be the secret key you are
/// going to sign with**. It cannot be an "untweaked" version of the signing key. It must be
/// exactly equal to the secret key you pass to [`sign`] (the MuSig specification requires this).
/// - `session_id`: a string of bytes that is **unique for each signing attempt**.
///
/// The application should decide upon a unique `session_id` per call to this function. If the
/// `NonceGen` of this MuSig instance is `Deterministic` then the `session_id` **must** be
/// unique per signing attempt -- even if the signing attempt fails to produce a signature you
/// must not reuse the session id, the resulting rng or anything derived from that rng again.
///
/// 💡 Before using this function write a short justification as to why your beleive your session
/// id will be unique per signing attempt. Perhaps include it as a comment next to the call.
/// Note **it must be unique even across signing attempts for the same or different messages**.
///
/// The rng returned can be used to create many nonces. For example, when signing a Bitcoin
/// transaction you may need to sign several inputs each with their own signature. It is
/// intended here that you call `seed_nonce_rng` once for the transaction and pull several nonces
/// out of the resulting rng.
///
/// [`sign`]: MuSig::sign
pub fn seed_nonce_rng<R: SeedableRng<Seed = [u8; 32]>>(
&self,
agg_key: &AggKey<impl Normalized>,
secret: &Scalar,
session_id: &[u8],
) -> R {
let sid_len = (session_id.len() as u64).to_be_bytes();
let pk_bytes = agg_key.agg_public_key().to_xonly_bytes();
let rng: R = secp256kfun::derive_nonce_rng!(
nonce_gen => self.nonce_gen(),
secret => &secret,
public => [pk_bytes, sid_len, session_id],
seedable_rng => R
);
rng
}
}
/// Marker type for indicating the [`SignSession`] is being used to create an ordinary Schnorr
/// signature.
#[derive(Debug, Clone, PartialEq)]
#[cfg_attr(
feature = "serde",
derive(crate::fun::serde::Deserialize, crate::fun::serde::Serialize),
serde(crate = "crate::fun::serde")
)]
#[cfg_attr(
feature = "bincode",
derive(crate::fun::bincode::Encode, crate::fun::bincode::Decode),
bincode(crate = "crate::fun::bincode")
)]
pub struct Ordinary;
/// Marks the [`SignSession`] as being used to create an adaptor (a.k.a. one-time encrypted)
/// signature.
#[derive(Debug, Clone, PartialEq)]
#[cfg_attr(
feature = "serde",
derive(crate::fun::serde::Deserialize, crate::fun::serde::Serialize),
serde(crate = "crate::fun::serde")
)]
#[cfg_attr(
feature = "bincode",
derive(crate::fun::bincode::Encode, crate::fun::bincode::Decode),
bincode(crate = "crate::fun::bincode")
)]
pub struct Adaptor {
y_needs_negation: bool,
}
/// A signing session.
///
/// Created by [`start_sign_session`] or [`start_encrypted_sign_session`].
/// The type parameter records whether you are trying to jointly generate a signature or an adaptor signature.
///
/// [`start_sign_session`]: MuSig::start_sign_session
/// [`start_encrypted_sign_session`]: MuSig::start_encrypted_sign_session
/// [`sign`]: MuSig::sign
#[derive(Debug, Clone, PartialEq)]
#[cfg_attr(
feature = "serde",
derive(crate::fun::serde::Deserialize, crate::fun::serde::Serialize),
serde(crate = "crate::fun::serde")
)]
#[cfg_attr(
feature = "bincode",
derive(crate::fun::bincode::Encode, crate::fun::bincode::Decode),
bincode(crate = "crate::fun::bincode")
)]
pub struct SignSession<T = Ordinary> {
b: Scalar<Public, Zero>,
c: Scalar<Public, Zero>,
public_nonces: Vec<Nonce>,
R: Point<EvenY>,
nonce_needs_negation: bool,
signing_type: T,
}
impl<H: Digest<OutputSize = U32> + Clone, NG> MuSig<H, NG> {
/// Start a signing session.
///
/// You must provide the public nonces for this signing session in the correct order.
///
/// ## Return Value
///
/// Returns `None` in the case that the `remote_nonces` have been (maliciously) selected to
/// cancel out your local nonces.
/// This is not a security issue -- we just can't continue the protocol if this happens.
///
/// # Panics
///
/// Panics if number of nonces does not align with the keys in `agg_key`.
pub fn start_sign_session(
&self,
agg_key: &AggKey<EvenY>,
nonces: Vec<Nonce>,
message: Message<'_, Public>,
) -> SignSession {
let (b, c, public_nonces, R, nonce_needs_negation) = self._start_sign_session(
agg_key,
nonces,
message,
&Point::<Normal, Public, _>::zero(),
);
SignSession {
b,
c,
public_nonces,
R,
nonce_needs_negation,
signing_type: Ordinary,
}
}
/// Start an encrypted signing session.
///
/// i.e. a session to produce an adaptor signature under `encryption_key`.
/// See [`adaptor`] for a more general description of adaptor signatures.
///
/// You must provide the public nonces (where your public portions must be
/// shared with the other signer(s)).
///
/// ## Return Value
///
/// Returns `None` in the case that the `remote_nonces` have been (maliciously) selected to
/// cancel out your local nonces.
/// This is not a security issue -- we just can't continue the protocol if this happens.
///
/// # Panics
///
/// Panics if number of local or remote nonces passed in does not align with the keys in
/// `agg_key`.
///
/// [`adaptor`]: crate::adaptor
pub fn start_encrypted_sign_session(
&self,
agg_key: &AggKey<EvenY>,
nonces: Vec<Nonce>,
message: Message<'_, Public>,
encryption_key: &Point<impl PointType, impl Secrecy, impl ZeroChoice>,
) -> Option<SignSession<Adaptor>> {
let (b, c, public_nonces, R, nonce_needs_negation) =
self._start_sign_session(agg_key, nonces, message, encryption_key);
Some(SignSession {
b,
c,
public_nonces,
R,
nonce_needs_negation,
signing_type: Adaptor {
y_needs_negation: nonce_needs_negation,
},
})
}
#[allow(clippy::type_complexity)]
fn _start_sign_session(
&self,
agg_key: &AggKey<EvenY>,
nonces: Vec<Nonce>,
message: Message<'_, Public>,
encryption_key: &Point<impl PointType, impl Secrecy, impl ZeroChoice>,
) -> (
Scalar<Public, Zero>,
Scalar<Public, Zero>,
Vec<Nonce>,
Point<EvenY>,
bool,
) {
let mut Rs = nonces;
let agg_Rs = Rs.iter().fold([Point::zero(); 2], |acc, nonce| {
[g!(acc[0] + nonce.0[0]), g!(acc[1] + nonce.0[1])]
});
let agg_Rs = Nonce::<Zero>([
g!(agg_Rs[0] + encryption_key).normalize(),
agg_Rs[1].normalize(),
]);
let b = {
let H = self.nonce_coeff_hash.clone();
Scalar::from_hash(
H.add(agg_Rs.to_bytes())
.add(agg_key.agg_public_key())
.add(message),
)
}
.public()
.mark_zero();
let (R, r_needs_negation) = g!(agg_Rs.0[0] + b * agg_Rs.0[1])
.normalize()
.non_zero()
.unwrap_or(Point::generator())
.into_point_with_even_y();
for R_i in &mut Rs {
R_i.conditional_negate(r_needs_negation);
}
let c = self
.schnorr
.challenge(&R, &agg_key.agg_public_key(), message);
(b, c, Rs, R, r_needs_negation)
}
/// Generates a partial signature (or partial encrypted signature depending on `T`) for the local_secret_nonce.
pub fn sign<T>(
&self,
agg_key: &AggKey<EvenY>,
session: &SignSession<T>,
my_index: usize,
keypair: &KeyPair,
local_secret_nonce: NonceKeyPair,
) -> Scalar<Public, Zero> {
assert_eq!(
keypair.public_key(),
agg_key.keys().nth(my_index).unwrap(),
"key at index {my_index} didn't match",
);
let c = session.c;
let b = session.b;
let x_i = keypair.secret_key();
let mut a = agg_key.coefs[my_index];
a.conditional_negate(agg_key.needs_negation);
let [mut r1, mut r2] = local_secret_nonce.secret;
r1.conditional_negate(session.nonce_needs_negation);
r2.conditional_negate(session.nonce_needs_negation);
s!(c * a * x_i + r1 + b * r2).public()
}
#[must_use]
/// Verifies a partial signature (or partial encrypted signature depending on `T`).
///
/// You must provide the `index` of the party (the index of the key in `agg_key`).
///
/// # Panics
///
/// Panics when `index` is equal to or greater than the number of keys in the agg_key.
pub fn verify_partial_signature<T>(
&self,
agg_key: &AggKey<EvenY>,
session: &SignSession<T>,
index: usize,
partial_sig: Scalar<Public, Zero>,
) -> bool {
let c = session.c;
let b = session.b;
let s_i = &partial_sig;
let a = agg_key.coefs[index];
let X_i = agg_key
.keys()
.nth(index)
.unwrap()
.conditional_negate(agg_key.needs_negation);
let [R1, R2] = &session.public_nonces[index].0;
g!((c * a) * X_i + R1 + b * R2 - s_i * G).is_zero()
}
/// Combines all the partial signatures into a single `Signature`.
///
/// Note this does not check the validity of any of the partial signatures. You should either check
/// each one using [`verify_partial_signature`] or use [`verify`] on the returned `Signature` to check validity.
///
/// [`verify`]: crate::Schnorr::verify
/// [`verify_partial_signature`]: Self::verify_partial_signature
pub fn combine_partial_signatures(
&self,
agg_key: &AggKey<EvenY>,
session: &SignSession<Ordinary>,
partial_sigs: impl IntoIterator<Item = Scalar<Public, Zero>>,
) -> Signature {
let (R, s) = self._combine_partial_signatures(agg_key, session, partial_sigs);
Signature { R, s }
}
/// Combines all the partial encrypted signatures into one encrypted signature.
///
/// Note this does not check the validity of any of the partial signatures. You should either check
/// each one using [`verify_partial_signature`] or use [`verify_encrypted_signature`] on the returned `Signature` to check validity.
///
/// [`verify_encrypted_signature`]: crate::adaptor::Adaptor::verify_encrypted_signature
/// [`verify_partial_signature`]: Self::verify_partial_signature
pub fn combine_partial_encrypted_signatures(
&self,
agg_key: &AggKey<EvenY>,
session: &SignSession<Adaptor>,
partial_encrypted_sigs: impl IntoIterator<Item = Scalar<Public, Zero>>,
) -> EncryptedSignature {
let (R, s_hat) = self._combine_partial_signatures(agg_key, session, partial_encrypted_sigs);
EncryptedSignature {
R,
s_hat,
needs_negation: session.signing_type.y_needs_negation,
}
}
fn _combine_partial_signatures<T>(
&self,
agg_key: &AggKey<EvenY>,
session: &SignSession<T>,
partial_sigs: impl IntoIterator<Item = Scalar<Public, Zero>>,
) -> (Point<EvenY>, Scalar<Public, Zero>) {
let sum_s = partial_sigs
.into_iter()
.reduce(|acc, s| s!(acc + s).public())
.unwrap_or(Scalar::zero());
let s = s!(sum_s + agg_key.tweak * session.c).public();
(session.R, s)
}
}
/// Constructor for a MuSig instance using deterministic nonce generation.
///
/// If you use deterministic nonce generation you will have to provide a unique session id to every
/// signing session. The advantage is that you will be able to regenerate the same nonces at a later
/// point from [`MuSig::seed_nonce_rng`].
///
/// ```
/// use schnorr_fun::musig;
/// let musig = musig::new_with_deterministic_nonces::<sha2::Sha256>();
/// ```
pub fn new_with_deterministic_nonces<H>() -> MuSig<H, nonce::Deterministic<H>>
where
H: Tag + Digest<OutputSize = U32> + Default + Clone,
{
MuSig::default()
}
/// Constructor for a MuSig instance using synthetic nonce generation.
///
/// Sythetic nonce generation mixes in external randomness into nonce generation which means you
/// don't need a unique session id for each signing session to guarantee security. The disadvantage
/// is that you may have to store and recall somehow the nonces generated from
/// [`MuSig::seed_nonce_rng`].
///
/// ```
/// use schnorr_fun::musig;
/// let musig = musig::new_with_synthetic_nonces::<sha2::Sha256, rand::rngs::ThreadRng>();
/// ```
pub fn new_with_synthetic_nonces<H, R>() -> MuSig<H, nonce::Synthetic<H, nonce::GlobalRng<R>>>
where
H: Tag + Digest<OutputSize = U32> + Default + Clone,
R: RngCore + Default + Clone,
{
MuSig::default()
}
/// Create a MuSig instance which does not handle nonce generation.
///
/// You can still sign with this instance but you you will have to generate nonces in your own way.
pub fn new_without_nonce_generation<H>() -> MuSig<H, NoNonces>
where
H: Tag + Digest<OutputSize = U32> + Default,
{
MuSig::default()
}
#[cfg(test)]
mod test {
use crate::adaptor::Adaptor;
use super::*;
use rand_chacha::ChaCha20Rng;
use secp256kfun::proptest::{option, prelude::*};
use sha2::Sha256;
proptest! {
#[test]
fn proptest_sign_verify(sk1 in any::<Scalar>(),
sk2 in any::<Scalar>(),
sk3 in any::<Scalar>(),
pre_tweak1 in option::of(any::<Scalar<Public, Zero>>()),
pre_tweak2 in option::of(any::<Scalar<Public, Zero>>()),
tweak1 in option::of(any::<Scalar<Public, Zero>>()),
tweak2 in option::of(any::<Scalar<Public, Zero>>()),
) {
let schnorr = Schnorr::<Sha256, nonce::Deterministic<Sha256>>::default();
let musig = MuSig::new(schnorr);
let keypair1 = musig
.new_keypair(sk1);
let keypair2 = musig
.new_keypair(sk2);
let keypair3 = musig
.new_keypair(sk3);
let mut agg_key1 = musig.new_agg_key(vec![
keypair1.public_key(),
keypair2.public_key(),
keypair3.public_key(),
]);
let mut agg_key2 = musig.new_agg_key(vec![
keypair1.public_key(),
keypair2.public_key(),
keypair3.public_key(),
]);
let mut agg_key3 = musig.new_agg_key(vec![
keypair1.public_key(),
keypair2.public_key(),
keypair3.public_key(),
]);
for tweak in [pre_tweak1, pre_tweak2].into_iter().flatten() {
agg_key1 = agg_key1.tweak(tweak).unwrap();
agg_key2 = agg_key2.tweak(tweak).unwrap();
agg_key3 = agg_key3.tweak(tweak).unwrap();
}
let mut agg_key1 = agg_key1.into_xonly_key();
let mut agg_key2 = agg_key2.into_xonly_key();
let mut agg_key3 = agg_key3.into_xonly_key();
for tweak in [tweak1, tweak2].into_iter().flatten() {
agg_key1 = agg_key1.tweak(tweak).unwrap();
agg_key2 = agg_key2.tweak(tweak).unwrap();
agg_key3 = agg_key3.tweak(tweak).unwrap();
}
assert_eq!(agg_key1.agg_public_key(), agg_key2.agg_public_key());
assert_eq!(agg_key1.agg_public_key(), agg_key3.agg_public_key());
let message =
Message::<Public>::plain("test", b"Chancellor on brink of second bailout for banks");
let session_id = message.bytes.into();
let mut nonce_rng: ChaCha20Rng = musig.seed_nonce_rng(&agg_key1, keypair1.secret_key(), session_id);
let p1_nonce = musig.gen_nonce(&mut nonce_rng);
let p2_nonce = musig.gen_nonce(&mut nonce_rng);
let p3_nonce = musig.gen_nonce(&mut nonce_rng);
let nonces = vec![p1_nonce.public, p2_nonce.public, p3_nonce.public];
let p1_session = musig
.start_sign_session(
&agg_key1,
nonces.clone(),
message,
);
let p2_session = musig
.start_sign_session(
&agg_key2,
nonces.clone(),
message,
);
let p3_session = musig
.start_sign_session(
&agg_key3,
nonces,
message,
);
let p1_sig = musig.sign(&agg_key1, &p1_session, 0, &keypair1, p1_nonce);
assert!(musig.verify_partial_signature(&agg_key1, &p1_session, 0, p1_sig));
assert_eq!(p1_session, p2_session);
assert!(musig.verify_partial_signature(&agg_key1, &p2_session, 0, p1_sig));
assert!(musig.verify_partial_signature(&agg_key1, &p3_session, 0, p1_sig));
let p2_sig = musig.sign(&agg_key1, &p2_session, 1, &keypair2, p2_nonce);
assert!(musig.verify_partial_signature(&agg_key1, &p1_session, 1, p2_sig));
let p3_sig = musig.sign(&agg_key1, &p3_session, 2, &keypair3, p3_nonce);
assert!(musig.verify_partial_signature(&agg_key1, &p1_session, 2, p3_sig));
let partial_sigs = [p1_sig, p2_sig, p3_sig];
let sig_p1 = musig.combine_partial_signatures(&agg_key1, &p1_session, partial_sigs);
let sig_p2 = musig.combine_partial_signatures(&agg_key1, &p2_session, partial_sigs);
let sig_p3 = musig.combine_partial_signatures(&agg_key1, &p3_session, partial_sigs);
assert_eq!(sig_p1, sig_p2);
assert_eq!(sig_p1, sig_p3);
assert!(musig
.schnorr
.verify(&agg_key1.agg_public_key(), message, &sig_p1));
assert!(musig
.schnorr
.verify(&agg_key1.agg_public_key(), message, &sig_p2));
assert!(musig
.schnorr
.verify(&agg_key1.agg_public_key(), message, &sig_p3));
}
#[test]
fn test_musig_adaptor(
sk1 in any::<Scalar>(),
sk2 in any::<Scalar>(),
sk3 in any::<Scalar>(),
y in any::<Scalar>()
) {
let schnorr = Schnorr::<Sha256, nonce::Deterministic<Sha256>>::default();
let musig = MuSig::new(schnorr);
let keypair1 = musig
.new_keypair(sk1);
let keypair2 = musig
.new_keypair(sk2);
let keypair3 = musig
.new_keypair(sk3);
let encryption_key = musig.schnorr.encryption_key_for(&y);
let agg_key1 = musig.new_agg_key(vec![
keypair1.public_key(),
keypair2.public_key(),
keypair3.public_key(),
]).into_xonly_key();
let agg_key2 = musig.new_agg_key(vec![
keypair1.public_key(),
keypair2.public_key(),
keypair3.public_key(),
]).into_xonly_key();
let agg_key3 = musig.new_agg_key(vec![
keypair1.public_key(),
keypair2.public_key(),
keypair3.public_key(),
]).into_xonly_key();
let message =
Message::<Public>::plain("test", b"Chancellor on brink of second bailout for banks");
let session_id = message.bytes.into();
let mut nonce_rng: ChaCha20Rng = musig.seed_nonce_rng(&agg_key1, keypair1.secret_key(), session_id);
let p1_nonce = musig.gen_nonce(&mut nonce_rng);
let p2_nonce = musig.gen_nonce(&mut nonce_rng);
let p3_nonce = musig.gen_nonce(&mut nonce_rng);
let nonces = vec![p1_nonce.public, p2_nonce.public, p3_nonce.public];
let p1_session = musig
.start_encrypted_sign_session(
&agg_key1,
nonces.clone(),
message,
&encryption_key
)
.unwrap();
let p2_session = musig
.start_encrypted_sign_session(
&agg_key2,
nonces.clone(),
message,
&encryption_key
)
.unwrap();
let p3_session = musig
.start_encrypted_sign_session(
&agg_key3,
nonces,
message,
&encryption_key
)
.unwrap();
let p1_sig = musig.sign(&agg_key1, &p1_session, 0, &keypair1, p1_nonce);
let p2_sig = musig.sign(&agg_key1, &p2_session, 1, &keypair2, p2_nonce);
let p3_sig = musig.sign(&agg_key1, &p3_session, 2, &keypair3, p3_nonce);
assert!(musig.verify_partial_signature(&agg_key2, &p2_session, 0, p1_sig));
assert!(musig.verify_partial_signature(&agg_key1, &p1_session, 0, p1_sig));
let partial_sigs = vec![p1_sig, p2_sig, p3_sig];
let combined_sig_p1 = musig.combine_partial_encrypted_signatures(&agg_key1, &p1_session, partial_sigs.clone());
let combined_sig_p2 = musig.combine_partial_encrypted_signatures(&agg_key2, &p2_session, partial_sigs.clone());
let combined_sig_p3 = musig.combine_partial_encrypted_signatures(&agg_key3, &p3_session, partial_sigs);
assert_eq!(combined_sig_p1, combined_sig_p2);
assert_eq!(combined_sig_p1, combined_sig_p3);
assert!(musig
.schnorr
.verify_encrypted_signature(&agg_key1.agg_public_key(), &encryption_key, message, &combined_sig_p1));
assert!(musig
.schnorr
.verify_encrypted_signature(&agg_key2.agg_public_key(), &encryption_key, message, &combined_sig_p2));
assert!(musig
.schnorr
.verify_encrypted_signature(&agg_key2.agg_public_key(), &encryption_key, message, &combined_sig_p3));
}
}
}