pub use secp256k1zkp::{ContextFlag, Message, Secp256k1, Signature}; pub use secp256k1zkp::aggsig; pub use secp256k1zkp::ecdh::SharedSecret; pub use secp256k1zkp::pedersen::{Commitment, RangeProof}; pub use secp256k1zkp::key::{PublicKey, SecretKey, ZERO_KEY}; pub use secp256k1zkp::constants::{AGG_SIGNATURE_SIZE, COMPRESSED_PUBLIC_KEY_SIZE, MAX_PROOF_SIZE, PEDERSEN_COMMITMENT_SIZE, SECRET_KEY_SIZE}; use crate::error::{Error, ErrorKind, Result}; use blake2::blake2b::Blake2b; use byteorder::{BigEndian, ByteOrder}; use grin_core::ser::{self, Readable, Reader, Writeable, Writer}; use secp256k1zkp::rand::thread_rng; /// A generalized Schnorr signature with a pedersen commitment value & blinding factors as the keys pub struct ComSignature { pub_nonce: Commitment, s: SecretKey, t: SecretKey, } impl ComSignature { pub fn new(pub_nonce: &Commitment, s: &SecretKey, t: &SecretKey) -> ComSignature { ComSignature { pub_nonce: pub_nonce.to_owned(), s: s.to_owned(), t: t.to_owned(), } } #[allow(dead_code)] pub fn sign(amount: u64, blind: &SecretKey, msg: &Vec) -> Result { let secp = Secp256k1::with_caps(ContextFlag::Commit); let mut amt_bytes = [0; 32]; BigEndian::write_u64(&mut amt_bytes[24..32], amount); let k_amt = SecretKey::from_slice(&secp, &amt_bytes)?; let k_1 = SecretKey::new(&secp, &mut thread_rng()); let k_2 = SecretKey::new(&secp, &mut thread_rng()); let commitment = secp.commit(amount, blind.clone())?; let nonce_commitment = secp.commit_blind(k_1.clone(), k_2.clone())?; let e = ComSignature::calc_challenge(&secp, &commitment, &nonce_commitment, &msg)?; // s = k_1 + (e * amount) let mut s = k_amt.clone(); s.mul_assign(&secp, &e)?; s.add_assign(&secp, &k_1)?; // t = k_2 + (e * blind) let mut t = blind.clone(); t.mul_assign(&secp, &e)?; t.add_assign(&secp, &k_2)?; Ok(ComSignature::new(&nonce_commitment, &s, &t)) } #[allow(non_snake_case)] pub fn verify(&self, commit: &Commitment, msg: &Vec) -> Result<()> { let secp = Secp256k1::with_caps(ContextFlag::Commit); let S1 = secp.commit_blind(self.s.clone(), self.t.clone())?; let mut Ce = commit.to_pubkey(&secp)?; let e = ComSignature::calc_challenge(&secp, &commit, &self.pub_nonce, &msg)?; Ce.mul_assign(&secp, &e)?; let commits = vec![Commitment::from_pubkey(&secp, &Ce)?, self.pub_nonce.clone()]; let S2 = secp.commit_sum(commits, Vec::new())?; if S1 != S2 { return Err(Error::new(ErrorKind::InvalidSigError)); } Ok(()) } fn calc_challenge(secp: &Secp256k1, commit: &Commitment, nonce_commit: &Commitment, msg: &Vec) -> Result { let mut challenge_hasher = Blake2b::new(32); challenge_hasher.update(&commit.0); challenge_hasher.update(&nonce_commit.0); challenge_hasher.update(msg); let mut challenge = [0; 32]; challenge.copy_from_slice(challenge_hasher.finalize().as_bytes()); Ok(SecretKey::from_slice(&secp, &challenge)?) } } /// Serializes a ComSignature to and from hex pub mod comsig_serde { use super::ComSignature; use grin_core::ser::{self, ProtocolVersion}; use serde::{Deserialize, Serializer}; use grin_util::ToHex; /// Serializes a ComSignature as a hex string pub fn serialize(comsig: &ComSignature, serializer: S) -> Result where S: Serializer, { use serde::ser::Error; let bytes = ser::ser_vec(&comsig, ProtocolVersion::local()).map_err(Error::custom)?; serializer.serialize_str(&bytes.to_hex()) } /// Creates a ComSignature from a hex string pub fn deserialize<'de, D>(deserializer: D) -> std::result::Result where D: serde::Deserializer<'de>, { use serde::de::Error; let bytes = String::deserialize(deserializer) .and_then(|string| grin_util::from_hex(&string).map_err(Error::custom))?; let sig: ComSignature = grin_core::ser::deserialize_default(&mut &bytes[..]) .map_err(Error::custom)?; Ok(sig) } } #[allow(non_snake_case)] impl Readable for ComSignature { fn read(reader: &mut R) -> std::result::Result { let R = Commitment::read(reader)?; let s = read_secret_key(reader)?; let t = read_secret_key(reader)?; Ok(ComSignature::new(&R, &s, &t)) } } impl Writeable for ComSignature { fn write(&self, writer: &mut W) -> std::result::Result<(), ser::Error> { writer.write_fixed_bytes(self.pub_nonce.0)?; writer.write_fixed_bytes(self.s.0)?; writer.write_fixed_bytes(self.t.0)?; Ok(()) } } /// Generate a random SecretKey. pub fn random_secret() -> SecretKey { let secp = Secp256k1::new(); SecretKey::new(&secp, &mut thread_rng()) } /// Deserialize a SecretKey from a Reader pub fn read_secret_key(reader: &mut R) -> std::result::Result { let buf = reader.read_fixed_bytes(SECRET_KEY_SIZE)?; let secp = Secp256k1::with_caps(ContextFlag::None); let pk = SecretKey::from_slice(&secp, &buf).map_err(|_| ser::Error::CorruptedData)?; Ok(pk) } /// Build a Pedersen Commitment using the provided value and blinding factor pub fn commit(value: u64, blind: &SecretKey) -> Result { let secp = Secp256k1::with_caps(ContextFlag::Commit); let commit = secp.commit(value, blind.clone())?; Ok(commit) } /// Add a blinding factor to an existing Commitment pub fn add_excess(commitment: &Commitment, excess: &SecretKey) -> Result { let secp = Secp256k1::with_caps(ContextFlag::Commit); let excess_commit : Commitment = secp.commit(0, excess.clone())?; let commits = vec![commitment.clone(), excess_commit.clone()]; let sum = secp.commit_sum(commits, Vec::new())?; Ok(sum) } /// Subtracts a value (v*H) from an existing commitment pub fn sub_value(commitment: &Commitment, value: u64) -> Result { let secp = Secp256k1::with_caps(ContextFlag::Commit); let neg_commit : Commitment = secp.commit(value, ZERO_KEY)?; let sum = secp.commit_sum(vec![commitment.clone()], vec![neg_commit.clone()])?; Ok(sum) } /// Signs the message with the provided SecretKey pub fn sign(sk: &SecretKey, msg: &Message) -> Result { let secp = Secp256k1::with_caps(ContextFlag::Full); let pubkey = PublicKey::from_secret_key(&secp, &sk)?; let sig = aggsig::sign_single(&secp, &msg, &sk, None, None, None, Some(&pubkey), None)?; Ok(sig) } #[cfg(test)] mod tests { use super::{ComSignature, ContextFlag, Secp256k1, SecretKey}; use crate::error::Result; use secp256k1zkp::rand::{RngCore, thread_rng}; use rand::Rng; /// Test signing and verification of ComSignatures #[test] fn verify_comsig() -> Result<()> { let secp = Secp256k1::with_caps(ContextFlag::Commit); let amount = thread_rng().next_u64(); let blind = SecretKey::new(&secp, &mut thread_rng()); let msg: [u8; 16] = rand::thread_rng().gen(); let comsig = ComSignature::sign(amount, &blind, &msg.to_vec())?; let commit = secp.commit(amount, blind.clone())?; assert!(comsig.verify(&commit, &msg.to_vec()).is_ok()); let wrong_msg: [u8; 16] = rand::thread_rng().gen(); assert!(comsig.verify(&commit, &wrong_msg.to_vec()).is_err()); let wrong_commit = secp.commit(amount, SecretKey::new(&secp, &mut thread_rng()))?; assert!(comsig.verify(&wrong_commit, &msg.to_vec()).is_err()); Ok(()) } }