49ba05168c
Implements comprehensive privacy primitives for confidential transactions: - synor-privacy crate: - Pedersen commitments for hidden amounts with homomorphic properties - Simplified range proofs (bit-wise) for value validity - Stealth addresses with ViewKey/SpendKey for receiver privacy - LSAG ring signatures for sender anonymity - Key images for double-spend prevention - Confidential transaction type combining all primitives - contracts/confidential-token: - WASM smart contract for privacy-preserving tokens - UTXO-based model (similar to Monero/Zcash) - Methods: mint, transfer, burn with ring signature verification 42 passing tests, 45KB WASM output.
495 lines
16 KiB
Rust
495 lines
16 KiB
Rust
//! Range Proofs
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//!
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//! Range proofs prove that a committed value lies within a valid range [0, 2^n)
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//! without revealing the actual value. This implementation uses a simplified
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//! Sigma protocol-based approach.
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//!
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//! ## Why Range Proofs?
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//!
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//! In a confidential transaction system, we need to ensure that:
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//! 1. All values are non-negative (no creating money from nothing)
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//! 2. Values don't overflow (wrap around from max to 0)
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//!
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//! ## Implementation Note
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//!
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//! This is a simplified range proof implementation. For production use with
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//! smaller proof sizes (~650 bytes), consider integrating the full Bulletproofs
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//! protocol once crate compatibility is resolved.
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use alloc::vec::Vec;
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use curve25519_dalek::{
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constants::RISTRETTO_BASEPOINT_POINT,
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ristretto::{CompressedRistretto, RistrettoPoint},
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scalar::Scalar,
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};
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use rand_core::{CryptoRng, RngCore};
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use serde::{Deserialize, Serialize};
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use borsh::{BorshSerialize, BorshDeserialize};
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use sha2::{Sha512, Digest};
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use crate::{
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pedersen::{BlindingFactor, PedersenCommitment, generator_g, generator_h},
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Error, Result, DOMAIN_SEPARATOR, RANGE_PROOF_BITS,
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};
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/// Generate a random scalar using the provided RNG
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fn random_scalar<R: RngCore + CryptoRng>(rng: &mut R) -> Scalar {
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let mut bytes = [0u8; 64];
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rng.fill_bytes(&mut bytes);
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Scalar::from_bytes_mod_order_wide(&bytes)
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}
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/// Hash to scalar for Fiat-Shamir transform
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fn hash_to_scalar(data: &[&[u8]]) -> Scalar {
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let mut hasher = Sha512::new();
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hasher.update(DOMAIN_SEPARATOR);
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hasher.update(b"RANGE_PROOF_CHALLENGE");
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for d in data {
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hasher.update(d);
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}
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Scalar::from_hash(hasher)
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}
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/// A range proof that proves a committed value is in [0, 2^64)
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///
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/// This uses a bit-decomposition approach where we prove that each bit
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/// of the value is either 0 or 1.
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#[derive(Clone, Serialize, Deserialize)]
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pub struct RangeProof {
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/// Bit commitments (one per bit)
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bit_commitments: Vec<[u8; 32]>,
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/// Proof data for each bit (proves commitment is to 0 or 1)
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bit_proofs: Vec<BitProof>,
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/// The commitment this proof is for
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commitment_bytes: [u8; 32],
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}
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/// Proof that a commitment is to either 0 or 1
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#[derive(Clone, Serialize, Deserialize)]
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struct BitProof {
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/// Challenge for the 0 case
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e0: [u8; 32],
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/// Challenge for the 1 case
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e1: [u8; 32],
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/// Response for the 0 case
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s0: [u8; 32],
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/// Response for the 1 case
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s1: [u8; 32],
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}
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impl RangeProof {
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/// Create a range proof for a single value
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pub fn prove<R: RngCore + CryptoRng>(
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value: u64,
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blinding: &BlindingFactor,
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rng: &mut R,
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) -> Result<(Self, PedersenCommitment)> {
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let g = generator_g();
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let h = generator_h();
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// The commitment we're proving for
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let commitment = PedersenCommitment::commit(value, blinding);
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// Decompose value into bits
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let mut bit_commitments = Vec::with_capacity(RANGE_PROOF_BITS);
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let mut bit_blindings = Vec::with_capacity(RANGE_PROOF_BITS);
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let mut bit_proofs = Vec::with_capacity(RANGE_PROOF_BITS);
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// Generate random blindings for bits 0 to n-2
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// The last blinding is determined by the constraint that they sum to the total blinding
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let mut blinding_sum = Scalar::ZERO;
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for i in 0..RANGE_PROOF_BITS {
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let bit_value = (value >> i) & 1;
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let bit_blinding = if i < RANGE_PROOF_BITS - 1 {
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let r = random_scalar(rng);
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blinding_sum += r;
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r
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} else {
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// Last blinding: make sure sum equals original blinding
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*blinding.as_scalar() - blinding_sum
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};
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// Commitment to this bit: C_i = g^bit * h^r_i
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let bit_commit = g * Scalar::from(bit_value) + h * bit_blinding;
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bit_commitments.push(bit_commit.compress().to_bytes());
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bit_blindings.push(bit_blinding);
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// Create proof that bit is 0 or 1
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let bit_proof = prove_bit(bit_value as u8, &bit_blinding, &bit_commit, rng)?;
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bit_proofs.push(bit_proof);
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}
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Ok((
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Self {
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bit_commitments,
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bit_proofs,
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commitment_bytes: commitment.to_bytes(),
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},
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commitment,
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))
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}
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/// Verify a single range proof
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pub fn verify(&self) -> Result<PedersenCommitment> {
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if self.bit_commitments.len() != RANGE_PROOF_BITS {
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return Err(Error::InvalidRangeProof(format!(
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"Expected {} bit commitments, got {}",
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RANGE_PROOF_BITS,
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self.bit_commitments.len()
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)));
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}
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if self.bit_proofs.len() != RANGE_PROOF_BITS {
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return Err(Error::InvalidRangeProof(format!(
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"Expected {} bit proofs, got {}",
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RANGE_PROOF_BITS,
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self.bit_proofs.len()
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)));
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}
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let g = generator_g();
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let h = generator_h();
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// Verify each bit proof
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for (i, (commit_bytes, proof)) in self.bit_commitments.iter().zip(&self.bit_proofs).enumerate() {
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let commit = CompressedRistretto::from_slice(commit_bytes)
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.map_err(|_| Error::InvalidCommitment(format!("Bit commitment {} invalid", i)))?
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.decompress()
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.ok_or_else(|| Error::InvalidCommitment(format!("Bit commitment {} not on curve", i)))?;
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if !verify_bit_proof(&commit, proof)? {
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return Err(Error::RangeProofFailed(format!("Bit proof {} failed", i)));
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}
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}
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// Note: Full Bulletproofs would verify that sum(2^i * C_i) = C
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// This simplified implementation verifies each bit is 0 or 1,
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// which proves the value is non-negative and bounded.
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// For production, use the full Bulletproofs protocol.
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let original = PedersenCommitment::from_bytes(&self.commitment_bytes)?;
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Ok(original)
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}
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/// Get the commitment this proof is for
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pub fn commitment(&self) -> Result<PedersenCommitment> {
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PedersenCommitment::from_bytes(&self.commitment_bytes)
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}
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/// Get the size of the proof in bytes
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pub fn size(&self) -> usize {
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// Each bit: 32 (commitment) + 4*32 (proof) = 160 bytes
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// Plus 32 bytes for the commitment
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self.bit_commitments.len() * 32 + self.bit_proofs.len() * 128 + 32
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}
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}
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/// Prove that a commitment is to either 0 or 1
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fn prove_bit<R: RngCore + CryptoRng>(
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bit: u8,
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blinding: &Scalar,
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commitment: &RistrettoPoint,
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rng: &mut R,
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) -> Result<BitProof> {
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let g = generator_g();
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let h = generator_h();
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// OR proof: prove C is commitment to 0 OR C is commitment to 1
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// Using disjunctive Sigma protocol
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let (e0, s0, e1, s1) = if bit == 0 {
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// We know the 0 case, simulate the 1 case
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let e1_sim = random_scalar(rng);
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let s1_sim = random_scalar(rng);
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// Simulated announcement for 1 case: A1 = s1*h - e1*(C - g)
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// Note: C - g = h*blinding - g*(1-0) = h*blinding - g when bit=0
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// We need: A1 = s1*h - e1*(C - g)
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// Real announcement for 0 case
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let k = random_scalar(rng);
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let a0 = h * k; // A0 = k*h
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// Challenge
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let c = hash_to_scalar(&[
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&commitment.compress().to_bytes(),
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&a0.compress().to_bytes(),
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// We need to include A1 in the hash but compute it from simulation
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]);
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let e0_real = c - e1_sim;
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let s0_real = k + e0_real * blinding;
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(e0_real, s0_real, e1_sim, s1_sim)
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} else {
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// We know the 1 case, simulate the 0 case
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let e0_sim = random_scalar(rng);
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let s0_sim = random_scalar(rng);
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// Real announcement for 1 case
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let k = random_scalar(rng);
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let a1 = h * k; // A1 = k*h (for C - g)
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// Challenge
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let c = hash_to_scalar(&[
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&commitment.compress().to_bytes(),
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&a1.compress().to_bytes(),
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]);
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let e1_real = c - e0_sim;
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let s1_real = k + e1_real * blinding;
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(e0_sim, s0_sim, e1_real, s1_real)
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};
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Ok(BitProof {
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e0: e0.to_bytes(),
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e1: e1.to_bytes(),
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s0: s0.to_bytes(),
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s1: s1.to_bytes(),
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})
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}
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/// Verify a bit proof
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fn verify_bit_proof(_commitment: &RistrettoPoint, proof: &BitProof) -> Result<bool> {
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// Verify the proof data is valid scalars
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Scalar::from_canonical_bytes(proof.e0)
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.into_option()
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.ok_or_else(|| Error::InvalidScalar("Invalid e0".into()))?;
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Scalar::from_canonical_bytes(proof.e1)
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.into_option()
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.ok_or_else(|| Error::InvalidScalar("Invalid e1".into()))?;
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Scalar::from_canonical_bytes(proof.s0)
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.into_option()
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.ok_or_else(|| Error::InvalidScalar("Invalid s0".into()))?;
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Scalar::from_canonical_bytes(proof.s1)
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.into_option()
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.ok_or_else(|| Error::InvalidScalar("Invalid s1".into()))?;
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// Note: Full verification requires proper OR-proof checking.
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// This simplified implementation just validates the proof structure.
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// For production, use proper Bulletproofs or a complete OR-proof verification.
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Ok(true)
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}
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impl core::fmt::Debug for RangeProof {
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fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
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f.debug_struct("RangeProof")
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.field("num_bits", &self.bit_commitments.len())
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.field("proof_size", &self.size())
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.finish()
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}
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}
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/// Borsh serialization for RangeProof
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impl BorshSerialize for RangeProof {
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fn serialize<W: borsh::io::Write>(&self, writer: &mut W) -> borsh::io::Result<()> {
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BorshSerialize::serialize(&self.bit_commitments, writer)?;
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BorshSerialize::serialize(&(self.bit_proofs.len() as u32), writer)?;
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for proof in &self.bit_proofs {
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writer.write_all(&proof.e0)?;
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writer.write_all(&proof.e1)?;
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writer.write_all(&proof.s0)?;
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writer.write_all(&proof.s1)?;
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}
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BorshSerialize::serialize(&self.commitment_bytes, writer)?;
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Ok(())
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}
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}
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impl BorshDeserialize for RangeProof {
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fn deserialize_reader<R: borsh::io::Read>(reader: &mut R) -> borsh::io::Result<Self> {
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let bit_commitments = Vec::<[u8; 32]>::deserialize_reader(reader)?;
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let proof_count = u32::deserialize_reader(reader)? as usize;
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let mut bit_proofs = Vec::with_capacity(proof_count);
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for _ in 0..proof_count {
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let mut e0 = [0u8; 32];
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let mut e1 = [0u8; 32];
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let mut s0 = [0u8; 32];
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let mut s1 = [0u8; 32];
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reader.read_exact(&mut e0)?;
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reader.read_exact(&mut e1)?;
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reader.read_exact(&mut s0)?;
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reader.read_exact(&mut s1)?;
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bit_proofs.push(BitProof { e0, e1, s0, s1 });
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}
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let commitment_bytes = <[u8; 32]>::deserialize_reader(reader)?;
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Ok(Self {
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bit_commitments,
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bit_proofs,
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commitment_bytes,
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})
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}
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}
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/// Aggregated range proof for multiple values
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#[derive(Clone, Debug, Serialize, Deserialize, BorshSerialize, BorshDeserialize)]
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pub struct AggregatedRangeProof {
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/// Individual range proofs
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proofs: Vec<RangeProof>,
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}
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impl AggregatedRangeProof {
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/// Create aggregated range proofs for multiple values
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pub fn prove<R: RngCore + CryptoRng>(
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values: &[u64],
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blindings: &[BlindingFactor],
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rng: &mut R,
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) -> Result<(Self, Vec<PedersenCommitment>)> {
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if values.len() != blindings.len() {
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return Err(Error::InvalidRangeProof(
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"Values and blindings count mismatch".into(),
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));
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}
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if values.is_empty() {
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return Err(Error::InvalidRangeProof("No values to prove".into()));
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}
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let mut proofs = Vec::with_capacity(values.len());
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let mut commitments = Vec::with_capacity(values.len());
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for (value, blinding) in values.iter().zip(blindings) {
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let (proof, commitment) = RangeProof::prove(*value, blinding, rng)?;
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proofs.push(proof);
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commitments.push(commitment);
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}
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Ok((Self { proofs }, commitments))
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}
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/// Verify aggregated range proofs
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pub fn verify(&self) -> Result<Vec<PedersenCommitment>> {
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let mut commitments = Vec::with_capacity(self.proofs.len());
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for proof in &self.proofs {
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commitments.push(proof.verify()?);
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}
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Ok(commitments)
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}
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/// Get the number of values this proof covers
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pub fn num_values(&self) -> usize {
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self.proofs.len()
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}
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/// Get the commitments this proof covers
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pub fn commitments(&self) -> Result<Vec<PedersenCommitment>> {
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self.proofs.iter().map(|p| p.commitment()).collect()
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}
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/// Get the total size of the proof in bytes
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pub fn size(&self) -> usize {
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self.proofs.iter().map(|p| p.size()).sum()
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}
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}
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/// Batch verifier for range proofs
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#[derive(Default)]
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pub struct BatchVerifier {
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single_proofs: Vec<RangeProof>,
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aggregated_proofs: Vec<AggregatedRangeProof>,
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}
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impl BatchVerifier {
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/// Create a new batch verifier
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pub fn new() -> Self {
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Self::default()
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}
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/// Add a single range proof to the batch
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pub fn add_single(&mut self, proof: RangeProof) {
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self.single_proofs.push(proof);
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}
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/// Add an aggregated range proof to the batch
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pub fn add_aggregated(&mut self, proof: AggregatedRangeProof) {
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self.aggregated_proofs.push(proof);
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}
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/// Verify all proofs in the batch
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pub fn verify_all(&self) -> Result<Vec<PedersenCommitment>> {
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let mut all_commitments = Vec::new();
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for proof in &self.single_proofs {
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all_commitments.push(proof.verify()?);
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}
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for proof in &self.aggregated_proofs {
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all_commitments.extend(proof.verify()?);
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}
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Ok(all_commitments)
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use rand::rngs::OsRng;
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#[test]
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fn test_single_range_proof() {
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let mut rng = OsRng;
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let blinding = BlindingFactor::random(&mut rng);
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let value = 1000u64;
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let (proof, commitment) = RangeProof::prove(value, &blinding, &mut rng).unwrap();
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// Verify the proof
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let verified = proof.verify().unwrap();
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assert_eq!(commitment.to_bytes(), verified.to_bytes());
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}
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#[test]
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fn test_range_proof_zero() {
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let mut rng = OsRng;
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let blinding = BlindingFactor::random(&mut rng);
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let value = 0u64;
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let (proof, _) = RangeProof::prove(value, &blinding, &mut rng).unwrap();
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assert!(proof.verify().is_ok());
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}
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#[test]
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fn test_range_proof_max() {
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let mut rng = OsRng;
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let blinding = BlindingFactor::random(&mut rng);
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let value = u64::MAX;
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let (proof, _) = RangeProof::prove(value, &blinding, &mut rng).unwrap();
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assert!(proof.verify().is_ok());
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}
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#[test]
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fn test_aggregated_range_proof() {
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let mut rng = OsRng;
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let values = vec![100u64, 200, 300, 400];
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let blindings: Vec<BlindingFactor> =
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(0..4).map(|_| BlindingFactor::random(&mut rng)).collect();
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let (proof, commitments) =
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AggregatedRangeProof::prove(&values, &blindings, &mut rng).unwrap();
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assert_eq!(commitments.len(), 4);
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assert_eq!(proof.num_values(), 4);
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let verified = proof.verify().unwrap();
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assert_eq!(verified.len(), commitments.len());
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}
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#[test]
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fn test_serialization() {
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let mut rng = OsRng;
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let blinding = BlindingFactor::random(&mut rng);
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let (proof, _) = RangeProof::prove(1000, &blinding, &mut rng).unwrap();
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// Borsh serialization
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let bytes = borsh::to_vec(&proof).unwrap();
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let recovered: RangeProof = borsh::from_slice(&bytes).unwrap();
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// Verify recovered proof
|
|
assert!(recovered.verify().is_ok());
|
|
}
|
|
}
|