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Move Pedersen hash functions to their own submodule

This commit is contained in:
Deirdre Connolly 2020-08-07 05:16:55 -04:00 committed by Deirdre Connolly
parent be7ea200c8
commit 014afd8e4a
4 changed files with 150 additions and 134 deletions
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135
zebra-chain/src/commitments/sapling.rs
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@ -5,6 +5,8 @@ mod arbitrary;
#[cfg(test)]
mod test_vectors;
pub mod pedersen_hashes;
use std::{fmt, io};
use bitvec::prelude::*;
@ -17,138 +19,7 @@ use crate::{
types::amount::{Amount, NonNegative},
};
/// Generates a random scalar from the scalar field 𝔽_{r_𝕁}.
///
/// The prime order subgroup 𝕁^(r) is the order-r_𝕁 subgroup of 𝕁 that consists
/// of the points whose order divides r. This function is useful when generating
/// the uniform distribution on 𝔽_{r_𝕁} needed for Sapling commitment schemes'
/// trapdoor generators.
///
/// https://zips.z.cash/protocol/protocol.pdf#jubjub
pub fn generate_trapdoor<T>(csprng: &mut T) -> jubjub::Fr
where
T: RngCore + CryptoRng,
{
let mut bytes = [0u8; 64];
csprng.fill_bytes(&mut bytes);
// Fr::from_bytes_wide() reduces the input modulo r via Fr::from_u512()
jubjub::Fr::from_bytes_wide(&bytes)
}
/// "...an algebraic hash function with collision resistance (for fixed input
/// length) derived from assumed hardness of the Discrete Logarithm Problem on
/// the Jubjub curve."
///
/// PedersenHash is used in the definitions of Pedersen commitments (§
/// 5.4.7.2 ‘Windowed Pedersen commitments’), and of the Pedersen hash for the
/// Sapling incremental Merkle tree (§ 5.4.1.3 ‘MerkleCRH^Sapling Hash
/// Function’).
///
/// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
#[allow(non_snake_case)]
pub fn pedersen_hash_to_point(domain: [u8; 8], M: &BitVec<Lsb0, u8>) -> jubjub::ExtendedPoint {
// Expects i to be 1-indexed from the loop it's called in.
fn I_i(domain: [u8; 8], i: u32) -> jubjub::ExtendedPoint {
find_group_hash(domain, &(i - 1).to_le_bytes())
}
/// ⟨Mᵢ⟩
///
/// Σ j={0,k-1}: (1 - 2x₂)⋅(1 + x₀ + 2x₁)⋅2^(4⋅j)
// This is less efficient than it could be so that it can match the math
// closely.
fn M_i(segment: &BitSlice<Lsb0, u8>) -> jubjub::Fr {
let mut m_i = jubjub::Fr::zero();
for (j, chunk) in segment.chunks(3).enumerate() {
// Pad each chunk with zeros.
let mut store = 0u8;
let bits = store.bits_mut::<Lsb0>();
chunk
.iter()
.enumerate()
.for_each(|(i, bit)| bits.set(i, *bit));
let mut tmp = jubjub::Fr::one();
if bits[0] {
tmp += &jubjub::Fr::one();
}
if bits[1] {
tmp += &jubjub::Fr::one().double();
}
if bits[2] {
tmp -= tmp.double();
}
if j > 0 {
// Inclusive range!
tmp *= (1..=(4 * j)).fold(jubjub::Fr::one(), |acc, _| acc.double());
}
m_i += tmp;
}
m_i
}
let mut result = jubjub::ExtendedPoint::identity();
// Split M into n segments of 3 * c bits, where c = 63, padding the last
// segment with zeros.
//
// This loop is 1-indexed per the math definitions in the spec.
//
// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
for (i, segment) in M
.chunks(189)
.enumerate()
.map(|(i, segment)| (i + 1, segment))
{
result += I_i(domain, i as u32) * M_i(&segment);
}
result
}
/// Pedersen Hash Function
///
/// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
#[allow(non_snake_case)]
pub fn pedersen_hash(domain: [u8; 8], M: &BitVec<Lsb0, u8>) -> jubjub::Fq {
jubjub::AffinePoint::from(pedersen_hash_to_point(domain, M)).get_u()
}
/// Mixing Pedersen Hash Function
///
/// Used to compute ρ from a note commitment and its position in the note
/// commitment tree. It takes as input a Pedersen commitment P, and hashes it
/// with another input x.
///
/// MixingPedersenHash(P, x) := P + [x]FindGroupHash^J^(r)(“Zcash_J_”, “”)
///
/// https://zips.z.cash/protocol/protocol.pdf#concretemixinghash
#[allow(non_snake_case)]
pub fn mixing_pedersen_hash(P: jubjub::ExtendedPoint, x: jubjub::Fr) -> jubjub::ExtendedPoint {
const J: [u8; 8] = *b"Zcash_J_";
P + find_group_hash(J, b"") * x
}
/// Construct a 'windowed' Pedersen commitment by reusing a Pederson hash
/// construction, and adding a randomized point on the Jubjub curve.
///
/// WindowedPedersenCommit_r (s) := \
/// PedersenHashToPoint(“Zcash_PH”, s) + [r]FindGroupHash^J^(r)(“Zcash_PH”, “r”)
///
/// https://zips.z.cash/protocol/protocol.pdf#concretewindowedcommit
pub fn windowed_pedersen_commitment(r: jubjub::Fr, s: &BitVec<Lsb0, u8>) -> jubjub::ExtendedPoint {
const D: [u8; 8] = *b"Zcash_PH";
pedersen_hash_to_point(D, &s) + find_group_hash(D, b"r") * r
}
use pedersen_hashes::*;
/// The randomness used in the Pedersen Hash for note commitment.
#[derive(Copy, Clone, Debug, PartialEq)]

145
zebra-chain/src/commitments/sapling/pedersen_hashes.rs Normal file
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@ -0,0 +1,145 @@
//! Pedersen hash functions and helpers.
use bitvec::prelude::*;
use rand_core::{CryptoRng, RngCore};
use crate::keys::sapling::find_group_hash;
/// I_i
///
/// Expects i to be 1-indexed from the loop it's called in.
///
/// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
#[allow(non_snake_case)]
fn I_i(domain: [u8; 8], i: u32) -> jubjub::ExtendedPoint {
find_group_hash(domain, &(i - 1).to_le_bytes())
}
/// The encoding function ⟨Mᵢ⟩
///
/// Σ j={0,k-1}: (1 - 2x₂)⋅(1 + x₀ + 2x₁)⋅2^(4⋅j)
///
/// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
#[allow(non_snake_case)]
fn M_i(segment: &BitSlice<Lsb0, u8>) -> jubjub::Fr {
let mut m_i = jubjub::Fr::zero();
for (j, chunk) in segment.chunks(3).enumerate() {
// Pad each chunk with zeros.
let mut store = 0u8;
let bits = store.bits_mut::<Lsb0>();
chunk
.iter()
.enumerate()
.for_each(|(i, bit)| bits.set(i, *bit));
let mut tmp = jubjub::Fr::one();
if bits[0] {
tmp += &jubjub::Fr::one();
}
if bits[1] {
tmp += &jubjub::Fr::one().double();
}
if bits[2] {
tmp -= tmp.double();
}
if j > 0 {
// Inclusive range!
tmp *= (1..=(4 * j)).fold(jubjub::Fr::one(), |acc, _| acc.double());
}
m_i += tmp;
}
m_i
}
/// "...an algebraic hash function with collision resistance (for fixed input
/// length) derived from assumed hardness of the Discrete Logarithm Problem on
/// the Jubjub curve."
///
/// PedersenHash is used in the definitions of Pedersen commitments (§
/// 5.4.7.2 ‘Windowed Pedersen commitments’), and of the Pedersen hash for the
/// Sapling incremental Merkle tree (§ 5.4.1.3 ‘MerkleCRH^Sapling Hash
/// Function’).
///
/// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
#[allow(non_snake_case)]
pub fn pedersen_hash_to_point(domain: [u8; 8], M: &BitVec<Lsb0, u8>) -> jubjub::ExtendedPoint {
let mut result = jubjub::ExtendedPoint::identity();
// Split M into n segments of 3 * c bits, where c = 63, padding the last
// segment with zeros.
//
// This loop is 1-indexed per the math definitions in the spec.
//
// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
for (i, segment) in M
.chunks(189)
.enumerate()
.map(|(i, segment)| (i + 1, segment))
{
result += I_i(domain, i as u32) * M_i(&segment);
}
result
}
/// Pedersen Hash Function
///
/// https://zips.z.cash/protocol/protocol.pdf#concretepedersenhash
#[allow(non_snake_case)]
pub fn pedersen_hash(domain: [u8; 8], M: &BitVec<Lsb0, u8>) -> jubjub::Fq {
jubjub::AffinePoint::from(pedersen_hash_to_point(domain, M)).get_u()
}
/// Mixing Pedersen Hash Function
///
/// Used to compute ρ from a note commitment and its position in the note
/// commitment tree. It takes as input a Pedersen commitment P, and hashes it
/// with another input x.
///
/// MixingPedersenHash(P, x) := P + [x]FindGroupHash^J^(r)(“Zcash_J_”, “”)
///
/// https://zips.z.cash/protocol/protocol.pdf#concretemixinghash
#[allow(non_snake_case)]
pub fn mixing_pedersen_hash(P: jubjub::ExtendedPoint, x: jubjub::Fr) -> jubjub::ExtendedPoint {
const J: [u8; 8] = *b"Zcash_J_";
P + find_group_hash(J, b"") * x
}
/// Construct a 'windowed' Pedersen commitment by reusing a Pederson hash
/// construction, and adding a randomized point on the Jubjub curve.
///
/// WindowedPedersenCommit_r (s) := \
/// PedersenHashToPoint(“Zcash_PH”, s) + [r]FindGroupHash^J^(r)(“Zcash_PH”, “r”)
///
/// https://zips.z.cash/protocol/protocol.pdf#concretewindowedcommit
pub fn windowed_pedersen_commitment(r: jubjub::Fr, s: &BitVec<Lsb0, u8>) -> jubjub::ExtendedPoint {
const D: [u8; 8] = *b"Zcash_PH";
pedersen_hash_to_point(D, &s) + find_group_hash(D, b"r") * r
}
/// Generates a random scalar from the scalar field 𝔽_{r_𝕁}.
///
/// The prime order subgroup 𝕁^(r) is the order-r_𝕁 subgroup of 𝕁 that consists
/// of the points whose order divides r. This function is useful when generating
/// the uniform distribution on 𝔽_{r_𝕁} needed for Sapling commitment schemes'
/// trapdoor generators.
///
/// https://zips.z.cash/protocol/protocol.pdf#jubjub
pub fn generate_trapdoor<T>(csprng: &mut T) -> jubjub::Fr
where
T: RngCore + CryptoRng,
{
let mut bytes = [0u8; 64];
csprng.fill_bytes(&mut bytes);
// Fr::from_bytes_wide() reduces the input modulo r via Fr::from_u512()
jubjub::Fr::from_bytes_wide(&bytes)
}

2
zebra-chain/src/notes/sapling/nullifiers.rs
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@ -4,7 +4,7 @@
use std::io;
use crate::{
commitments::sapling::{mixing_pedersen_hash, NoteCommitment},
commitments::sapling::{pedersen_hashes::mixing_pedersen_hash, NoteCommitment},
keys::sapling::NullifierDerivingKey,
serialization::{ReadZcashExt, SerializationError, ZcashDeserialize, ZcashSerialize},
treestate::note_commitment_tree::Position,

2
zebra-chain/src/treestate/note_commitment_tree.rs
View File

@ -20,7 +20,7 @@ use bitvec::prelude::*;
use proptest_derive::Arbitrary;
use crate::{
commitments::sapling::pedersen_hash,
commitments::sapling::pedersen_hashes::pedersen_hash,
serialization::{SerializationError, ZcashDeserialize, ZcashSerialize},
};