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halo2/halo2_gadgets/src/sinsemilla/merkle/chip.rs

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//! Chip implementing a Merkle hash using Sinsemilla as the hash function.
use halo2_proofs::{
circuit::{AssignedCell, Chip, Layouter, Value},
plonk::{Advice, Column, ConstraintSystem, Constraints, Error, Selector},
poly::Rotation,
};
use pasta_curves::pallas;
use super::MerkleInstructions;
use crate::{
sinsemilla::{primitives as sinsemilla, MessagePiece},
utilities::RangeConstrained,
{
ecc::FixedPoints,
sinsemilla::{
chip::{SinsemillaChip, SinsemillaConfig},
CommitDomains, HashDomains, SinsemillaInstructions,
},
utilities::{
cond_swap::{CondSwapChip, CondSwapConfig, CondSwapInstructions},
UtilitiesInstructions,
},
},
};
use group::ff::PrimeField;
/// Configuration for the `MerkleChip` implementation.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct MerkleConfig<Hash, Commit, Fixed>
where
Hash: HashDomains<pallas::Affine>,
Fixed: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, Fixed, Hash>,
{
advices: [Column<Advice>; 5],
q_decompose: Selector,
pub(super) cond_swap_config: CondSwapConfig,
pub(super) sinsemilla_config: SinsemillaConfig<Hash, Commit, Fixed>,
}
/// Chip implementing `MerkleInstructions`.
///
/// This chip specifically implements `MerkleInstructions::hash_layer` as the `MerkleCRH`
/// function `hash = SinsemillaHash(Q, 𝑙⋆ || left⋆ || right⋆)`, where:
/// - `𝑙⋆ = I2LEBSP_10(l)`
/// - `left⋆ = I2LEBSP_255(left)`
/// - `right⋆ = I2LEBSP_255(right)`
///
/// This chip does **NOT** constrain `left⋆` and `right⋆` to be canonical encodings of
/// `left` and `right`.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct MerkleChip<Hash, Commit, Fixed>
where
Hash: HashDomains<pallas::Affine>,
Fixed: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, Fixed, Hash>,
{
config: MerkleConfig<Hash, Commit, Fixed>,
}
impl<Hash, Commit, Fixed> Chip<pallas::Base> for MerkleChip<Hash, Commit, Fixed>
where
Hash: HashDomains<pallas::Affine>,
Fixed: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, Fixed, Hash>,
{
type Config = MerkleConfig<Hash, Commit, Fixed>;
type Loaded = ();
fn config(&self) -> &Self::Config {
&self.config
}
fn loaded(&self) -> &Self::Loaded {
&()
}
}
impl<Hash, Commit, F> MerkleChip<Hash, Commit, F>
where
Hash: HashDomains<pallas::Affine>,
F: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, F, Hash>,
{
/// Configures the [`MerkleChip`].
pub fn configure(
meta: &mut ConstraintSystem<pallas::Base>,
sinsemilla_config: SinsemillaConfig<Hash, Commit, F>,
) -> MerkleConfig<Hash, Commit, F> {
// All five advice columns are equality-enabled by SinsemillaConfig.
let advices = sinsemilla_config.advices();
let cond_swap_config = CondSwapChip::configure(meta, advices);
// This selector enables the decomposition gate.
let q_decompose = meta.selector();
// Check that pieces have been decomposed correctly for Sinsemilla hash.
// <https://zips.z.cash/protocol/protocol.pdf#orchardmerklecrh>
//
// a = a_0||a_1 = l || (bits 0..=239 of left)
// b = b_0||b_1||b_2
// = (bits 240..=249 of left) || (bits 250..=254 of left) || (bits 0..=4 of right)
// c = bits 5..=254 of right
//
// The message pieces `a`, `b`, `c` are constrained by Sinsemilla to be
// 250 bits, 20 bits, and 250 bits respectively.
//
// The pieces and subpieces are arranged in the following configuration:
// | A_0 | A_1 | A_2 | A_3 | A_4 | q_decompose |
// -------------------------------------------------------
// | a | b | c | left | right | 1 |
// | z1_a | z1_b | b_1 | b_2 | l | 0 |
meta.create_gate("Decomposition check", |meta| {
let q_decompose = meta.query_selector(q_decompose);
let l_whole = meta.query_advice(advices[4], Rotation::next());
let two_pow_5 = pallas::Base::from(1 << 5);
let two_pow_10 = two_pow_5.square();
// a_whole is constrained by Sinsemilla to be 250 bits.
let a_whole = meta.query_advice(advices[0], Rotation::cur());
// b_whole is constrained by Sinsemilla to be 20 bits.
let b_whole = meta.query_advice(advices[1], Rotation::cur());
// c_whole is constrained by Sinsemilla to be 250 bits.
let c_whole = meta.query_advice(advices[2], Rotation::cur());
let left_node = meta.query_advice(advices[3], Rotation::cur());
let right_node = meta.query_advice(advices[4], Rotation::cur());
// a = a_0||a_1 = l || (bits 0..=239 of left)
//
// z_1 of SinsemillaHash(a) = a_1
// => a_0 = a - (a_1 * 2^10)
let z1_a = meta.query_advice(advices[0], Rotation::next());
let a_1 = z1_a;
// Derive a_0 (constrained by SinsemillaHash to be 10 bits)
let a_0 = a_whole - a_1.clone() * two_pow_10;
// b = b_0||b_1||b_2
// = (bits 240..=249 of left) || (bits 250..=254 of left) || (bits 0..=4 of right)
// The Orchard specification allows this representation to be non-canonical.
// <https://zips.z.cash/protocol/protocol.pdf#merklepath>
//
// z_1 of SinsemillaHash(b) = b_1 + 2^5 b_2
// => b_0 = b - (z1_b * 2^10)
let z1_b = meta.query_advice(advices[1], Rotation::next());
// b_1 has been constrained to be 5 bits outside this gate.
let b_1 = meta.query_advice(advices[2], Rotation::next());
// b_2 has been constrained to be 5 bits outside this gate.
let b_2 = meta.query_advice(advices[3], Rotation::next());
// Constrain b_1 + 2^5 b_2 = z1_b
// https://p.z.cash/halo2-0.1:sinsemilla-merkle-crh-bit-lengths?partial
let b1_b2_check = z1_b.clone() - (b_1.clone() + b_2.clone() * two_pow_5);
// Derive b_0 (constrained by SinsemillaHash to be 10 bits)
let b_0 = b_whole - (z1_b * two_pow_10);
// Check that left = a_1 (240 bits) || b_0 (10 bits) || b_1 (5 bits)
// https://p.z.cash/halo2-0.1:sinsemilla-merkle-crh-decomposition?partial
let left_check = {
let reconstructed = {
let two_pow_240 = pallas::Base::from_u128(1 << 120).square();
a_1 + (b_0 + b_1 * two_pow_10) * two_pow_240
};
reconstructed - left_node
};
// Check that right = b_2 (5 bits) || c (250 bits)
// The Orchard specification allows this representation to be non-canonical.
// <https://zips.z.cash/protocol/protocol.pdf#merklepath>
// https://p.z.cash/halo2-0.1:sinsemilla-merkle-crh-decomposition?partial
let right_check = b_2 + c_whole * two_pow_5 - right_node;
Constraints::with_selector(
q_decompose,
[
("l_check", a_0 - l_whole),
("left_check", left_check),
("right_check", right_check),
("b1_b2_check", b1_b2_check),
],
)
});
MerkleConfig {
advices,
q_decompose,
cond_swap_config,
sinsemilla_config,
}
}
/// Constructs a [`MerkleChip`] given a [`MerkleConfig`].
pub fn construct(config: MerkleConfig<Hash, Commit, F>) -> Self {
MerkleChip { config }
}
}
impl<Hash, Commit, F, const MERKLE_DEPTH: usize>
MerkleInstructions<pallas::Affine, MERKLE_DEPTH, { sinsemilla::K }, { sinsemilla::C }>
for MerkleChip<Hash, Commit, F>
where
Hash: HashDomains<pallas::Affine> + Eq,
F: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, F, Hash> + Eq,
{
#[allow(non_snake_case)]
fn hash_layer(
&self,
mut layouter: impl Layouter<pallas::Base>,
Q: pallas::Affine,
// l = MERKLE_DEPTH - layer - 1
l: usize,
left: Self::Var,
right: Self::Var,
) -> Result<Self::Var, Error> {
let config = self.config().clone();
// We need to hash `l || left || right`, where `l` is a 10-bit value.
// We allow `left` and `right` to be non-canonical 255-bit encodings.
//
// a = a_0||a_1 = l || (bits 0..=239 of left)
// b = b_0||b_1||b_2
// = (bits 240..=249 of left) || (bits 250..=254 of left) || (bits 0..=4 of right)
// c = bits 5..=254 of right
//
// We start by witnessing all of the individual pieces, and range-constraining the
// short pieces b_1 and b_2.
//
// https://p.z.cash/halo2-0.1:sinsemilla-merkle-crh-bit-lengths?partial
// `a = a_0||a_1` = `l` || (bits 0..=239 of `left`)
let a = MessagePiece::from_subpieces(
self.clone(),
layouter.namespace(|| "Witness a = a_0 || a_1"),
[
RangeConstrained::bitrange_of(Value::known(&pallas::Base::from(l as u64)), 0..10),
RangeConstrained::bitrange_of(left.value(), 0..240),
],
)?;
// b = b_0 || b_1 || b_2
// = (bits 240..=249 of left) || (bits 250..=254 of left) || (bits 0..=4 of right)
let (b_1, b_2, b) = {
// b_0 = (bits 240..=249 of `left`)
let b_0 = RangeConstrained::bitrange_of(left.value(), 240..250);
// b_1 = (bits 250..=254 of `left`)
// Constrain b_1 to 5 bits.
let b_1 = RangeConstrained::witness_short(
&config.sinsemilla_config.lookup_config(),
layouter.namespace(|| "b_1"),
left.value(),
250..(pallas::Base::NUM_BITS as usize),
)?;
// b_2 = (bits 0..=4 of `right`)
// Constrain b_2 to 5 bits.
let b_2 = RangeConstrained::witness_short(
&config.sinsemilla_config.lookup_config(),
layouter.namespace(|| "b_2"),
right.value(),
0..5,
)?;
let b = MessagePiece::from_subpieces(
self.clone(),
layouter.namespace(|| "Witness b = b_0 || b_1 || b_2"),
[b_0, b_1.value(), b_2.value()],
)?;
(b_1, b_2, b)
};
// c = bits 5..=254 of `right`
let c = MessagePiece::from_subpieces(
self.clone(),
layouter.namespace(|| "Witness c"),
[RangeConstrained::bitrange_of(
right.value(),
5..(pallas::Base::NUM_BITS as usize),
)],
)?;
// hash = SinsemillaHash(Q, 𝑙⋆ || left⋆ || right⋆)
//
// `hash = ⊥` is handled internally to `SinsemillaChip::hash_to_point`: incomplete
// addition constraints allows ⊥ to occur, and then during synthesis it detects
// these edge cases and raises an error (aborting proof creation).
//
// Note that MerkleCRH as-defined maps ⊥ to 0. This is for completeness outside
// the circuit (so that the ⊥ does not propagate into the type system). The chip
// explicitly doesn't map ⊥ to 0; in fact it cannot, as doing so would require
// constraints that amount to using complete addition. The rationale for excluding
// this map is the same as why Sinsemilla uses incomplete addition: this situation
// yields a nontrivial discrete log relation, and by assumption it is hard to find
// these.
//
// https://p.z.cash/proto:merkle-crh-orchard
let (point, zs) = self.hash_to_point(
layouter.namespace(|| format!("hash at l = {}", l)),
Q,
vec![a.inner(), b.inner(), c.inner()].into(),
)?;
let hash = Self::extract(&point);
// `SinsemillaChip::hash_to_point` returns the running sum for each `MessagePiece`.
// Grab the outputs we need for the decomposition constraints.
let z1_a = zs[0][1].clone();
let z1_b = zs[1][1].clone();
// Check that the pieces have been decomposed properly.
//
// The pieces and subpieces are arranged in the following configuration:
// | A_0 | A_1 | A_2 | A_3 | A_4 | q_decompose |
// -------------------------------------------------------
// | a | b | c | left | right | 1 |
// | z1_a | z1_b | b_1 | b_2 | l | 0 |
{
layouter.assign_region(
|| "Check piece decomposition",
|mut region| {
// Set the fixed column `l` to the current l.
// Recall that l = MERKLE_DEPTH - layer - 1.
// The layer with 2^n nodes is called "layer n".
config.q_decompose.enable(&mut region, 0)?;
region.assign_advice_from_constant(
|| format!("l {}", l),
config.advices[4],
1,
pallas::Base::from(l as u64),
)?;
// Offset 0
// Copy and assign `a` at the correct position.
a.inner().cell_value().copy_advice(
|| "copy a",
&mut region,
config.advices[0],
0,
)?;
// Copy and assign `b` at the correct position.
b.inner().cell_value().copy_advice(
|| "copy b",
&mut region,
config.advices[1],
0,
)?;
// Copy and assign `c` at the correct position.
c.inner().cell_value().copy_advice(
|| "copy c",
&mut region,
config.advices[2],
0,
)?;
// Copy and assign the left node at the correct position.
left.copy_advice(|| "left", &mut region, config.advices[3], 0)?;
// Copy and assign the right node at the correct position.
right.copy_advice(|| "right", &mut region, config.advices[4], 0)?;
// Offset 1
// Copy and assign z_1 of SinsemillaHash(a) = a_1
z1_a.copy_advice(|| "z1_a", &mut region, config.advices[0], 1)?;
// Copy and assign z_1 of SinsemillaHash(b) = b_1
z1_b.copy_advice(|| "z1_b", &mut region, config.advices[1], 1)?;
// Copy `b_1`, which has been constrained to be a 5-bit value
b_1.inner()
.copy_advice(|| "b_1", &mut region, config.advices[2], 1)?;
// Copy `b_2`, which has been constrained to be a 5-bit value
b_2.inner()
.copy_advice(|| "b_2", &mut region, config.advices[3], 1)?;
Ok(())
},
)?;
}
// Check layer hash output against Sinsemilla primitives hash
#[cfg(test)]
{
use crate::{sinsemilla::primitives::HashDomain, utilities::i2lebsp};
use group::ff::PrimeFieldBits;
left.value()
.zip(right.value())
.zip(hash.value())
.assert_if_known(|((left, right), hash)| {
let l = i2lebsp::<10>(l as u64);
let left: Vec<_> = left
.to_le_bits()
.iter()
.by_vals()
.take(pallas::Base::NUM_BITS as usize)
.collect();
let right: Vec<_> = right
.to_le_bits()
.iter()
.by_vals()
.take(pallas::Base::NUM_BITS as usize)
.collect();
let merkle_crh = HashDomain::from_Q(Q.into());
let mut message = l.to_vec();
message.extend_from_slice(&left);
message.extend_from_slice(&right);
let expected = merkle_crh.hash(message.into_iter()).unwrap();
expected.to_repr() == hash.to_repr()
});
}
Ok(hash)
}
}
impl<Hash, Commit, F> UtilitiesInstructions<pallas::Base> for MerkleChip<Hash, Commit, F>
where
Hash: HashDomains<pallas::Affine>,
F: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, F, Hash>,
{
type Var = AssignedCell<pallas::Base, pallas::Base>;
}
impl<Hash, Commit, F> CondSwapInstructions<pallas::Base> for MerkleChip<Hash, Commit, F>
where
Hash: HashDomains<pallas::Affine>,
F: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, F, Hash>,
{
#[allow(clippy::type_complexity)]
fn swap(
&self,
layouter: impl Layouter<pallas::Base>,
pair: (Self::Var, Value<pallas::Base>),
swap: Value<bool>,
) -> Result<(Self::Var, Self::Var), Error> {
let config = self.config().cond_swap_config.clone();
let chip = CondSwapChip::<pallas::Base>::construct(config);
chip.swap(layouter, pair, swap)
}
}
impl<Hash, Commit, F> SinsemillaInstructions<pallas::Affine, { sinsemilla::K }, { sinsemilla::C }>
for MerkleChip<Hash, Commit, F>
where
Hash: HashDomains<pallas::Affine>,
F: FixedPoints<pallas::Affine>,
Commit: CommitDomains<pallas::Affine, F, Hash>,
{
type CellValue = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::CellValue;
type Message = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::Message;
type MessagePiece = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::MessagePiece;
type RunningSum = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::RunningSum;
type X = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::X;
type NonIdentityPoint = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::NonIdentityPoint;
type FixedPoints = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::FixedPoints;
type HashDomains = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::HashDomains;
type CommitDomains = <SinsemillaChip<Hash, Commit, F> as SinsemillaInstructions<
pallas::Affine,
{ sinsemilla::K },
{ sinsemilla::C },
>>::CommitDomains;
fn witness_message_piece(
&self,
layouter: impl Layouter<pallas::Base>,
value: Value<pallas::Base>,
num_words: usize,
) -> Result<Self::MessagePiece, Error> {
let config = self.config().sinsemilla_config.clone();
let chip = SinsemillaChip::<Hash, Commit, F>::construct(config);
chip.witness_message_piece(layouter, value, num_words)
}
#[allow(non_snake_case)]
#[allow(clippy::type_complexity)]
fn hash_to_point(
&self,
layouter: impl Layouter<pallas::Base>,
Q: pallas::Affine,
message: Self::Message,
) -> Result<(Self::NonIdentityPoint, Vec<Vec<Self::CellValue>>), Error> {
let config = self.config().sinsemilla_config.clone();
let chip = SinsemillaChip::<Hash, Commit, F>::construct(config);
chip.hash_to_point(layouter, Q, message)
}
fn extract(point: &Self::NonIdentityPoint) -> Self::X {
SinsemillaChip::<Hash, Commit, F>::extract(point)
}
}
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