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Further cleanups and docfixes.
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Co-authored-by: Daira Hopwood <[email protected]>
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@therealyingtong @daira
therealyingtong and daira committed Jun 29, 2021
1 parent d68eb65 commit 3806a9d
Showing 1 changed file with 46 additions and 22 deletions.
68 changes: 46 additions & 22 deletions src/circuit/gadget/sinsemilla/merkle/chip.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,13 +71,13 @@ impl MerkleChip {
// This fixed column serves two purposes:
// - Fixing the value of l* for rows in which a Merkle path layer
// is decomposed.
// - Disabling the entire decomposition gate (when set to zero)
// - Disabling the entire decomposition gate when set to zero
// (i.e. replacing a Selector).

let l_plus_1 = meta.fixed_column();

// Check that pieces have been decomposed correctly for Sinsemilla hash.
// <https://zips.z.cash/protocol/nu5.pdf#orchardmerklecrh>
// <https://zips.z.cash/protocol/protocol.pdf#orchardmerklecrh>
//
// a = a_0||a_1 = l_star || (bits 0..=239 of left)
// b = b_0||b_1||b_2
Expand All @@ -87,6 +87,13 @@ impl MerkleChip {
// 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 | l_plus_1 |
----------------------------------------------------
| a | b | c | left | right | l + 1 |
| z1_a | z1_b | b_1 | b_2 | | |
*/
meta.create_gate("Decomposition check", |meta| {
let l_plus_1_whole = meta.query_fixed(l_plus_1, Rotation::cur());

Expand Down Expand Up @@ -115,6 +122,8 @@ impl MerkleChip {

// 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)
Expand All @@ -132,18 +141,23 @@ impl MerkleChip {
let left_check = {
let reconstructed = {
let two_pow_240 = pallas::Base::from_u128(1 << 120).square();
let b0_shifted = b_0 * two_pow_240;
let b1_shifted = b_1 * two_pow_240 * two_pow_10;
a_1 + b0_shifted + b1_shifted
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>
let right_check = b_2 + c_whole * two_pow_5 - right_node;

array::IntoIter::new([l_star_check, left_check, right_check, b1_b2_check])
.map(move |poly| l_plus_1_whole.clone() * poly)
array::IntoIter::new([
("l_star_check", l_star_check),
("left_check", left_check),
("right_check", right_check),
("b1_b2_check", b1_b2_check),
])
.map(move |(name, poly)| (name, l_plus_1_whole.clone() * poly))
});

MerkleConfig {
Expand All @@ -169,13 +183,14 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
&self,
mut layouter: impl Layouter<pallas::Base>,
Q: pallas::Affine,
l_star: usize,
left: <Self as UtilitiesInstructions<pallas::Base>>::Var,
right: <Self as UtilitiesInstructions<pallas::Base>>::Var,
) -> Result<<Self as UtilitiesInstructions<pallas::Base>>::Var, Error> {
// l = MERKLE_DEPTH_ORCHARD - layer - 1
l: usize,
left: Self::Var,
right: Self::Var,
) -> Result<Self::Var, Error> {
let config = self.config().clone();

// <https://zips.z.cash/protocol/nu5.pdf#orchardmerklecrh>
// <https://zips.z.cash/protocol/protocol.pdf#orchardmerklecrh>
// We need to hash `l_star || left || right`, where `l_star` is a 10-bit value.
// We allow `left` and `right` to be non-canonical 255-bit encodings.
//
Expand All @@ -184,11 +199,11 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
// = (bits 240..=249 of left) || (bits 250..=254 of left) || (bits 0..=4 of right)
// c = bits 5..=254 of right

// `a = a_0||a_1` = `l` || (bits 0..=239 of `left`)
// `a = a_0||a_1` = `l_star` || (bits 0..=239 of `left`)
let a = {
let a = {
// a_0 = l_star
let a_0 = bitrange_subset(pallas::Base::from_u64(l_star as u64), 0..10);
let a_0 = bitrange_subset(pallas::Base::from_u64(l as u64), 0..10);

// a_1 = (bits 0..=239 of `left`)
let a_1 = left.value().map(|value| bitrange_subset(value, 0..240));
Expand All @@ -199,7 +214,7 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
self.witness_message_piece(layouter.namespace(|| "Witness a = a_0 || a_1"), a, 25)?
};

// b = b_0||b_1||b_2
// 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`)
Expand Down Expand Up @@ -238,7 +253,7 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
+ b_2 * pallas::Base::from_u64(1 << 15)
});
self.witness_message_piece(
layouter.namespace(|| "Witness b = b_0||b_1||b_2||b_3"),
layouter.namespace(|| "Witness b = b_0 || b_1 || b_2"),
b,
2,
)?
Expand All @@ -256,20 +271,29 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
};

let (point, zs) = self.hash_to_point(
layouter.namespace(|| format!("l_star {}", l_star)),
layouter.namespace(|| format!("hash at l = {}", l)),
Q,
vec![a, b, c].into(),
)?;
let z1_a = zs[0][1];
let z1_b = zs[1][1];

// 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 | l_plus_1 |
----------------------------------------------------
| a | b | c | left | right | l + 1 |
| z1_a | z1_b | b_1 | b_2 | | |
*/
{
layouter.assign_region(
|| "Check piece decomposition",
|mut region| {
// Set the fixed column `l_plus_1` to the current l_star + 1.
let l_plus_1 = (l_star as u64) + 1;
// Set the fixed column `l_plus_1` to the current l + 1.
// Recall that l = MERKLE_DEPTH_ORCHARD - layer - 1.
// The layer with 2^n nodes is called "layer n".
let l_plus_1 = (l as u64) + 1;
region.assign_fixed(
|| format!("l_plus_1 {}", l_plus_1),
config.l_plus_1,
Expand Down Expand Up @@ -328,7 +352,7 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
// Copy and assign z_1 of SinsemillaHash(a) = a_1
copy(
&mut region,
|| "a_0",
|| "z1_a",
config.advices[0],
1,
&z1_a,
Expand All @@ -337,7 +361,7 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
// Copy and assign z_1 of SinsemillaHash(b) = b_1
copy(
&mut region,
|| "b_0",
|| "z1_b",
config.advices[1],
1,
&z1_b,
Expand Down Expand Up @@ -378,7 +402,7 @@ impl MerkleInstructions<pallas::Affine, MERKLE_DEPTH_ORCHARD, { sinsemilla::K },
};

if let (Some(left), Some(right)) = (left.value(), right.value()) {
let l_star = i2lebsp::<10>(l_star as u64);
let l_star = i2lebsp::<10>(l as u64);
let left: Vec<_> = left
.to_le_bits()
.iter()
Expand Down

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