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feat: constrain all unused cells to be zero #193

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Oct 19, 2023
Merged

feat: constrain all unused cells to be zero #193

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78 changes: 78 additions & 0 deletions hashes/zkevm/src/sha256/vanilla/constraints.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -424,6 +424,84 @@ impl<F: Field> Sha256CircuitConfig<F> {
cb.gate(meta.query_fixed(q_squeeze, Rotation::cur()))
});

// Constrain all unused cells to be 0 for safety.
#[allow(clippy::needless_range_loop)]
meta.create_gate("unused is zero", |meta| {
let to_const =
|value: &String| -> &'static str { Box::leak(value.clone().into_boxed_str()) };
let mut cb = BaseConstraintBuilder::new(MAX_DEGREE);

let q_start = meta.query_fixed(q_start, Rotation::cur());
let q_compression = meta.query_fixed(q_compression, Rotation::cur());
let q_input = meta.query_fixed(q_input, Rotation::cur());
let q_extend = meta.query_fixed(q_extend, Rotation::cur());
let q_end = meta.query_fixed(q_end, Rotation::cur());
let q_squeeze = meta.query_fixed(q_squeeze, Rotation::cur());

let is_final = meta.query_advice(is_final, Rotation::cur());
let is_paddings = is_paddings.map(|c| meta.query_advice(c, Rotation::cur()));
let word_value = meta.query_advice(hash_table.word_value, Rotation::cur());
let length = meta.query_advice(hash_table.length, Rotation::cur());
let output_lo = meta.query_advice(hash_table.output.lo(), Rotation::cur());
let output_hi = meta.query_advice(hash_table.output.hi(), Rotation::cur());

// column w.b0-w.b1 at offsets [0-19, 68-91, 140-255]
cb.condition(not::expr(q_extend.clone()), |cb| {
cb.require_zero("if not(q_extend) w.b0 = 0", w_ext[0].clone());
cb.require_zero("if not(q_extend) w.b1 = 0", w_ext[1].clone());
});
// column w.b2-w.b33 at offsets [0-3, 68-75, 140-255]
cb.condition(q_start.clone() + q_end.clone(), |cb| {
for k in 2..=33 {
cb.require_zero(
to_const(&format!("if q_start and q_end w.b{k} = 0")),
w_ext[k].clone(),
);
}
});
// column is_final at offsets [4, 20-70, 92-142, 144-255]
cb.condition(q_compression.clone() + q_end.clone() - q_squeeze.clone(), |cb| {
cb.require_zero(
"if q_compression or (q_end and not(q_squeeze)) is_final = 0",
is_final,
);
});
// column pad0-pad2 at offsets [0-3, 20-75, 92-255]
cb.condition(not::expr(q_input.clone()), |cb| {
for k in 0..=2 {
cb.require_zero(
to_const(&format!("if not(q_input) is_paddings[{k}] = 0")),
is_paddings[k].clone(),
);
}
});
// column pad3 at offsets [20-70, 92-142, 144-255]
cb.condition(q_extend.clone() + q_end.clone() - q_squeeze.clone(), |cb| {
cb.require_zero(
"if q_extend or (q_end and not(q_squeeze)) is_paddings[3] = 0",
is_paddings[3].clone(),
);
});
// column value at offsets [0-3, 20-75, 92-255]
cb.condition(not::expr(q_input.clone()), |cb| {
cb.require_zero("if not(q_input) hash_table.word_value = 0", word_value.clone());
});
// column len at offsets [20-70, 92-142, 144-255]
cb.condition(q_extend.clone() + q_end.clone() - q_squeeze.clone(), |cb| {
cb.require_zero(
"if q_extend or (q_end and not(q_squeeze)) hash_table.lenght = 0",
length.clone(),
);
});
// column out_lo, out_hi at offsets [0-70, 72-142, 144-255]
cb.condition(not::expr(q_squeeze.clone()), |cb| {
cb.require_zero("if not(q_squeeze) output_lo = 0", output_lo.clone());
cb.require_zero("if not(q_squeeze) output_hi = 0", output_hi.clone());
});

cb.gate(meta.query_fixed(q_enable, Rotation::cur()))
});

info!("degree: {}", meta.degree());

Sha256CircuitConfig {
Expand Down
23 changes: 15 additions & 8 deletions hashes/zkevm/src/sha256/vanilla/witness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -247,18 +247,23 @@ pub fn generate_witnesses_sha256(rows: &mut Vec<VirtualShaRow>, input_bytes: &[u
is_final,
length,
is_paddings,
hash_bytes: [u8; NUM_BYTES_TO_SQUEEZE]| {
hash_bytes: [u8; NUM_BYTES_TO_SQUEEZE],
is_input: bool| {
let word_to_bits = |value: u64, num_bits: usize| {
into_be_bits(&value.to_be_bytes())[64 - num_bits..64]
.iter()
.map(|b| *b != 0)
.collect::<Vec<_>>()
};
let mut word_bytes_be = (w as u32).to_be_bytes();
for (byte, is_padding) in word_bytes_be.iter_mut().zip(is_paddings) {
*byte = if is_padding { 0 } else { *byte };
}
let word_value = u32::from_le_bytes(word_bytes_be);
let word_value = if is_input {
let mut word_bytes_be = (w as u32).to_be_bytes();
for (byte, is_padding) in word_bytes_be.iter_mut().zip(is_paddings) {
*byte = if is_padding { 0 } else { *byte };
}
u32::from_le_bytes(word_bytes_be)
} else {
0
};
let hash_lo = u128::from_be_bytes(hash_bytes[16..].try_into().unwrap());
let hash_hi = u128::from_be_bytes(hash_bytes[..16].try_into().unwrap());
rows.push(VirtualShaRow {
Expand All @@ -282,7 +287,7 @@ pub fn generate_witnesses_sha256(rows: &mut Vec<VirtualShaRow>, input_bytes: &[u

// Add start rows
let mut add_row_start = |a: u64, e: u64, is_final| {
add_row(0, a, e, is_final, length, [false, false, false, in_padding], zero_hash)
add_row(0, a, e, is_final, length, [false, false, false, in_padding], zero_hash, false)
};
add_row_start(d, h, idx == 0);
add_row_start(c, g, idx == 0);
Expand Down Expand Up @@ -348,6 +353,7 @@ pub fn generate_witnesses_sha256(rows: &mut Vec<VirtualShaRow>, input_bytes: &[u
if round < NUM_WORDS_TO_ABSORB { length } else { 0 },
is_paddings,
zero_hash,
round < NUM_WORDS_TO_ABSORB,
);

// Truncate the newly calculated values
Expand Down Expand Up @@ -378,7 +384,7 @@ pub fn generate_witnesses_sha256(rows: &mut Vec<VirtualShaRow>, input_bytes: &[u

// Add end rows
let mut add_row_end = |a: u64, e: u64| {
add_row(0, a, e, false, 0, [false; ABSORB_WIDTH_PER_ROW_BYTES], zero_hash)
add_row(0, a, e, false, 0, [false; ABSORB_WIDTH_PER_ROW_BYTES], zero_hash, false)
};
add_row_end(hs[3], hs[7]);
add_row_end(hs[2], hs[6]);
Expand All @@ -391,6 +397,7 @@ pub fn generate_witnesses_sha256(rows: &mut Vec<VirtualShaRow>, input_bytes: &[u
length,
[false, false, false, in_padding],
hash_bytes,
false,
);

// Now truncate the results
Expand Down