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[Zellic Audit] 3.12 Incomplete handling of G1 point addition #379

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Merged
Hakkush-07 merged 5 commits into from
Nov 11, 2025
Merged

[Zellic Audit] 3.12 Incomplete handling of G1 point addition #379

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75ed48d
create a version of G1Affine::hinted_check_add that the caller must u…
Hakkush-07 Sep 11, 2025
d5a1dac
optimize G1Affine::hinted_check_add and add TODO comments for later
Hakkush-07 Sep 19, 2025
4f8cc34
rearrange wrong if checks in G1Affine::hinted_check_add
Hakkush-07 Oct 13, 2025
d6bad4f
add validity checks to hints of new G1Affine::hinted_check_add
Hakkush-07 Oct 13, 2025
1e2f665
fix hint validity check and roll in G1Affine::hinted_check_add
Hakkush-07 Oct 14, 2025
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16 changes: 16 additions & 0 deletions bitvm/src/bigint/cmp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,22 @@ impl<const N_BITS: u32, const LIMB_SIZE: u32> BigIntImpl<N_BITS, LIMB_SIZE> {
}
}

pub fn equal_keep_elements(a: u32, b: u32) -> Script {
script! {
{ Self::copy_zip(a, b) }
for _ in 0..Self::N_LIMBS {
OP_EQUAL
OP_TOALTSTACK
}
for _ in 0..Self::N_LIMBS {
OP_FROMALTSTACK
}
for _ in 0..Self::N_LIMBS - 1 {
OP_BOOLAND
}
}
}

pub fn notequal(a: u32, b: u32) -> Script {
script! {
{ Self::equal(a, b) }
Expand Down
5 changes: 5 additions & 0 deletions bitvm/src/bn254/fp254impl.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,11 @@ pub trait Fp254Impl {
U254::equal(a, b)
}

#[inline]
fn equal_keep_elements(a: u32, b: u32) -> Script {
U254::equal_keep_elements(a, b)
}

#[inline]
fn equalverify(a: u32, b: u32) -> Script {
U254::equalverify(a, b)
Expand Down
173 changes: 148 additions & 25 deletions bitvm/src/bn254/g1.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -155,8 +155,13 @@ impl G1Affine {
}
}

pub fn hinted_check_add(t: ark_bn254::G1Affine, q: ark_bn254::G1Affine) -> (Script, Vec<Hint>) {
pub fn hinted_check_add_prevent_degenerate(
t: ark_bn254::G1Affine,
q: ark_bn254::G1Affine,
) -> (Script, Vec<Hint>) {
let mut hints = vec![];
assert_ne!(t, q);
assert_ne!(t, -q);

let (alpha, bias) = if !t.is_zero() && !q.is_zero() {
let alpha = (t.y - q.y) / (t.x - q.x);
Expand Down Expand Up @@ -212,6 +217,106 @@ impl G1Affine {
(script, hints)
}

pub fn hinted_check_add(t: ark_bn254::G1Affine, q: ark_bn254::G1Affine) -> (Script, Vec<Hint>) {
let mut hints = vec![];

let (alpha, bias) = if t.is_zero() || q.is_zero() {
// no hint, dummy zero
(ark_bn254::Fq::ZERO, ark_bn254::Fq::ZERO)
} else if t == -q {
// no hint, dummy zero
(ark_bn254::Fq::ZERO, ark_bn254::Fq::ZERO)
} else if t == q {
// doubling hints
let alpha = (t.x.square() + t.x.square() + t.x.square()) / (t.y + t.y);
let bias = t.y - alpha * t.x;
(alpha, bias)
} else {
// adding hints
let alpha = (t.y - q.y) / (t.x - q.x);
let bias = t.y - alpha * t.x;
(alpha, bias)
};

let (hinted_script1, hint1) = Self::hinted_check_chord_line(t, q, alpha);
let (hinted_script2, hint2) = Self::hinted_add(t.x, q.x, alpha);
let (hinted_script3, hint3) = Self::hinted_check_tangent_line(t, alpha);

let script = script! { // tx ty qx qy
{ G1Affine::is_zero_keep_element() }
OP_IF
{ G1Affine::drop() }
OP_ELSE
{ G1Affine::roll(2) }
{ G1Affine::is_zero_keep_element() }
OP_IF
{ G1Affine::drop() }
OP_ELSE // qx qy tx ty
{ Fq::equal_keep_elements(3, 1) } // t == q or t == -q
OP_DUP
OP_TOALTSTACK
OP_TOALTSTACK
{ Fq::equal_keep_elements(2, 0) }
OP_NOT
OP_FROMALTSTACK
OP_BOOLAND
OP_IF // case: t == -q
OP_FROMALTSTACK OP_DROP
{ G1Affine::drop() }
{ G1Affine::drop() }
{ G1Affine::identity() }
OP_ELSE // case: t != -q
for _ in 0..Fq::N_LIMBS {
OP_DEPTH OP_1SUB OP_ROLL
}
{ Fq::check_validity_and_keep_element() }
for _ in 0..Fq::N_LIMBS {
OP_DEPTH OP_1SUB OP_ROLL
} // qx qy tx ty c3 c4
{ Fq::check_validity_and_keep_element() }
{ Fq::copy(1) } // qx qy tx ty c3 c4 c3
{ Fq::copy(1) } // qx qy tx ty c3 c4 c3 c4
{ Fq::copy(5) } // qx qy tx ty c3 c4 c3 c4 tx
{ Fq::roll(5) } // qx qy tx c3 c4 c3 c4 tx ty
OP_FROMALTSTACK
OP_IF // case: t == q
{ hinted_script3 } // qx qy tx c3 c4 is_tangent_line_correct
OP_VERIFY // qx qy tx c3 c4
{ Fq::roll(3) } // qx tx c3 c4 qy
{ Fq::drop() } // qx tx c3 c4
OP_ELSE // case: general case
{ Fq::copy(8) } // qx qy tx c3 c4 c3 c4 tx ty qx
{ Fq::roll(8) } // qx tx c3 c4 c3 c4 tx ty qx qy
{ hinted_script1 } // qx tx c3 c4 0/1
OP_VERIFY // qx tx c3 c4
OP_ENDIF
{ Fq::roll(2) } // qx c3 c4 tx
{ Fq::roll(3) } // c3 c4 tx qx
{ hinted_script2 } // x' y'
OP_ENDIF
OP_ENDIF
OP_ENDIF
};

if t.is_zero() || q.is_zero() {
// no hint
} else if t == -q {
// no hint
} else if t == q {
hints.push(Hint::Fq(alpha));
hints.push(Hint::Fq(-bias));
hints.extend(hint3);
hints.extend(hint2);
} else {
hints.push(Hint::Fq(alpha));
hints.push(Hint::Fq(-bias));
hints.extend(hint1);
hints.extend(hint2);
};

(script, hints)
}

/// add two points T and Q
/// x' = alpha^2 - T.x - Q.x
/// y' = -bias - alpha * x'
Expand Down Expand Up @@ -659,50 +764,68 @@ mod test {
}

#[test]
fn test_g1_affine_hinted_check_add() {
//println!("G1.hinted_add: {} bytes", G1Affine::check_add().len());
fn test_g1_affine_hinted_check_add_prevent_degenerate() {
let mut prng = ChaCha20Rng::seed_from_u64(0);
let t = ark_bn254::G1Affine::rand(&mut prng);
let q = ark_bn254::G1Affine::rand(&mut prng);
let alpha = (t.y - q.y) / (t.x - q.x);
// -bias
let bias_minus = alpha * t.x - t.y;

let x = alpha.square() - t.x - q.x;
let y = bias_minus - alpha * x;
let r = (t + q).into_affine();

let (hinted_check_add, hints) = G1Affine::hinted_check_add(t, q);
let (hinted_check_add, hints) = G1Affine::hinted_check_add_prevent_degenerate(t, q);

let script = script! {
for hint in hints {
{ hint.push() }
}
{ Fq::push(t.x) }
{ Fq::push(t.y) }
{ Fq::push(q.x) }
{ Fq::push(q.y) }
{ G1Affine::push(t) }
{ G1Affine::push(q) }
{ hinted_check_add.clone() }
// [x']
{ Fq::push(y) }
// [x', y', y]
{ Fq::equalverify(1,0) }
// [x']
{ Fq::push(x) }
// [x', x]
{ Fq::equalverify(1,0) }
// []
{ G1Affine::push(r) }
{ G1Affine::equalverify() }
OP_TRUE
// [OP_TRUE]
};
let exec_result = execute_script(script);
assert!(exec_result.success);
println!(
"hinted_check_add: {} @ {} stack",
"hinted_check_add_prevent_degenerate: {} @ {} stack",
hinted_check_add.len(),
exec_result.stats.max_nb_stack_items
);
}

#[test]
fn test_g1_affine_hinted_check_add() {
let mut prng = ChaCha20Rng::seed_from_u64(0);
let t = ark_bn254::G1Affine::rand(&mut prng);
let q = ark_bn254::G1Affine::rand(&mut prng);
let r = (t + q).into_affine();
let tt = (t + t).into_affine();
let negt = -t;
let z = ark_bn254::G1Affine::zero();

for (t, q, r) in [(t, q, r), (t, t, tt), (t, negt, z), (t, z, t)] {
let (hinted_check_add, hints) = G1Affine::hinted_check_add(t, q);

let script = script! {
for hint in hints {
{ hint.push() }
}
{ G1Affine::push(t) }
{ G1Affine::push(q) }
{ hinted_check_add.clone() }
{ G1Affine::push(r) }
{ G1Affine::equalverify() }
OP_TRUE
};
let exec_result = execute_script(script);
assert!(exec_result.success);
println!(
"hinted_check_add: {} @ {} stack",
hinted_check_add.len(),
exec_result.stats.max_nb_stack_items
);
}
}

#[test]
fn test_g1_affine_hinted_check_double() {
//println!("G1.hinted_add: {} bytes", G1Affine::check_add().len());
Expand Down
2 changes: 1 addition & 1 deletion bitvm/src/bn254/msm.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -230,7 +230,7 @@ fn accumulate_addition_chain_for_a_scalar_mul(
);

// accumulate value using hinted_check_add
let (add_scr, add_hints) = G1Affine::hinted_check_add(prev, row_g1);
let (add_scr, add_hints) = G1Affine::hinted_check_add_prevent_degenerate(prev, row_g1);

prev = (prev + row_g1).into_affine(); // output of this chunk: t + q
vec_row_g1_scr.push(row_g1_scr);
Expand Down
2 changes: 1 addition & 1 deletion bitvm/src/chunk/taps_msm.rs
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Expand Up @@ -135,7 +135,7 @@ pub(crate) fn chunk_hash_p(
let (tx, qx, ty, qy) = (hint_in_t.x, hint_in_q.x, hint_in_t.y, hint_in_q.y);
let t = ark_bn254::G1Affine::new_unchecked(tx, ty);
let q = ark_bn254::G1Affine::new_unchecked(qx, qy);
let (add_scr, add_hints) = G1Affine::hinted_check_add(t, q);
let (add_scr, add_hints) = G1Affine::hinted_check_add_prevent_degenerate(t, q);
let r = (t + q).into_affine();
let ops_script = script! {
// [t] [hash_r, hash_t]
Expand Down