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PeerDAS: Check for degree overflow in multiply_polynomialcoeff()
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asn-d6 committed Mar 8, 2024
1 parent 1a33bf8 commit c71fb00
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3 changes: 3 additions & 0 deletions specs/_features/eip7594/polynomial-commitments-sampling.md
Original file line number Diff line number Diff line change
Expand Up @@ -196,12 +196,15 @@ def multiply_polynomialcoeff(a: PolynomialCoeff, b: PolynomialCoeff) -> Polynomi
"""
Multiplies the coefficient form polynomials ``a`` and ``b``
"""
assert len(a) + len(b) <= FIELD_ELEMENTS_PER_EXT_BLOB

r = [0]
for power, coef in enumerate(a):
summand = [0] * power + [int(coef) * int(x) % BLS_MODULUS for x in b]
r = add_polynomialcoeff(r, summand)
return r
```

#### `divide_polynomialcoeff`

```python
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Expand Up @@ -2,6 +2,7 @@
from eth2spec.test.context import (
spec_test,
single_phase,
expect_assertion_error,
with_eip7594_and_later,
)
from eth2spec.test.helpers.sharding import (
Expand Down Expand Up @@ -105,3 +106,19 @@ def test_recover_polynomial(spec):
# Now flatten the cells and check that they match the entirety of the recovered data
flattened_cells = [x for xs in cells for x in xs]
assert flattened_cells == recovered_data


@with_eip7594_and_later
@spec_test
@single_phase
def test_multiply_polynomial_degree_overflow(spec):
rng = random.Random(5566)

# Perform a legitimate-but-maxed-out polynomial multiplication
poly1_coeff = [rng.randint(0, BLS_MODULUS - 1) for _ in range(spec.FIELD_ELEMENTS_PER_BLOB)]
poly2_coeff = [rng.randint(0, BLS_MODULUS - 1) for _ in range(spec.FIELD_ELEMENTS_PER_BLOB)]
_ = spec.multiply_polynomialcoeff(poly1_coeff, poly2_coeff)

# Now overflow the degree by pumping the degree of one of the inputs by one
poly2_coeff = [rng.randint(0, BLS_MODULUS - 1) for _ in range(spec.FIELD_ELEMENTS_PER_BLOB + 1)]
expect_assertion_error(lambda: spec.multiply_polynomialcoeff(poly1_coeff, poly2_coeff))

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