Keccak256 blackbox instruction injectivity test fails

[michaeljklein]

Aim

Attempted to test that the Keccak256 blackbox instruction is injective as part of #5614

Expected Behavior

Expected to find that solving the Keccak256 blackbox function on different inputs resolves to different outputs, i.e.

forall x, y. x != y -> f x != f y

Bug

The following test passes:

#[test]
fn keccak256_injective_regression() {
    // 2⁸×61916068613087029720904767285796661
    let x = FieldElement::from(15850513564950279608551620425163945216u128);

    // 2⁸×220343640628484768581538005104492351
    let y = FieldElement::from(56407972000892100756873729306750041856u128);
    assert!(x != y);

    let inputs = vec![(x, false)];
    let distinct_inputs = vec![(y, false)];
    let num_outputs = 32;

    assert_eq!(
        solve_array_input_blackbox_call(inputs, num_outputs, keccak256_op),
        solve_array_input_blackbox_call(distinct_inputs, num_outputs, keccak256_op));

    assert!(result, "{}", message);
}

To Reproduce

Workaround

None

Workaround Description

No response

Additional Context

No response

Project Impact

None

Blocker Context

No response

Nargo Version

No response

NoirJS Version

No response

Proving Backend Tooling & Version

No response

Would you like to submit a PR for this Issue?

None

Support Needs

No response

[michaeljklein]

I am still looking into this, but @vezenovm suggested that keccak256 could silently require the num_bits of the FunctionInput to be 8.

[TomAFrench]

Closing as we no longer have a keccak256 opcode