# conditional-hash-range

> Conditional unsigned subtraction reaches a fixed-width native persistent-hash input without a qualified inactive-case range invariant.

Canonical: https://nightshade.dicksonwu.xyz/rules/conditional-hash-range.html
Release: Nightshade 0.1.1 (v0.1.1)

| Field | Value |
| --- | --- |
| Rule ID | `conditional-hash-range` |
| Severity | low |
| Confidence | low |
| Maturity | experimental |
| Selection | Opt-in |
| Policy intent | not required |
| Default enabled | no |
| Category | Other active opt-ins / Privacy and cryptographic derivations |
| Engine facts used | resolved-source-references, resolved-types, canonical-native-calls |
| Release | v0.1.1 |

## Selection and scope

Not selected by default. Select it with `--detectors` or the `detectors` list in nightshade.json. Either one replaces profile selection, so list every rule you want.

```sh
./.nightshade/node_modules/.bin/nightshade ./contracts --detectors conditional-hash-range
./.nightshade/node_modules/.bin/nightshade detector show conditional-hash-range
```

The first command runs only this rule; `--detectors` takes a comma-separated list. The second prints the rule's metadata from your installed version.

Severity is review priority. It does not express exploitability or impact. Confidence is detector metadata, not a probability. All built-in rules are experimental.

Compiler scope: the engine supports the pinned profiles 0.28.0, 0.29.0, 0.30.0, 0.31.1, 0.33.0-rc.2, 0.34.0, 0.35.0-rc.1 and 0.35.0, with ZKIR2 by default. Support for this rule can be narrower; the rule documentation below states any narrower scope.

## Corpus checks

Synthetic corpus checks for this rule in the 0.1.1 proof run. A check counts only with compiler acceptance and complete analysis.

| Positive detected | Corrected quiet | Lookalike quiet | Other negative quiet | Incomplete |
| ---: | ---: | ---: | ---: | ---: |
| 1/1 | 1/1 | 1/1 | 0/0 | 0 |

No deviations were recorded for this rule.

These are behavior checks on synthetic fixtures, not a precision or recall estimate. See [evaluation](https://nightshade.dicksonwu.xyz/evaluation.md#synthetic-corpus).

## Rule documentation

From https://github.com/DicksonWu654/nightshade/blob/v0.1.1/docs/detectors/conditional-hash-range.md at v0.1.1.

Availability: **opt-in compiler compatibility review**, no policy required.
Severity/confidence: **low/high**. Select with
`--detectors conditional-hash-range`.

A conditional unsigned subtraction can feed a fixed-width native hash input while
its underflow assertion is guarded. In the qualified **Compact0.34.0/ZKIR2**
output, a direct `Uint<128>` subtraction feeds `persistentHash<Uint<128>>`'s
16-byte input without selecting safe operands when the source branch is inactive.
The generated JavaScript keeps the computation inside the source branch; this
rule does not describe that JavaScript as executing the inactive hash.

```compact
import CompactStandardLibrary;
export ledger digest: Bytes<32>;
export circuit update(enabled: Boolean, a: Uint<128>, b: Uint<128>): [] {
  if (disclose(enabled)) {
    const difference = (a - b) as Uint<128>;
    digest = disclose(persistentHash<Uint<128>>(difference));
  }
}
```

The finding identifies the subtraction, native hash input and controlling source
branch. It is a static review relationship, **not proof of an invalid input,
proof failure, runtime rejection or deployed vulnerability**. Earlier surviving
unconditional ordering evidence and qualified safe inactive operand selections
are quiet controls. A check inside the same conditional establishes only its
active-case constraint.

Select safe operands using the actual controlling condition before computing the
hash preimage, and preserve intended active validation. Merely guarding the ledger
assignment does not supply an inactive-case hash range invariant. Inspect the
project's generated compiler output before relying on version-specific behavior.
A direct hash of an already constrained `Uint<128>` input is a quiet lookalike.

## Suppress a match

If a match is intentional, suppress it on the line before with the exact rule ID and a reason of at least eight characters:

```compact
// nightshade-disable-next-line conditional-hash-range -- Reason this match is intentional
```

Diagnostics cannot be suppressed, and an unmatched directive for a selected rule makes analysis incomplete. See [configuration](https://nightshade.dicksonwu.xyz/configuration.md#suppress-an-intentional-match) for fingerprint suppressions and baselines.

## References

- [Rule source document at v0.1.1](https://github.com/DicksonWu654/nightshade/blob/v0.1.1/docs/detectors/conditional-hash-range.md)
- [Catalog entry in rules.json](https://nightshade.dicksonwu.xyz/rules.json)
- [All rules](https://nightshade.dicksonwu.xyz/rules.md#privacy-and-cryptographic-derivations)
- [Limitations](https://nightshade.dicksonwu.xyz/limitations.md)