Have PrimeField::from_repr borrow its input#137
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tarcieri wants to merge 1 commit intozkcrypto:release-0.14.0from
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Have PrimeField::from_repr borrow its input#137tarcieri wants to merge 1 commit intozkcrypto:release-0.14.0from
PrimeField::from_repr borrow its input#137tarcieri wants to merge 1 commit intozkcrypto:release-0.14.0from
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From the API guidelines, a function that does not require ownership should borrow its input: https://rust-lang.github.io/api-guidelines/flexibility.html?highlight=clone#caller-decides-where-to-copy-and-place-data-c-caller-control In general, I think there's an intermediate decoding step between `PrimeField::Repr` and the corresponding `Self` type which receives an impl thereof, rather than the `Self` type actually taking ownership of the `Repr` data. Since field element types sometimes represent secrets, taking ownership of the data means the caller can't zeroize that data, and moving the data rather than borrowing it may introduce an additional copy.
This was referenced May 29, 2025
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I did the update work for the RustCrypto crates here: |
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Note that the existing bounds somewhat complicate cases where you want to do |
tarcieri
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This viral bound came because `PrimeField::from_repr` expects a value rather than a reference, and previously it was using `Copy` to do the conversion. However, `Clone` is available unconditionally avoiding the need for such bounds. Ultimately `PrimeField::from_repr` should probably borrow its input. See: zkcrypto/ff#137 This came up implementing wNAF since `ProjectivePoint::wnaf` previously needed it, so if we use it for `mul_vartime` it ultimately adds viral bounds that it would be nice to avoid.
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From the API guidelines, a function that does not require ownership should borrow its input:
https://rust-lang.github.io/api-guidelines/flexibility.html?highlight=clone#caller-decides-where-to-copy-and-place-data-c-caller-control
In general, I think there's an intermediate decoding step between
PrimeField::Reprand the correspondingSelftype which receives an impl thereof, rather than theSelftype actually taking ownership of theReprdata.Since field element types sometimes represent secrets, taking ownership of the data means the caller can't zeroize that data, and moving the data rather than borrowing it may introduce an additional copy.