Add BoxedUint::inv_mod
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Support for computing modular inverses, proptested against the
implementation in `num-bigint-dig`, which this commit also switches to
(`num-bigint` doesn't provide an implementation we can test against).
Uses the same method as `Uint::inv_mod`, namely an algorithm equivalent
to GMP's `mpn_sec_invert`, with code largely duplicated from the `Uint`
version.
Notably this version is variable time with respect to the modulus,
which might be avoidable with alternative implementations, such as
Bernstein-Yang.
It would also be nice to deduplicate the implementation, though reuse
between `const fn` use cases and heap-backed use cases is difficult.
This additionally adds the following prerequisites:
- `BoxedUint::{conditional_assign, conditional_swap, is_one}
- `BoxedUint::conditional_wrapping_*` (private)
- `BoxedUint::{trailing_zeros, wrapping_mul, neg}`
- `BoxedUint::{shl, shr}`
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Support for computing modular inverses, proptested against the implementation in
num-bigint-dig, which this commit also switches to (num-bigintdoesn't provide an implementation we can test against).Uses the same method as
Uint::inv_mod, namely an algorithm equivalent to GMP'smpn_sec_invert, with code largely duplicated from theUintversion.Notably this version is variable time with respect to the modulus, which might be avoidable with alternative implementations, such as Bernstein-Yang.
It would also be nice to deduplicate the implementation, though reuse between
const fnuse cases and heap-backed use cases is difficult.This additionally adds the following prerequisites:
BoxedUint::conditional_wrapping_*(private)BoxedUint::{trailing_zeros, wrapping_mul, neg}BoxedUint::{shl, shr}