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Add field arithmetic skeleton #7

Merged
merged 3 commits into from
Apr 9, 2019
Merged

Add field arithmetic skeleton #7

merged 3 commits into from
Apr 9, 2019

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hdevalence
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This doesn't yet fill in the implementations, so it won't run, but it means that it's possible to start using the api with cargo check. Progress on #1 to unblock other issues.

This defines (but does not implement):

* conversion to and from the curve25519-dalek packed `Scalar` type;
* addition;
* subtraction;
* multiplication;
* zero & one constructors and Default;
* inversion;

The implementation in curve25519-dalek allows doing operations either in
Montgomery form or not in Montgomery form; I think that for this use-case, it
would be better to require that a `FieldElement` is *always* in Montgomery
form, so that the multiplication is always Montgomery multiplication.  We can
also probably save some time by allowing the representatives to lie in the
range [0, 2*l) instead of [0, l) as in the original implementation (cf. "Montgomery
Multiplication Needs No Final Subtractions").
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@cathieyun cathieyun left a comment

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LGTM!

@hdevalence hdevalence merged commit ce61dd1 into master Apr 9, 2019
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2 participants