crypto.edwards25519: optimize rejectLowOrder #30650

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jedisct1 merged 1 commit from jedisct1/zig:ed25519rej into master 2026-01-02 23:37:14 +01:00

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jedisct1 commented 2026-01-02 00:05:19 +01:00

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Reject low-order points by checking projective coordinates directly instead of using affine coordinates.

Equivalent, but saves CPU cycles (~254 field multiplications total before, 3 field multiplications after).

Reject low-order points by checking projective coordinates directly instead of using affine coordinates. Equivalent, but saves CPU cycles (~254 field multiplications total before, 3 field multiplications after).

jedisct1 added 1 commit 2026-01-02 00:05:23 +01:00

crypto.edwards25519: optimize rejectLowOrder ... 1baa127c65

Reject low-order points by checking projective coordinates directly
instead of using affine coordinates.

Equivalent, but saves CPU cycles (~254 field multiplications total
before, 3 field multiplications after).

sinon commented 2026-01-02 00:16:39 +01:00

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Another thing I suggest, that I'm not sure the stdlib needs but still, is an API for rejecting low-order (order <= 8) points from a known affine point. Very useful for rejecting low-order points (like A,R in EdDSA verify) when it was just decoded from the wire, so you know it's affine. It's only 4 comparisons: example impl.

Another thing I suggest, that I'm not sure the stdlib needs but still, is an API for rejecting low-order (order <= 8) points from a known affine point. Very useful for rejecting low-order points (like A,R in EdDSA verify) when it was just decoded from the wire, so you know it's affine. It's only 4 comparisons: [example impl](https://github.com/Syndica/sig/blob/a1f9f3223c3e192d1c431eccd3fbfb507c7abe1d/src/crypto/ed25519/lib.zig#L156).

jedisct1 commented 2026-01-02 23:37:05 +01:00

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@sinon why not, that can be useful!

@sinon why not, that can be useful!

jedisct1 merged commit 1bf29757d9 into master 2026-01-02 23:37:14 +01:00

jedisct1 deleted branch ed25519rej 2026-01-02 23:37:16 +01:00

jedisct1 referenced this pull request from a commit 2026-01-02 23:37:16 +01:00

Merge pull request 'crypto.edwards25519: optimize rejectLowOrder' (#30650) from jedisct1/zig:ed25519rej into master

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