Noble-ed25519, does not handle the point at infinity in the toAffine method #99
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paulmillr
reviewed
Feb 19, 2024
| @@ -99,7 +99,7 @@ class Point { // Point in xyzt extende | |||
| } | |||
| toAffine(): AffinePoint { // converts point to 2d xy affine point | |||
| const { ex: x, ey: y, ez: z } = this; // (x, y, z, t) ∋ (x=x/z, y=y/z, t=xy) | |||
| if (this.is0()) return { x: 0n, y: 0n }; // fast-path for zero point | |||
| if (this.equals(I)) return { x: 0n, y: 1n }; // fast-path for zero point | |||
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why is0 replaced with equals i?
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In the current implementation of the
toAffinemethod within the@noble-ed25519library, there is an incorrect handling of the point at infinity O when transforming from projective to affine coordinates. Specifically, the point at infinity is incorrectly encoded as(0, 0)for the ed25519 curve.However, for the ed25519 curve, the point at infinity should be represented by (0, 1) in affine coordinates to satisfy the curve equation and ensure correct computations during export and import operations.
We can fix it by doing this :
Solved with @Elli610