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Check xy is nonnegative, y nonzero in decoding.

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Henry de Valence 2017-02-21 12:33:57 -08:00
parent 5daa217b18
commit 95bf09a335
1 changed files with 10 additions and 1 deletions
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11
src/decaf.rs
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@ -83,7 +83,16 @@ impl CompressedDecaf {
let Y = &w * &Z;
let T = &w * &X;
Some(DecafPoint(ExtendedPoint{ X: X, Y: Y, Z: Z, T: T }))
// "To decode the point, one must decode it to affine form
// instead of projective, and check that xy is non-negative."
//
// XXX can we merge this inversion with the one above?
let xy = &T * &Z.invert();
if (Y.is_nonzero() & xy.is_nonnegative_decaf()) == 1u8 {
Some(DecafPoint(ExtendedPoint{ X: X, Y: Y, Z: Z, T: T }))
} else {
None
}
}
}