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Fix to_bytes() for ProjectivePoint::identity() #443

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Merged
tarcieri merged 2 commits into from
Sep 30, 2021
Merged

Fix to_bytes() for ProjectivePoint::identity() #443

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b3bb218
Fix `to_bytes()` for `ProjectivePoint::identity()`
daxpedda Sep 30, 2021
0ba5440
Add a note explaining the test
daxpedda Sep 30, 2021
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14 changes: 12 additions & 2 deletions p256/src/arithmetic/projective.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,11 @@ impl GroupEncoding for ProjectivePoint {
}

fn to_bytes(&self) -> Self::Repr {
CompressedPoint::clone_from_slice(self.to_affine().to_encoded_point(true).as_bytes())
let bytes = self.to_affine().to_encoded_point(true);
let bytes = bytes.as_bytes();
let mut result = CompressedPoint::default();
result[..bytes.len()].copy_from_slice(bytes);
result
}
}

Expand Down Expand Up @@ -521,7 +525,7 @@ impl<'a> Neg for &'a ProjectivePoint {
mod tests {
use super::{AffinePoint, ProjectivePoint, Scalar};
use crate::test_vectors::group::{ADD_TEST_VECTORS, MUL_TEST_VECTORS};
use elliptic_curve::group::{ff::PrimeField, prime::PrimeCurveAffine};
use elliptic_curve::group::{ff::PrimeField, prime::PrimeCurveAffine, GroupEncoding};

#[test]
fn affine_to_projective() {
Expand Down Expand Up @@ -665,4 +669,10 @@ mod tests {
assert_eq!(res.y.to_bytes(), coords.1.into());
}
}

#[test]
fn projective_identity_to_bytes() {
// This is technically an invalid SEC1 encoding, but is preferable to panicking.
assert_eq!([0; 33], ProjectivePoint::identity().to_bytes().as_slice());
}
}