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Clean decompression_sign_handling

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This commit is contained in:
Henry de Valence 2017-03-07 00:11:47 -08:00
parent b5b0ac7628
commit 94416eb1cb
1 changed files with 11 additions and 13 deletions
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24
src/curve.rs
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@ -1119,29 +1119,27 @@ mod test {
fn basepoint_decompression_compression() {
let base_X = FieldElement::from_bytes(&BASE_X_COORD_BYTES);
let bp = BASE_CMPRSSD.decompress().unwrap();
let bp2 = BASE2_CMPRSSD.decompress().unwrap();
assert!( bp.is_valid());
assert!(bp2.is_valid());
let compressed = bp.compress();
let compressed2 = bp2.compress();
// Check that decompression actually gives the correct X coordinate
assert_eq!(base_X, bp.X);
assert_eq!(compressed, BASE_CMPRSSD);
assert_eq!(compressed2, BASE2_CMPRSSD);
}
/// Test sign handling in decompression
#[test]
fn decompression_sign_handling() {
let mut m_bp_bytes: [u8;32] = BASE_CMPRSSD.as_bytes().clone();
// Set the high bit of the last byte to flip the sign
m_bp_bytes[31] |= 1 << 7;
let m_bp = CompressedEdwardsY(m_bp_bytes).decompress().unwrap();
let bp = BASE_CMPRSSD.decompress().unwrap();
assert_eq!(m_bp.X, -(&bp.X));
assert_eq!(m_bp.Y, bp.Y);
assert_eq!(m_bp.Z, bp.Z);
assert_eq!(m_bp.T, -(&bp.T));
// Manually set the high bit of the last byte to flip the sign
let mut minus_basepoint_bytes = BASE_CMPRSSD.as_bytes().clone();
minus_basepoint_bytes[31] |= 1 << 7;
let minus_basepoint = CompressedEdwardsY(minus_basepoint_bytes)
.decompress().unwrap();
// Test projective coordinates exactly since we know they should
// only differ by a flipped sign.
assert_eq!(minus_basepoint.X, -(&constants::BASEPOINT.X));
assert_eq!(minus_basepoint.Y, constants::BASEPOINT.Y);
assert_eq!(minus_basepoint.Z, constants::BASEPOINT.Z);
assert_eq!(minus_basepoint.T, -(&constants::BASEPOINT.T));
}
/// Test that computing 1*basepoint gives the correct basepoint.