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Rename CompressedPoint -> CompressedEdwardsY

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This allows other compression formats (e.g., CompressedMontgomeryX).
This commit is contained in:
Henry de Valence 2016-12-23 17:50:24 -08:00
parent 42c2578f4c
commit d1599410ee
1 changed files with 37 additions and 36 deletions
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73
src/curve.rs
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@ -91,33 +91,34 @@ use util::bytes_equal_ct;
// Compressed points
// ------------------------------------------------------------------------
/// An affine point `(x,y)` on the curve is determined by the
/// `y`-coordinate and the sign of `x`, marshalled into a 32-byte array.
/// In "Edwards y" format, the point `(x,y)` on the curve is
/// determined by the `y`-coordinate and the sign of `x`, marshalled
/// into a 32-byte array.
///
/// The first 255 bits of a CompressedPoint represent the
/// The first 255 bits of a CompressedEdwardsY represent the
/// y-coordinate. The high bit of the 32nd byte gives the sign of `x`.
#[derive(Copy, Clone)]
pub struct CompressedPoint(pub [u8; 32]);
pub struct CompressedEdwardsY(pub [u8; 32]);
impl Debug for CompressedPoint {
impl Debug for CompressedEdwardsY {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "CompressedPoint: {:?}", &self.0[..])
write!(f, "CompressedEdwardsY: {:?}", &self.0[..])
}
}
impl Eq for CompressedPoint {}
impl PartialEq for CompressedPoint {
/// Determine if this `CompressedPoint` is equal to another.
impl Eq for CompressedEdwardsY {}
impl PartialEq for CompressedEdwardsY {
/// Determine if this `CompressedEdwardsY` is equal to another.
///
/// # Warning
///
/// This function is NOT constant time.
fn eq(&self, other: &CompressedPoint) -> bool {
fn eq(&self, other: &CompressedEdwardsY) -> bool {
return self.0 == other.0;
}
}
impl Index<usize> for CompressedPoint {
impl Index<usize> for CompressedEdwardsY {
type Output = u8;
fn index<'a>(&'a self, _index: usize) -> &'a u8 {
@ -126,8 +127,8 @@ impl Index<usize> for CompressedPoint {
}
}
impl CompressedPoint {
/// View this `CompressedPoint` as an array of bytes.
impl CompressedEdwardsY {
/// View this `CompressedEdwardsY` as an array of bytes.
pub fn to_bytes(&self) -> [u8;32] {
self.0
}
@ -332,8 +333,8 @@ impl ProjectivePoint {
}
}
/// Convert this point to a `CompressedPoint`
pub fn compress(&self) -> CompressedPoint {
/// Convert this point to a `CompressedEdwardsY`
pub fn compress(&self) -> CompressedEdwardsY {
let recip = self.Z.invert();
let x = &self.X * &recip;
let y = &self.Y * &recip;
@ -341,7 +342,7 @@ impl ProjectivePoint {
s = y.to_bytes();
s[31] ^= (x.is_negative() << 7) as u8;
CompressedPoint(s)
CompressedEdwardsY(s)
}
}
@ -368,8 +369,8 @@ impl ExtendedPoint {
}
}
/// Convert this point to a `CompressedPoint`
pub fn compress(&self) -> CompressedPoint {
/// Compress this point to `CompressedEdwardsY` format
pub fn compress(&self) -> CompressedEdwardsY {
self.to_projective().compress()
}
}
@ -814,11 +815,11 @@ mod test {
///
/// Generated with Sage: these are the bytes of 4/5 in 𝔽_p. The
/// sign bit is 0 since the basepoint has x chosen to be positive.
static BASE_CMPRSSD: CompressedPoint =
CompressedPoint([0x58, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66]);
static BASE_CMPRSSD: CompressedEdwardsY =
CompressedEdwardsY([0x58, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66]);
/// X coordinate of the basepoint.
/// = 15112221349535400772501151409588531511454012693041857206046113283949847762202
@ -826,17 +827,17 @@ mod test {
[0x1a, 0xd5, 0x25, 0x8f, 0x60, 0x2d, 0x56, 0xc9, 0xb2, 0xa7, 0x25, 0x95, 0x60, 0xc7, 0x2c, 0x69,
0x5c, 0xdc, 0xd6, 0xfd, 0x31, 0xe2, 0xa4, 0xc0, 0xfe, 0x53, 0x6e, 0xcd, 0xd3, 0x36, 0x69, 0x21];
static BASE2_CMPRSSD: CompressedPoint =
CompressedPoint([0xc9, 0xa3, 0xf8, 0x6a, 0xae, 0x46, 0x5f, 0xe,
0x56, 0x51, 0x38, 0x64, 0x51, 0x0f, 0x39, 0x97,
0x56, 0x1f, 0xa2, 0xc9, 0xe8, 0x5e, 0xa2, 0x1d,
0xc2, 0x29, 0x23, 0x09, 0xf3, 0xcd, 0x60, 0x22]);
static BASE2_CMPRSSD: CompressedEdwardsY =
CompressedEdwardsY([0xc9, 0xa3, 0xf8, 0x6a, 0xae, 0x46, 0x5f, 0xe,
0x56, 0x51, 0x38, 0x64, 0x51, 0x0f, 0x39, 0x97,
0x56, 0x1f, 0xa2, 0xc9, 0xe8, 0x5e, 0xa2, 0x1d,
0xc2, 0x29, 0x23, 0x09, 0xf3, 0xcd, 0x60, 0x22]);
static BASE16_CMPRSSD: CompressedPoint =
CompressedPoint([0xeb, 0x27, 0x67, 0xc1, 0x37, 0xab, 0x7a, 0xd8,
0x27, 0x9c, 0x07, 0x8e, 0xff, 0x11, 0x6a, 0xb0,
0x78, 0x6e, 0xad, 0x3a, 0x2e, 0x0f, 0x98, 0x9f,
0x72, 0xc3, 0x7f, 0x82, 0xf2, 0x96, 0x96, 0x70]);
static BASE16_CMPRSSD: CompressedEdwardsY =
CompressedEdwardsY([0xeb, 0x27, 0x67, 0xc1, 0x37, 0xab, 0x7a, 0xd8,
0x27, 0x9c, 0x07, 0x8e, 0xff, 0x11, 0x6a, 0xb0,
0x78, 0x6e, 0xad, 0x3a, 0x2e, 0x0f, 0x98, 0x9f,
0x72, 0xc3, 0x7f, 0x82, 0xf2, 0x96, 0x96, 0x70]);
/// 4493907448824000747700850167940867464579944529806937181821189941592931634714
static A_SCALAR: Scalar = Scalar([
@ -853,14 +854,14 @@ mod test {
0x56, 0xa7, 0xd4, 0xaa, 0xb8, 0x60, 0x8a, 0x05]);
/// A_SCALAR * basepoint, computed with ed25519.py
static A_TIMES_BASEPOINT: CompressedPoint = CompressedPoint([
static A_TIMES_BASEPOINT: CompressedEdwardsY = CompressedEdwardsY([
0xea, 0x27, 0xe2, 0x60, 0x53, 0xdf, 0x1b, 0x59,
0x56, 0xf1, 0x4d, 0x5d, 0xec, 0x3c, 0x34, 0xc3,
0x84, 0xa2, 0x69, 0xb7, 0x4c, 0xc3, 0x80, 0x3e,
0xa8, 0xe2, 0xe7, 0xc9, 0x42, 0x5e, 0x40, 0xa5]);
/// A_SCALAR * (A_TIMES_BASEPOINT) + B_SCALAR * BASEPOINT
static DOUBLE_SCALAR_MULT_RESULT: CompressedPoint = CompressedPoint([
static DOUBLE_SCALAR_MULT_RESULT: CompressedEdwardsY = CompressedEdwardsY([
0x7d, 0xfd, 0x6c, 0x45, 0xaf, 0x6d, 0x6e, 0x0e,
0xba, 0x20, 0x37, 0x1a, 0x23, 0x64, 0x59, 0xc4,
0xc0, 0x46, 0x83, 0x43, 0xde, 0x70, 0x4b, 0x85,
@ -886,7 +887,7 @@ mod test {
let mut m_bp_bytes: [u8;32] = BASE_CMPRSSD.to_bytes().clone();
// Set the high bit of the last byte to flip the sign
m_bp_bytes[31] |= 1 << 7;
let m_bp = CompressedPoint(m_bp_bytes).decompress().unwrap();
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);