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Add size checking to multiscalar multiplication.

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This commit is contained in:
Henry de Valence 2017-07-30 23:54:13 -07:00
parent 2d01aa1bf7
commit 720da348c0
2 changed files with 59 additions and 14 deletions
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49
src/curve.rs
View file

@ -944,12 +944,15 @@ impl<'a, 'b> Mul<&'b ExtendedPoint> for &'a Scalar {
#[cfg(any(feature = "alloc", feature = "std"))]
pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> ExtendedPoint
where I: IntoIterator<Item = &'a Scalar>,
J: IntoIterator<Item = &'b ExtendedPoint>
I::IntoIter: ExactSizeIterator,
J: IntoIterator<Item = &'b ExtendedPoint>,
J::IntoIter: ExactSizeIterator,
{
//assert_eq!(scalars.len(), points.len());
let scalars_iter = scalars.into_iter();
let points_iter = points.into_iter();
assert_eq!(scalars_iter.len(), points_iter.len());
let lookup_tables: Vec<_> = points.into_iter()
.map(|P_i| {
let lookup_tables: Vec<_> = points_iter.map(|P_i| {
// Construct a lookup table of [P_i,2*P_i,3*P_i,4*P_i,5*P_i,6*P_i,7*P_i]
let mut lookup_table = [P_i.to_projective_niels(); 8];
for j in 0..7 {
@ -964,8 +967,7 @@ pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> ExtendedPoint
// s_i = s_{i,0} + s_{i,1}*16^1 + ... + s_{i,63}*16^63,
//
// with `-8 ≤ s_{i,j} < 8` for `0 ≤ j < 63` and `-8 ≤ s_{i,63} ≤ 8`.
let scalar_digits_list: Vec<_> = scalars.into_iter()
.map(|c| c.to_radix_16()).collect();
let scalar_digits_list: Vec<_> = scalars_iter.map(|c| c.to_radix_16()).collect();
// Compute s_1*P_1 + ... + s_n*P_n: since
//
@ -1283,15 +1285,18 @@ pub mod vartime {
/// error to call this function with two vectors of different lengths.
#[cfg(any(feature = "alloc", feature = "std"))]
pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> ExtendedPoint
where I: IntoIterator<Item = &'a Scalar>,
J: IntoIterator<Item = &'b ExtendedPoint>
where
I: IntoIterator<Item = &'a Scalar>,
I::IntoIter: ExactSizeIterator,
J: IntoIterator<Item = &'b ExtendedPoint>,
J::IntoIter: ExactSizeIterator,
{
//assert_eq!(scalars.len(), points.len());
let scalars_iter = scalars.into_iter();
let points_iter = points.into_iter();
assert_eq!(scalars_iter.len(), points_iter.len());
let nafs: Vec<_> = scalars.into_iter()
.map(|c| c.non_adjacent_form()).collect();
let odd_multiples: Vec<_> = points.into_iter()
.map(|P| OddMultiples::create(P)).collect();
let nafs: Vec<_> = scalars_iter.map(|c| c.non_adjacent_form()).collect();
let odd_multiples: Vec<_> = points_iter.map(|P| OddMultiples::create(P)).collect();
let mut r = ProjectivePoint::identity();
@ -1701,6 +1706,15 @@ mod test {
assert!(P1.compress().as_bytes() == P2.compress().as_bytes());
}
#[test]
#[should_panic]
fn multiscalar_mult_with_wrong_sized_arguments() {
let result = multiscalar_mult(
&[A_SCALAR, B_SCALAR],
&[constants::ED25519_BASEPOINT],
);
}
mod vartime {
use super::super::*;
use super::{A_SCALAR, B_SCALAR, A_TIMES_BASEPOINT, DOUBLE_SCALAR_MULT_RESULT};
@ -1713,6 +1727,15 @@ mod test {
assert_eq!(result.compress_edwards(), DOUBLE_SCALAR_MULT_RESULT);
}
#[test]
#[should_panic]
fn multiscalar_mult_with_wrong_sized_arguments() {
let result = vartime::multiscalar_mult(
&[A_SCALAR, B_SCALAR],
&[constants::ED25519_BASEPOINT],
);
}
#[test]
fn multiscalar_mult_vs_ed25519py() {
let A = A_TIMES_BASEPOINT.decompress().unwrap();

24
src/decaf.rs
View file

@ -577,6 +577,26 @@ impl<'a, 'b> Mul<&'b DecafPoint> for &'a Scalar {
}
}
/// Given a vector of (possibly secret) scalars and a vector of
/// (possibly secret) points, compute `c_1 P_1 + ... + c_n P_n`.
///
/// This function has the same behaviour as
/// `vartime::multiscalar_mult` but is constant-time.
///
/// # Input
///
/// A vector of `Scalar`s and a vector of `DecafPoints`. It is an
/// error to call this function with two vectors of different lengths.
#[cfg(any(feature = "alloc", feature = "std"))]
pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> DecafPoint
where I: IntoIterator<Item = &'a Scalar>,
I::IntoIter: ExactSizeIterator,
J: IntoIterator<Item = &'b DecafPoint>,
J::IntoIter: ExactSizeIterator,
{
let extended_points = points.into_iter().map(|P| &P.0);
DecafPoint(curve::multiscalar_mult(scalars, extended_points))
}
/// Precomputation
#[derive(Clone)]
@ -685,7 +705,9 @@ pub mod vartime {
/// error to call this function with two vectors of different lengths.
pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> DecafPoint
where I: IntoIterator<Item = &'a Scalar>,
J: IntoIterator<Item = &'b DecafPoint>
I::IntoIter: ExactSizeIterator,
J: IntoIterator<Item = &'b DecafPoint>,
J::IntoIter: ExactSizeIterator,
{
let extended_points = points.into_iter().map(|P| &P.0);
DecafPoint(curve::vartime::multiscalar_mult(scalars, extended_points))