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Remove potentially vartime (due to cache side-channel attacks) table access in dalek-ff-group and minimal-ed448

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This commit is contained in:
Luke Parker
2024-10-27 08:51:19 -04:00
parent f3d20e60b3
commit d0201cf2e5
5 changed files with 41 additions and 5 deletions
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11
crypto/dalek-ff-group/src/field.rs
View File

@@ -244,7 +244,16 @@ impl FieldElement {
res *= res;
}
}
res *= table[usize::from(bits)];
let mut scale_by = FieldElement::ONE;
#[allow(clippy::needless_range_loop)]
for i in 0 .. 16 {
#[allow(clippy::cast_possible_truncation)] // Safe since 0 .. 16
{
scale_by = <_>::conditional_select(&scale_by, &table[i], bits.ct_eq(&(i as u8)));
}
}
res *= scale_by;
bits = 0;
}
}

11
crypto/dalek-ff-group/src/lib.rs
View File

@@ -208,7 +208,16 @@ impl Scalar {
res *= res;
}
}
res *= table[usize::from(bits)];
let mut scale_by = Scalar::ONE;
#[allow(clippy::needless_range_loop)]
for i in 0 .. 16 {
#[allow(clippy::cast_possible_truncation)] // Safe since 0 .. 16
{
scale_by = <_>::conditional_select(&scale_by, &table[i], bits.ct_eq(&(i as u8)));
}
}
res *= scale_by;
bits = 0;
}
}

11
crypto/ed448/src/backend.rs
View File

@@ -161,7 +161,16 @@ macro_rules! field {
res *= res;
}
}
res *= table[usize::from(bits)];
let mut scale_by = $FieldName(Residue::ONE);
#[allow(clippy::needless_range_loop)]
for i in 0 .. 16 {
#[allow(clippy::cast_possible_truncation)] // Safe since 0 .. 16
{
scale_by = <_>::conditional_select(&scale_by, &table[i], bits.ct_eq(&(i as u8)));
}
}
res *= scale_by;
bits = 0;
}
}

11
crypto/ed448/src/point.rs
View File

@@ -242,7 +242,16 @@ impl Mul<Scalar> for Point {
res = res.double();
}
}
res += table[usize::from(bits)];
let mut add_by = Point::identity();
#[allow(clippy::needless_range_loop)]
for i in 0 .. 16 {
#[allow(clippy::cast_possible_truncation)] // Safe since 0 .. 16
{
add_by = <_>::conditional_select(&add_by, &table[i], bits.ct_eq(&(i as u8)));
}
}
res += add_by;
bits = 0;
}
}