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Merge pull request #276 from dalek-cryptography/quarkslab

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Fix issues found in Quarkslab audit
This commit is contained in:
Henry de Valence 2019-08-06 16:08:23 -07:00 committed by GitHub
commit 4bc2ec0082
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GPG key ID: 4AEE18F83AFDEB23
2 changed files with 132 additions and 7 deletions
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137
src/scalar.rs
View file

@ -297,7 +297,7 @@ define_mul_variants!(LHS = Scalar, RHS = Scalar, Output = Scalar);
impl<'b> AddAssign<&'b Scalar> for Scalar {
fn add_assign(&mut self, _rhs: &'b Scalar) {
*self = UnpackedScalar::add(&self.unpack(), &_rhs.unpack()).pack();
*self = *self + _rhs;
}
}
@ -305,8 +305,17 @@ define_add_assign_variants!(LHS = Scalar, RHS = Scalar);
impl<'a, 'b> Add<&'b Scalar> for &'a Scalar {
type Output = Scalar;
#[allow(non_snake_case)]
fn add(self, _rhs: &'b Scalar) -> Scalar {
UnpackedScalar::add(&self.unpack(), &_rhs.unpack()).pack()
// The UnpackedScalar::add function produces reduced outputs
// if the inputs are reduced. However, these inputs may not
// be reduced -- they might come from Scalar::from_bits. So
// after computing the sum, we explicitly reduce it mod l
// before repacking.
let sum = UnpackedScalar::add(&self.unpack(), &_rhs.unpack());
let sum_R = UnpackedScalar::mul_internal(&sum, &constants::R);
let sum_mod_l = UnpackedScalar::montgomery_reduce(&sum_R);
sum_mod_l.pack()
}
}
@ -314,7 +323,7 @@ define_add_variants!(LHS = Scalar, RHS = Scalar, Output = Scalar);
impl<'b> SubAssign<&'b Scalar> for Scalar {
fn sub_assign(&mut self, _rhs: &'b Scalar) {
*self = UnpackedScalar::sub(&self.unpack(), &_rhs.unpack()).pack();
*self = *self - _rhs;
}
}
@ -322,8 +331,18 @@ define_sub_assign_variants!(LHS = Scalar, RHS = Scalar);
impl<'a, 'b> Sub<&'b Scalar> for &'a Scalar {
type Output = Scalar;
fn sub(self, _rhs: &'b Scalar) -> Scalar {
UnpackedScalar::sub(&self.unpack(), &_rhs.unpack()).pack()
#[allow(non_snake_case)]
fn sub(self, rhs: &'b Scalar) -> Scalar {
// The UnpackedScalar::sub function requires reduced inputs
// and produces reduced output. However, these inputs may not
// be reduced -- they might come from Scalar::from_bits. So
// we explicitly reduce the inputs.
let self_R = UnpackedScalar::mul_internal(&self.unpack(), &constants::R);
let self_mod_l = UnpackedScalar::montgomery_reduce(&self_R);
let rhs_R = UnpackedScalar::mul_internal(&rhs.unpack(), &constants::R);
let rhs_mod_l = UnpackedScalar::montgomery_reduce(&rhs_R);
UnpackedScalar::sub(&self_mod_l, &rhs_mod_l).pack()
}
}
@ -331,8 +350,11 @@ define_sub_variants!(LHS = Scalar, RHS = Scalar, Output = Scalar);
impl<'a> Neg for &'a Scalar {
type Output = Scalar;
#[allow(non_snake_case)]
fn neg(self) -> Scalar {
&Scalar::zero() - self
let self_R = UnpackedScalar::mul_internal(&self.unpack(), &constants::R);
let self_mod_l = UnpackedScalar::montgomery_reduce(&self_R);
UnpackedScalar::sub(&UnpackedScalar::zero(), &self_mod_l).pack()
}
}
@ -1233,6 +1255,33 @@ mod test {
0,0,0,11,0,0,0,0,0,15,0,0,0,0,0,-9,0,0,0,0,0,0,0,-1,0,0,0,0,0,0,0,7,
0,0,0,0,0,-15,0,0,0,0,0,15,0,0,0,0,15,0,0,0,0,15,0,0,0,0,0,1,0,0,0,0];
static LARGEST_ED25519_S: Scalar = Scalar {
bytes: [
0xf8, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f,
],
};
static CANONICAL_LARGEST_ED25519_S_PLUS_ONE: Scalar = Scalar {
bytes: [
0x7e, 0x34, 0x47, 0x75, 0x47, 0x4a, 0x7f, 0x97,
0x23, 0xb6, 0x3a, 0x8b, 0xe9, 0x2a, 0xe7, 0x6d,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x0f,
],
};
static CANONICAL_LARGEST_ED25519_S_MINUS_ONE: Scalar = Scalar {
bytes: [
0x7c, 0x34, 0x47, 0x75, 0x47, 0x4a, 0x7f, 0x97,
0x23, 0xb6, 0x3a, 0x8b, 0xe9, 0x2a, 0xe7, 0x6d,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x0f,
],
};
#[test]
fn fuzzer_testcase_reduction() {
// LE bytes of 24519928653854221733733552434404946937899825954937634815
@ -1322,6 +1371,82 @@ mod test {
}
}
#[test]
fn add_reduces() {
// Check that the addition works
assert_eq!(
(LARGEST_ED25519_S + Scalar::one()).reduce(),
CANONICAL_LARGEST_ED25519_S_PLUS_ONE
);
// Check that the addition reduces
assert_eq!(
LARGEST_ED25519_S + Scalar::one(),
CANONICAL_LARGEST_ED25519_S_PLUS_ONE
);
}
#[test]
fn sub_reduces() {
// Check that the subtraction works
assert_eq!(
(LARGEST_ED25519_S - Scalar::one()).reduce(),
CANONICAL_LARGEST_ED25519_S_MINUS_ONE
);
// Check that the subtraction reduces
assert_eq!(
LARGEST_ED25519_S - Scalar::one(),
CANONICAL_LARGEST_ED25519_S_MINUS_ONE
);
}
#[test]
fn quarkslab_scalar_overflow_does_not_occur() {
// Check that manually-constructing large Scalars with
// from_bits cannot produce incorrect results.
//
// The from_bits function is required to implement X/Ed25519,
// while all other methods of constructing a Scalar produce
// reduced Scalars. However, this "invariant loophole" allows
// constructing large scalars which are not reduced mod l.
//
// This issue was discovered independently by both Jack
// "str4d" Grigg (issue #238), who noted that reduction was
// not performed on addition, and Laurent Grémy & Nicolas
// Surbayrole of Quarkslab, who noted that it was possible to
// cause an overflow and compute incorrect results.
//
// This test is adapted from the one suggested by Quarkslab.
let large_bytes = [
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x7f,
];
let a = Scalar::from_bytes_mod_order(large_bytes);
let b = Scalar::from_bits(large_bytes);
assert_eq!(a, b.reduce());
let a_3 = a + a + a;
let b_3 = b + b + b;
assert_eq!(a_3, b_3);
let neg_a = -a;
let neg_b = -b;
assert_eq!(neg_a, neg_b);
let minus_a_3 = Scalar::zero() - a - a - a;
let minus_b_3 = Scalar::zero() - b - b - b;
assert_eq!(minus_a_3, minus_b_3);
assert_eq!(minus_a_3, -a_3);
assert_eq!(minus_b_3, -b_3);
}
#[test]
fn impl_add() {
let two = Scalar::from(2u64);

2
src/window.rs
View file

@ -171,7 +171,7 @@ pub(crate) struct NafLookupTable8<T>(pub(crate) [T; 64]);
impl<T: Copy> NafLookupTable8<T> {
pub fn select(&self, x: usize) -> T {
debug_assert_eq!(x & 1, 1);
debug_assert!(x < 256);
debug_assert!(x < 128);
self.0[x / 2]
}