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\#242 Expand usage of black_box/zeroize

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This commit greatly expands the usage of black_box/zeroize on bits, as it
originally should have. It is likely overkill, leading to less efficient
code generation, yet does its best to be comprehensive where comprehensiveness
is extremely annoying to achieve.

In the future, this usage of black_box may be desirable to move to its own
crate.

Credit to @AaronFeickert for identifying the original commit was incomplete.
This commit is contained in:
Luke Parker
2023-03-10 06:27:44 -05:00
parent 62dfc63532
commit ad470bc969
10 changed files with 163 additions and 47 deletions
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10
crypto/dalek-ff-group/src/field.rs
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@@ -1,5 +1,6 @@
use core::ops::{Add, AddAssign, Sub, SubAssign, Neg, Mul, MulAssign};
use core::ops::{DerefMut, Add, AddAssign, Sub, SubAssign, Neg, Mul, MulAssign};
use zeroize::Zeroize;
use rand_core::RngCore;
use subtle::{
@@ -11,7 +12,7 @@ use crypto_bigint::{Integer, Encoding, U256, U512};
use group::ff::{Field, PrimeField, FieldBits, PrimeFieldBits};
use crate::{constant_time, math, from_uint};
use crate::{u8_from_bool, constant_time, math, from_uint};
// 2^255 - 19
// Uses saturating_sub because checked_sub isn't available at compile time
@@ -200,10 +201,11 @@ impl FieldElement {
let mut res = FieldElement::one();
let mut bits = 0;
for (i, bit) in other.to_le_bits().iter().rev().enumerate() {
for (i, mut bit) in other.to_le_bits().iter_mut().rev().enumerate() {
bits <<= 1;
let bit = u8::from(*bit);
let mut bit = u8_from_bool(bit.deref_mut());
bits |= bit;
bit.zeroize();
if ((i + 1) % 4) == 0 {
if i != 3 {