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Clear memory from avx2 multiscalar mult

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This commit is contained in:
Henry de Valence 2018-01-03 13:37:12 -08:00
parent d41dbb1fe4
commit 3686562b2f
2 changed files with 16 additions and 8 deletions
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23
src/backend/avx2/edwards.rs
View file

@ -470,11 +470,11 @@ impl EdwardsBasepointTable {
/// A vector of `Scalar`s and a vector of `ExtendedPoints`. It is an
/// error to call this function with two vectors of different lengths.
///
/// XXX need to clear memory
///
/// XXX this takes `edwards::ExtendedPoints` because we have to alloc scratch space here anyways,
/// and we need some space to store the converted points, so we may as well do the conversion here.
/// maybe there's a better way to avoid code duplication...
/// maybe there's a better way to avoid code duplication... however we can't quite just write a
/// generic `multiscalar_mult` because the non-vectorized code passes between models and this code
/// doesn't.
#[cfg(any(feature = "alloc", feature = "std"))]
pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> edwards::ExtendedPoint
where I: IntoIterator<Item = &'a Scalar>,
@ -482,17 +482,26 @@ pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> edwards::Extende
{
//assert_eq!(scalars.len(), points.len());
let lookup_tables: Vec<_> = points.into_iter()
use clear_on_drop::ClearOnDrop;
let lookup_tables_vec: Vec<_> = points.into_iter()
.map(|P| LookupTable::from(ExtendedPoint::from(*P)) )
.collect();
let lookup_tables = ClearOnDrop::new(lookup_tables_vec);
// Setting s_i = i-th scalar, compute
//
// 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_vec: Vec<_> = scalars.into_iter()
.map(|c| c.to_radix_16())
.collect();
// The above puts the scalar digits into a heap-allocated Vec.
// To ensure that these are erased, pass ownership of the Vec into a
// ClearOnDrop wrapper.
let scalar_digits = ClearOnDrop::new(scalar_digits_vec);
// Compute s_1*P_1 + ... + s_n*P_n: since
//
@ -517,7 +526,7 @@ pub fn multiscalar_mult<'a, 'b, I, J>(scalars: I, points: J) -> edwards::Extende
// XXX this algorithm makes no effort to be cache-aware; maybe it could be improved?
for j in (0..64).rev() {
Q = Q.mult_by_pow_2(4);
let it = scalar_digits_list.iter().zip(lookup_tables.iter());
let it = scalar_digits.iter().zip(lookup_tables.iter());
for (s_i, lookup_table_i) in it {
// Q = Q + s_{i,j} * P_i
Q = &Q + &lookup_table_i.select(s_i[j]);

1
src/edwards.rs
View file

@ -496,7 +496,6 @@ impl<'a, 'b> Mul<&'b ExtendedPoint> for &'a Scalar {
/// A iterable of `Scalar`s and a iterable of `ExtendedPoints`. It is an
/// error to call this function with two iterators of different lengths.
///
/// XXX need to clear memory
// XXX later when we do more fancy multiscalar mults, we can delegate
// based on the iter's size hint -- hdevalence
#[cfg(any(feature = "alloc", feature = "std"))]