111 lines
2.8 KiB
Rust
111 lines
2.8 KiB
Rust
use std::marker::PhantomData;
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use super::{Engine, Curve, PrimeField, PrimeFieldRepr};
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/// Represents the scratch space for a wNAF form scalar.
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pub struct WNAFTable {
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window: usize,
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wnaf: Vec<i64>
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}
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impl WNAFTable {
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pub fn new() -> WNAFTable {
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WNAFTable {
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window: 0,
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wnaf: vec![]
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}
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}
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/// Convert the scalar into wNAF form.
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pub fn set_scalar<E: Engine, G: Curve<E>>(&mut self, table: &WindowTable<E, G>, mut c: <E::Fr as PrimeField<E>>::Repr) {
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self.window = table.window;
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self.wnaf.truncate(0);
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while !c.is_zero() {
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let mut u;
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if c.is_odd() {
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u = (c.as_ref()[0] % (1 << (self.window+1))) as i64;
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if u > (1 << self.window) {
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u -= 1 << (self.window+1);
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}
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if u > 0 {
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c.sub_noborrow(&<<E::Fr as PrimeField<E>>::Repr as PrimeFieldRepr>::from_u64(u as u64));
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} else {
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c.add_nocarry(&<<E::Fr as PrimeField<E>>::Repr as PrimeFieldRepr>::from_u64((-u) as u64));
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}
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} else {
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u = 0;
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}
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self.wnaf.push(u);
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c.div2();
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}
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}
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}
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/// Represents a window table for a base curve point.
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pub struct WindowTable<E: Engine, G: Curve<E>>{
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window: usize,
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table: Vec<G>,
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_marker: PhantomData<E>
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}
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impl<E: Engine, G: Curve<E>> WindowTable<E, G> {
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/// Construct a new window table for a given base.
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pub fn new(e: &E, base: G, window: usize) -> Self {
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let mut tmp = WindowTable {
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window: 0,
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table: vec![],
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_marker: PhantomData
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};
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tmp.set_base(e, base, window);
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tmp
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}
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/// Replace this window table with a new one generated by a different base.
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pub fn set_base(&mut self, e: &E, mut base: G, window: usize) {
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assert!(window < 23);
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assert!(window > 1);
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self.window = window;
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self.table.truncate(0);
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self.table.reserve(1 << (window-1));
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let mut dbl = base;
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dbl.double(e);
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for _ in 0..(1 << (window-1)) {
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self.table.push(base);
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base.add_assign(e, &dbl);
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}
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}
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pub fn exp(&self, e: &E, wnaf: &WNAFTable) -> G {
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assert_eq!(wnaf.window, self.window);
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let mut result = G::zero(e);
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for n in wnaf.wnaf.iter().rev() {
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result.double(e);
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if *n != 0 {
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if *n > 0 {
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result.add_assign(e, &self.table[(n/2) as usize]);
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} else {
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result.sub_assign(e, &self.table[((-n)/2) as usize]);
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}
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}
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}
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result
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}
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pub fn current_window(&self) -> usize {
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self.window
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}
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}
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