104 lines
2.6 KiB
Rust
104 lines
2.6 KiB
Rust
use jubjub::*;
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use pairing::*;
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#[derive(Copy, Clone)]
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pub enum Personalization {
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NoteCommitment,
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MerkleTree(usize)
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}
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impl Personalization {
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pub fn get_bits(&self) -> Vec<bool> {
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match *self {
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Personalization::NoteCommitment =>
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vec![true, true, true, true, true, true],
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Personalization::MerkleTree(num) => {
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assert!(num < 63);
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(0..6).map(|i| (num >> i) & 1 == 1).collect()
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}
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}
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}
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}
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pub fn pedersen_hash<E, I>(
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personalization: Personalization,
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bits: I,
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params: &E::Params
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) -> edwards::Point<E, PrimeOrder>
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where I: IntoIterator<Item=bool>,
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E: JubjubEngine
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{
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let mut bits = personalization.get_bits().into_iter().chain(bits.into_iter());
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let mut result = edwards::Point::zero();
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let mut generators = params.pedersen_hash_exp_table().iter();
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loop {
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let mut acc = E::Fs::zero();
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let mut cur = E::Fs::one();
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let mut chunks_remaining = params.pedersen_hash_chunks_per_generator();
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let mut encountered_bits = false;
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// Grab three bits from the input
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while let Some(a) = bits.next() {
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encountered_bits = true;
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let b = bits.next().unwrap_or(false);
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let c = bits.next().unwrap_or(false);
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// Start computing this portion of the scalar
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let mut tmp = cur;
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if a {
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tmp.add_assign(&cur);
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}
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cur.double(); // 2^1 * cur
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if b {
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tmp.add_assign(&cur);
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}
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// conditionally negate
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if c {
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tmp.negate();
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}
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acc.add_assign(&tmp);
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chunks_remaining -= 1;
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if chunks_remaining == 0 {
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break;
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} else {
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cur.double(); // 2^2 * cur
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cur.double(); // 2^3 * cur
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cur.double(); // 2^4 * cur
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}
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}
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if !encountered_bits {
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break;
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}
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let mut table: &[Vec<edwards::Point<E, _>>] = &generators.next().expect("we don't have enough generators");
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let window = JubjubBls12::pedersen_hash_exp_window_size();
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let window_mask = (1 << window) - 1;
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let mut acc = acc.into_repr();
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let mut tmp = edwards::Point::zero();
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while !acc.is_zero() {
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let i = (acc.as_ref()[0] & window_mask) as usize;
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tmp = tmp.add(&table[0][i], params);
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acc.shr(window);
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table = &table[1..];
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}
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result = result.add(&tmp, params);
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}
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result
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}
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