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Doing math in u16 collector obviates passing of Bit(Slice/Vector) 

But I added a max 10-bit value check in S() on j.
This commit is contained in:
Deirdre Connolly 2021-04-27 18:53:28 -04:00
parent af32851aa1
commit 26fc6b1908
1 changed files with 12 additions and 5 deletions
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17
zebra-chain/src/orchard/sinsemilla.rs
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@ -47,10 +47,13 @@ fn Q(D: &[u8]) -> pallas::Point {
/// S: {0 .. 2^k - 1} -> P^*, aka 10 bits hashed into the group /// S: {0 .. 2^k - 1} -> P^*, aka 10 bits hashed into the group
/// ///
/// https://zips.z.cash/protocol/protocol.pdf#concretesinsemillahash /// https://zips.z.cash/protocol/protocol.pdf#concretesinsemillahash
// XXX: should j be strictly limited to k=10 bits?
#[allow(non_snake_case)] #[allow(non_snake_case)]
fn S(j: [u8; 2]) -> pallas::Point { fn S(j: &u16) -> pallas::Point {
pallas_group_hash(b"z.cash:SinsemillaS", &j) // The value of j is a 10-bit value, therefore must never exceed 2^10 in
// value.
assert!(j < &1024u16);
pallas_group_hash(b"z.cash:SinsemillaS", &j.to_le_bytes())
} }
/// "...an algebraic hash function with collision resistance (for fixed input /// "...an algebraic hash function with collision resistance (for fixed input
@ -89,9 +92,13 @@ pub fn sinsemilla_hash_to_point(D: &[u8], M: &BitVec<Lsb0, u8>) -> pallas::Point
.for_each(|(i, bit)| bits.set(i, *bit)); .for_each(|(i, bit)| bits.set(i, *bit));
// An instance of LEBS2IP_k // An instance of LEBS2IP_k
let j = &bits.iter().fold(0u16, |j, &bit| j * 2 + bit as u16); // XXX: does Rust or bitvec have a better implementation?
let j = &bits
.iter()
.enumerate()
.fold(0u16, |j, (i, &bit)| j + if bit { 1 << i } else { 0 });
acc = acc + acc + S(j.to_le_bytes()); acc = acc + acc + S(j);
} }
acc acc