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use crate::{scalar_from_u64, Arity, Strength};
use ff::{Field, PrimeField, ScalarEngine};
#[derive(Clone, Debug, PartialEq)]
pub enum HashType<Fr: PrimeField, A: Arity<Fr>> {
MerkleTree,
MerkleTreeSparse(u64),
VariableLength,
ConstantLength(usize),
Encryption,
Custom(CType<Fr, A>),
}
impl<Fr: PrimeField, A: Arity<Fr>> HashType<Fr, A> {
pub fn domain_tag(&self, strength: &Strength) -> Fr {
let pow2 = |n| pow2::<Fr, A>(n);
let x_pow2 = |coeff, n| x_pow2::<Fr, A>(coeff, n);
let with_strength = |x: Fr| {
let mut tmp = x;
tmp.add_assign(&Self::strength_tag_component(strength));
tmp
};
match self {
HashType::MerkleTree => with_strength(A::tag()),
HashType::MerkleTreeSparse(bitmask) => with_strength(scalar_from_u64(*bitmask)),
HashType::VariableLength => with_strength(pow2(64)),
HashType::ConstantLength(length) => {
assert!(*length as usize <= A::to_usize());
assert!(*length as usize > 0);
with_strength(x_pow2(*length as u64, 64))
}
HashType::Encryption => with_strength(pow2(32)),
HashType::Custom(ref ctype) => ctype.domain_tag(&strength),
}
}
fn strength_tag_component(strength: &Strength) -> Fr {
let id = match strength {
Strength::Standard => 0,
Strength::Strengthened => 1,
};
x_pow2::<Fr, A>(id, 32)
}
pub fn is_supported(&self) -> bool {
match self {
HashType::MerkleTree => true,
HashType::MerkleTreeSparse(_) => false,
HashType::VariableLength => false,
HashType::ConstantLength(_) => true,
HashType::Encryption => true,
HashType::Custom(_) => false,
}
}
}
#[derive(Clone, Debug, PartialEq)]
pub enum CType<Fr: PrimeField, A: Arity<Fr>> {
Arbitrary(u64),
_Phantom((Fr, A)),
}
impl<Fr: PrimeField, A: Arity<Fr>> CType<Fr, A> {
fn identifier(&self) -> u64 {
match self {
CType::Arbitrary(id) => *id,
CType::_Phantom(_) => panic!("_Phantom is not a real custom tag type."),
}
}
fn domain_tag(&self, _strength: &Strength) -> Fr {
x_pow2::<Fr, A>(self.identifier(), 32)
}
}
fn pow2<Fr: PrimeField, A: Arity<Fr>>(n: i32) -> Fr {
let two: Fr = scalar_from_u64(2);
two.pow([n as u64, 0, 0, 0])
}
fn x_pow2<Fr: PrimeField, A: Arity<Fr>>(coeff: u64, n: i32) -> Fr {
let mut tmp: Fr = pow2::<Fr, A>(n);
tmp.mul_assign(&scalar_from_u64(coeff));
tmp
}
#[cfg(test)]
mod tests {
use super::*;
use crate::{scalar_from_u64s, Strength};
use bellperson::bls::{Bls12, Fr, FrRepr};
use generic_array::typenum::{U15, U8};
use std::collections::HashSet;
#[test]
fn test_domain_tags() {
let merkle_standard = HashType::MerkleTree::<Fr, U8>.domain_tag(&Strength::Standard);
let expected_merkle_standard = scalar_from_u64s([
0x00000000000000ff,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
assert_eq!(expected_merkle_standard, merkle_standard);
let merkle_strengthened =
HashType::MerkleTree::<Fr, U8>.domain_tag(&Strength::Strengthened);
let expected_merkle_strengthened = scalar_from_u64s([
0x00000001000000ff,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
assert_eq!(expected_merkle_strengthened, merkle_strengthened,);
let mut all_tags = Vec::new();
for length in 1..15 {
let constant_standard =
HashType::ConstantLength::<Fr, U15>(length).domain_tag(&Strength::Standard);
all_tags.push(constant_standard);
if length <= 8 {
let constant_standard_alt_arity =
HashType::ConstantLength::<Fr, U8>(length).domain_tag(&Strength::Standard);
assert_eq!(constant_standard, constant_standard_alt_arity);
}
assert_eq!(
constant_standard,
scalar_from_u64s([
0x0000000000000000,
length as u64,
0x0000000000000000,
0x0000000000000000
])
);
}
for length in 1..15 {
let constant_strengthened =
HashType::ConstantLength::<Fr, U15>(length).domain_tag(&Strength::Strengthened);
all_tags.push(constant_strengthened);
if length <= 8 {
let constant_strenghtened_alt_arity =
HashType::ConstantLength::<Fr, U8>(length).domain_tag(&Strength::Strengthened);
assert_eq!(constant_strengthened, constant_strenghtened_alt_arity);
}
assert_eq!(
constant_strengthened,
scalar_from_u64s([
0x0000000100000000,
length as u64,
0x0000000000000000,
0x0000000000000000
])
);
}
let encryption_standard = HashType::Encryption::<Fr, U8>.domain_tag(&Strength::Standard);
let expected_encryption_standard = scalar_from_u64s([
0x0000000100000000,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
assert_eq!(expected_encryption_standard, encryption_standard,);
let encryption_strengthened =
HashType::Encryption::<Fr, U8>.domain_tag(&Strength::Strengthened);
let expected_encryption_strengthened = scalar_from_u64s([
0x0000000200000000,
0x0000000000000000,
0x0000000000000000,
0x0000000000000000,
]);
assert_eq!(expected_encryption_strengthened, encryption_strengthened);
all_tags.extend(&[
expected_merkle_standard,
expected_merkle_strengthened,
expected_encryption_standard,
expected_encryption_strengthened,
]);
let mut all_tags_set = HashSet::new();
all_tags.iter().for_each(|x| {
let _ = all_tags_set.insert(x.into_repr().0);
});
assert_eq!(all_tags.len(), all_tags_set.len());
}
}