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use babyjubjub::{
JubjubEngine,
PrimeOrder,
edwards
};
use bellman::pairing::ff::{
PrimeField
};
use blake2_rfc::blake2s::Blake2s;
use constants;
pub fn group_hash<E: JubjubEngine>(
tag: &[u8],
personalization: &[u8],
params: &E::Params
) -> Option<edwards::Point<E, PrimeOrder>>
{
assert_eq!(personalization.len(), 8);
assert!(E::Fr::NUM_BITS == 254);
let mut h = Blake2s::with_params(32, &[], &[], personalization);
h.update(constants::GH_FIRST_BLOCK);
h.update(tag);
let h = h.finalize().as_ref().to_vec();
assert!(h.len() == 32);
match edwards::Point::<E, _>::read(&h[..], params) {
Ok(p) => {
let p = p.mul_by_cofactor(params);
if p != edwards::Point::zero() {
Some(p)
} else {
None
}
},
Err(_) => None
}
}