31 lines
1.2 KiB
Rust
31 lines
1.2 KiB
Rust
// 64 zeros, substitute with random future determined string like a blockhash, or randomness beacom
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const U: [u8; 64] = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
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// option to return None or point
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fn grouphash<E: JubjubEngine>(tag: &[u8], params: &E::Params) -> Option<montgomery::Point<E, PrimeOrder>> {
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// Check to see that scalar field is 255 bits
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assert! (E::Fr::NUM_BITS == 255);
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// Perform hash, get random 32-byte string
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let mut h = Blake2s::new_keyed(&[], 32);
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h.process(&U);
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h.process(tag);
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let h = h.fixed_result();
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// Take first unset first bit of hash
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let sign = (h[0] >> 7) == 1;
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h[0] &= 0b01111111;
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// cast to prime field representation
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let mut x0 = <E::Fr as PrimeField>::Repr::default();
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x0.read_be(&h[..]).unwrap();
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match E::Fr::from_repr(x0) {
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Ok(x0) => {
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let tmp = montgomery::Point::get_for_x(x0, sign, params).mul_by_cofactor(params);
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if tmp == mongomery::Point.zero() { None } else { Some(tmp) };
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}
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Err(_) => None
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}
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}
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