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https://github.com/Qortal/pirate-librustzcash.git
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Remove Montgomery point doubling implementation in the circuit.
This commit is contained in:
Sean Bowe
parent
1610bcfbcf
commit
c89d47bb07
@ -650,109 +650,6 @@ impl<E: JubjubEngine> MontgomeryPoint<E> {
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y: yprime
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})
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}
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/// Performs an affine point doubling, not defined for
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/// the point of order two (0, 0).
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pub fn double<CS>(
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&self,
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mut cs: CS,
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params: &E::Params
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) -> Result<Self, SynthesisError>
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where CS: ConstraintSystem<E>
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{
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// Square x
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let xx = self.x.square(&mut cs)?;
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// Compute lambda = (3.xx + 2.A.x + 1) / 2.y
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let lambda = AllocatedNum::alloc(cs.namespace(|| "lambda"), || {
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let mut t0 = *xx.get_value().get()?;
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let mut t1 = t0;
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t0.double(); // t0 = 2.xx
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t0.add_assign(&t1); // t0 = 3.xx
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t1 = *self.x.get_value().get()?; // t1 = x
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t1.mul_assign(params.montgomery_2a()); // t1 = 2.A.x
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t0.add_assign(&t1);
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t0.add_assign(&E::Fr::one());
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t1 = *self.y.get_value().get()?; // t1 = y
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t1.double(); // t1 = 2.y
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match t1.inverse() {
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Some(t1) => {
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t0.mul_assign(&t1);
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Ok(t0)
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},
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None => {
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Err(SynthesisError::DivisionByZero)
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}
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}
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})?;
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// (2.y) * (lambda) = (3.xx + 2.A.x + 1)
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let one = CS::one();
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cs.enforce(
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|| "evaluate lambda",
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|lc| lc + self.y.get_variable()
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+ self.y.get_variable(),
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|lc| lc + lambda.get_variable(),
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|lc| lc + xx.get_variable()
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+ xx.get_variable()
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+ xx.get_variable()
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+ (*params.montgomery_2a(), self.x.get_variable())
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+ one
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);
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// Compute x' = (lambda^2) - A - 2.x
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let xprime = AllocatedNum::alloc(cs.namespace(|| "xprime"), || {
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let mut t0 = *lambda.get_value().get()?;
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t0.square();
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t0.sub_assign(params.montgomery_a());
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t0.sub_assign(self.x.get_value().get()?);
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t0.sub_assign(self.x.get_value().get()?);
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Ok(t0)
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})?;
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// (lambda) * (lambda) = (A + 2.x + x')
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cs.enforce(
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|| "evaluate xprime",
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|lc| lc + lambda.get_variable(),
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|lc| lc + lambda.get_variable(),
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|lc| lc + (*params.montgomery_a(), one)
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+ self.x.get_variable()
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+ self.x.get_variable()
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+ xprime.get_variable()
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);
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// Compute y' = -(y + lambda(x' - x))
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let yprime = AllocatedNum::alloc(cs.namespace(|| "yprime"), || {
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let mut t0 = *xprime.get_value().get()?;
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t0.sub_assign(self.x.get_value().get()?);
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t0.mul_assign(lambda.get_value().get()?);
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t0.add_assign(self.y.get_value().get()?);
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t0.negate();
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Ok(t0)
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})?;
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// y' + y = lambda(x - x')
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cs.enforce(
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|| "evaluate yprime",
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|lc| lc + self.x.get_variable()
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- xprime.get_variable(),
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|lc| lc + lambda.get_variable(),
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|lc| lc + yprime.get_variable()
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+ self.y.get_variable()
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);
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Ok(MontgomeryPoint {
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x: xprime,
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y: yprime
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})
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}
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}
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#[cfg(test)]
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@ -863,27 +760,6 @@ mod test {
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}
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}
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#[test]
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fn test_doubling_order_2() {
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let params = &JubjubBls12::new();
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let mut cs = TestConstraintSystem::<Bls12>::new();
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let x = AllocatedNum::alloc(cs.namespace(|| "x"), || {
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Ok(Fr::zero())
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}).unwrap();
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let y = AllocatedNum::alloc(cs.namespace(|| "y"), || {
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Ok(Fr::zero())
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}).unwrap();
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let p = MontgomeryPoint {
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x: x,
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y: y
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};
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assert!(p.double(&mut cs, params).is_err());
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}
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#[test]
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fn test_edwards_fixed_base_multiplication() {
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let params = &JubjubBls12::new();
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@ -1222,60 +1098,4 @@ mod test {
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assert_eq!(cs.which_is_unsatisfied(), Some("addition/evaluate lambda"));
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}
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}
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#[test]
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fn test_montgomery_doubling() {
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let params = &JubjubBls12::new();
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let rng = &mut XorShiftRng::from_seed([0x5dbe6259, 0x8d313d76, 0x3237db17, 0xe5bc0654]);
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for _ in 0..100 {
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let p = loop {
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let x: Fr = rng.gen();
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let s: bool = rng.gen();
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if let Some(p) = montgomery::Point::<Bls12, _>::get_for_x(x, s, params) {
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break p;
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}
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};
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let p2 = p.double(params);
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let (x0, y0) = p.into_xy().unwrap();
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let (x1, y1) = p2.into_xy().unwrap();
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let mut cs = TestConstraintSystem::<Bls12>::new();
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let x = AllocatedNum::alloc(cs.namespace(|| "x"), || {
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Ok(x0)
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}).unwrap();
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let y = AllocatedNum::alloc(cs.namespace(|| "y"), || {
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Ok(y0)
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}).unwrap();
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let p = MontgomeryPoint {
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x: x,
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y: y
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};
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let p2 = p.double(cs.namespace(|| "doubling"), params).unwrap();
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assert!(cs.is_satisfied());
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assert!(p2.x.get_value().unwrap() == x1);
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assert!(p2.y.get_value().unwrap() == y1);
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cs.set("doubling/yprime/num", rng.gen());
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assert_eq!(cs.which_is_unsatisfied(), Some("doubling/evaluate yprime"));
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cs.set("doubling/yprime/num", y1);
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assert!(cs.is_satisfied());
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cs.set("doubling/xprime/num", rng.gen());
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assert_eq!(cs.which_is_unsatisfied(), Some("doubling/evaluate xprime"));
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cs.set("doubling/xprime/num", x1);
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assert!(cs.is_satisfied());
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cs.set("doubling/lambda/num", rng.gen());
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assert_eq!(cs.which_is_unsatisfied(), Some("doubling/evaluate lambda"));
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}
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}
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}
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