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package how.monero.hodl.bulletproof;
import how.monero.hodl.crypto.Curve25519Point;
import how.monero.hodl.crypto.Scalar;
import how.monero.hodl.crypto.CryptoUtil;
import how.monero.hodl.util.ByteUtil;
import java.math.BigInteger;
import how.monero.hodl.util.VarInt;
import java.util.Random;
import static how.monero.hodl.crypto.Scalar.randomScalar;
import static how.monero.hodl.crypto.CryptoUtil.*;
import static how.monero.hodl.util.ByteUtil.*;
public class LinearBulletproof
{
private static int N;
private static Curve25519Point G;
private static Curve25519Point H;
private static Curve25519Point[] Gi;
private static Curve25519Point[] Hi;
public static class ProofTuple
{
private Curve25519Point V;
private Curve25519Point A;
private Curve25519Point S;
private Curve25519Point T1;
private Curve25519Point T2;
private Scalar taux;
private Scalar mu;
private Scalar[] l;
private Scalar[] r;
public ProofTuple(Curve25519Point V, Curve25519Point A, Curve25519Point S, Curve25519Point T1, Curve25519Point T2, Scalar taux, Scalar mu, Scalar[] l, Scalar[] r)
{
this.V = V;
this.A = A;
this.S = S;
this.T1 = T1;
this.T2 = T2;
this.taux = taux;
this.mu = mu;
this.l = l;
this.r = r;
}
}
/* Given two scalar arrays, construct a vector commitment */
public static Curve25519Point VectorExponent(Scalar[] a, Scalar[] b)
{
Curve25519Point Result = Curve25519Point.ZERO;
for (int i = 0; i < N; i++)
{
Result = Result.add(Gi[i].scalarMultiply(a[i]));
Result = Result.add(Hi[i].scalarMultiply(b[i]));
}
return Result;
}
/* Given a scalar, construct a vector of powers */
public static Scalar[] VectorPowers(Scalar x)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = x.pow(i);
}
return result;
}
/* Given two scalar arrays, construct the inner product */
public static Scalar InnerProduct(Scalar[] a, Scalar[] b)
{
Scalar result = Scalar.ZERO;
for (int i = 0; i < N; i++)
{
result = result.add(a[i].mul(b[i]));
}
return result;
}
/* Given two scalar arrays, construct the Hadamard product */
public static Scalar[] Hadamard(Scalar[] a, Scalar[] b)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = a[i].mul(b[i]);
}
return result;
}
/* Add two vectors */
public static Scalar[] VectorAdd(Scalar[] a, Scalar[] b)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = a[i].add(b[i]);
}
return result;
}
/* Subtract two vectors */
public static Scalar[] VectorSubtract(Scalar[] a, Scalar[] b)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = a[i].sub(b[i]);
}
return result;
}
/* Multiply a scalar and a vector */
public static Scalar[] VectorScalar(Scalar[] a, Scalar x)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = a[i].mul(x);
}
return result;
}
/* Compute the inverse of a scalar, the stupid way */
public static Scalar Invert(Scalar x)
{
Scalar inverse = new Scalar(x.toBigInteger().modInverse(CryptoUtil.l));
assert x.mul(inverse).equals(Scalar.ONE);
return inverse;
}
/* Given a value v (0..2^N-1) and a mask gamma, construct a range proof */
public static ProofTuple PROVE(Scalar v, Scalar gamma)
{
Curve25519Point V = G.scalarMultiply(v).add(H.scalarMultiply(gamma));
// PAPER LINES 36-37
Scalar[] aL = new Scalar[N];
Scalar[] aR = new Scalar[N];
BigInteger tempV = v.toBigInteger();
for (int i = N-1; i >= 0; i--)
{
BigInteger basePow = BigInteger.valueOf(2).pow(i);
if (tempV.divide(basePow).equals(BigInteger.ZERO))
{
aL[i] = Scalar.ZERO;
}
else
{
aL[i] = Scalar.ONE;
tempV = tempV.subtract(basePow);
}
aR[i] = aL[i].sub(Scalar.ONE);
}
// DEBUG: Test to ensure this recovers the value
BigInteger test_aL = BigInteger.ZERO;
BigInteger test_aR = BigInteger.ZERO;
for (int i = 0; i < N; i++)
{
if (aL[i].equals(Scalar.ONE))
test_aL = test_aL.add(BigInteger.valueOf(2).pow(i));
if (aR[i].equals(Scalar.ZERO))
test_aR = test_aR.add(BigInteger.valueOf(2).pow(i));
}
assert test_aL.equals(v.toBigInteger());
assert test_aR.equals(v.toBigInteger());
// PAPER LINES 38-39
Scalar alpha = randomScalar();
Curve25519Point A = VectorExponent(aL,aR).add(H.scalarMultiply(alpha));
// PAPER LINES 40-42
Scalar[] sL = new Scalar[N];
Scalar[] sR = new Scalar[N];
for (int i = 0; i < N; i++)
{
sL[i] = randomScalar();
sR[i] = randomScalar();
}
Scalar rho = randomScalar();
Curve25519Point S = VectorExponent(sL,sR).add(H.scalarMultiply(rho));
// PAPER LINES 43-45
Scalar y = hashToScalar(concat(A.toBytes(),S.toBytes()));
Scalar z = hashToScalar(y.bytes);
Scalar t0 = Scalar.ZERO;
Scalar t1 = Scalar.ZERO;
Scalar t2 = Scalar.ZERO;
t0 = t0.add(z.mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
t0 = t0.add(z.sq().mul(v));
Scalar k = Scalar.ZERO;
k = k.sub(z.sq().mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
k = k.sub(z.pow(3).mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(Scalar.TWO))));
t0 = t0.add(k);
// DEBUG: Test the value of t0 has the correct form
Scalar test_t0 = Scalar.ZERO;
test_t0 = test_t0.add(InnerProduct(aL,Hadamard(aR,VectorPowers(y))));
test_t0 = test_t0.add(z.mul(InnerProduct(VectorSubtract(aL,aR),VectorPowers(y))));
test_t0 = test_t0.add(z.sq().mul(InnerProduct(VectorPowers(Scalar.TWO),aL)));
test_t0 = test_t0.add(k);
assert test_t0.equals(t0);
t1 = t1.add(InnerProduct(VectorSubtract(aL,VectorScalar(VectorPowers(Scalar.ONE),z)),Hadamard(VectorPowers(y),sR)));
t1 = t1.add(InnerProduct(sL,VectorAdd(Hadamard(VectorPowers(y),VectorAdd(aR,VectorScalar(VectorPowers(Scalar.ONE),z))),VectorScalar(VectorPowers(Scalar.TWO),z.sq()))));
t2 = t2.add(InnerProduct(sL,Hadamard(VectorPowers(y),sR)));
// PAPER LINES 47-48
Scalar tau1 = randomScalar();
Scalar tau2 = randomScalar();
Curve25519Point T1 = G.scalarMultiply(t1).add(H.scalarMultiply(tau1));
Curve25519Point T2 = G.scalarMultiply(t2).add(H.scalarMultiply(tau2));
// PAPER LINES 49-51
Scalar x = hashToScalar(concat(z.bytes,T1.toBytes(),T2.toBytes()));
// PAPER LINES 52-53
Scalar taux = Scalar.ZERO;
taux = tau1.mul(x);
taux = taux.add(tau2.mul(x.sq()));
taux = taux.add(gamma.mul(z.sq()));
Scalar mu = x.mul(rho).add(alpha);
// PAPER LINES 54-57
Scalar[] l = new Scalar[N];
Scalar[] r = new Scalar[N];
l = VectorAdd(VectorSubtract(aL,VectorScalar(VectorPowers(Scalar.ONE),z)),VectorScalar(sL,x));
r = VectorAdd(Hadamard(VectorPowers(y),VectorAdd(aR,VectorAdd(VectorScalar(VectorPowers(Scalar.ONE),z),VectorScalar(sR,x)))),VectorScalar(VectorPowers(Scalar.TWO),z.sq()));
// DEBUG: Test if the l and r vectors match the polynomial forms
Scalar test_t = Scalar.ZERO;
test_t = test_t.add(t0).add(t1.mul(x));
test_t = test_t.add(t2.mul(x.sq()));
assert test_t.equals(InnerProduct(l,r));
// PAPER LINE 58
return new ProofTuple(V,A,S,T1,T2,taux,mu,l,r);
}
/* Given a range proof, determine if it is valid */
public static boolean VERIFY(ProofTuple proof)
{
// Reconstruct the challenges
Scalar y = hashToScalar(concat(proof.A.toBytes(),proof.S.toBytes()));
Scalar z = hashToScalar(y.bytes);
Scalar x = hashToScalar(concat(z.bytes,proof.T1.toBytes(),proof.T2.toBytes()));
// PAPER LINE 60
Scalar t = InnerProduct(proof.l,proof.r);
// PAPER LINE 61
Curve25519Point L61Left = H.scalarMultiply(proof.taux).add(G.scalarMultiply(t));
Scalar k = Scalar.ZERO;
k = k.sub(z.sq().mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
k = k.sub(z.pow(3).mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(Scalar.TWO))));
Curve25519Point L61Right = G.scalarMultiply(k.add(z.mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y)))));
L61Right = L61Right.add(proof.V.scalarMultiply(z.sq()));
L61Right = L61Right.add(proof.T1.scalarMultiply(x));
L61Right = L61Right.add(proof.T2.scalarMultiply(x.sq()));
if (!L61Right.equals(L61Left))
{
return false;
}
// PAPER LINE 62
Curve25519Point P = Curve25519Point.ZERO;
P = P.add(proof.A);
P = P.add(proof.S.scalarMultiply(x));
Scalar[] Gexp = new Scalar[N];
for (int i = 0; i < N; i++)
Gexp[i] = Scalar.ZERO.sub(z);
Scalar[] Hexp = new Scalar[N];
for (int i = 0; i < N; i++)
{
Hexp[i] = Scalar.ZERO;
Hexp[i] = Hexp[i].add(z.mul(y.pow(i)));
Hexp[i] = Hexp[i].add(z.sq().mul(Scalar.TWO.pow(i)));
Hexp[i] = Hexp[i].mul(Invert(y).pow(i));
}
P = P.add(VectorExponent(Gexp,Hexp));
// PAPER LINE 63
for (int i = 0; i < N; i++)
{
Hexp[i] = Scalar.ZERO;
Hexp[i] = Hexp[i].add(proof.r[i]);
Hexp[i] = Hexp[i].mul(Invert(y).pow(i));
}
Curve25519Point L63Right = VectorExponent(proof.l,Hexp).add(H.scalarMultiply(proof.mu));
if (!L63Right.equals(P))
{
return false;
}
return true;
}
public static void main(String[] args)
{
// Number of bits in the range
N = 64;
// Set the curve base points
G = Curve25519Point.G;
H = Curve25519Point.hashToPoint(G);
Gi = new Curve25519Point[N];
Hi = new Curve25519Point[N];
for (int i = 0; i < N; i++)
{
Gi[i] = getHpnGLookup(i);
Hi[i] = getHpnGLookup(N+i);
}
// Run a bunch of randomized trials
Random rando = new Random();
int TRIALS = 250;
int count = 0;
while (count < TRIALS)
{
long amount = rando.nextLong();
if (amount > Math.pow(2,N)-1 || amount < 0)
continue;
ProofTuple proof = PROVE(new Scalar(BigInteger.valueOf(amount)),randomScalar());
if (!VERIFY(proof))
System.out.println("Test failed");
count += 1;
}
}
}

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package how.monero.hodl.bulletproof;
import how.monero.hodl.crypto.Curve25519Point;
import how.monero.hodl.crypto.Scalar;
import how.monero.hodl.crypto.CryptoUtil;
import java.math.BigInteger;
import java.util.Random;
import static how.monero.hodl.crypto.Scalar.randomScalar;
import static how.monero.hodl.crypto.CryptoUtil.*;
import static how.monero.hodl.util.ByteUtil.*;
public class LogBulletproof
{
private static int N;
private static int logN;
private static Curve25519Point G;
private static Curve25519Point H;
private static Curve25519Point[] Gi;
private static Curve25519Point[] Hi;
public static class ProofTuple
{
private Curve25519Point V;
private Curve25519Point A;
private Curve25519Point S;
private Curve25519Point T1;
private Curve25519Point T2;
private Scalar taux;
private Scalar mu;
private Curve25519Point[] L;
private Curve25519Point[] R;
private Scalar a;
private Scalar b;
private Scalar t;
public ProofTuple(Curve25519Point V, Curve25519Point A, Curve25519Point S, Curve25519Point T1, Curve25519Point T2, Scalar taux, Scalar mu, Curve25519Point[] L, Curve25519Point[] R, Scalar a, Scalar b, Scalar t)
{
this.V = V;
this.A = A;
this.S = S;
this.T1 = T1;
this.T2 = T2;
this.taux = taux;
this.mu = mu;
this.L = L;
this.R = R;
this.a = a;
this.b = b;
this.t = t;
}
}
/* Given two scalar arrays, construct a vector commitment */
public static Curve25519Point VectorExponent(Scalar[] a, Scalar[] b)
{
assert a.length == N && b.length == N;
Curve25519Point Result = Curve25519Point.ZERO;
for (int i = 0; i < N; i++)
{
Result = Result.add(Gi[i].scalarMultiply(a[i]));
Result = Result.add(Hi[i].scalarMultiply(b[i]));
}
return Result;
}
/* Compute a custom vector-scalar commitment */
public static Curve25519Point VectorExponentCustom(Curve25519Point[] A, Curve25519Point[] B, Scalar[] a, Scalar[] b)
{
assert a.length == A.length && b.length == B.length && a.length == b.length;
Curve25519Point Result = Curve25519Point.ZERO;
for (int i = 0; i < a.length; i++)
{
Result = Result.add(A[i].scalarMultiply(a[i]));
Result = Result.add(B[i].scalarMultiply(b[i]));
}
return Result;
}
/* Given a scalar, construct a vector of powers */
public static Scalar[] VectorPowers(Scalar x)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = x.pow(i);
}
return result;
}
/* Given two scalar arrays, construct the inner product */
public static Scalar InnerProduct(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar result = Scalar.ZERO;
for (int i = 0; i < a.length; i++)
{
result = result.add(a[i].mul(b[i]));
}
return result;
}
/* Given two scalar arrays, construct the Hadamard product */
public static Scalar[] Hadamard(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].mul(b[i]);
}
return result;
}
/* Given two curvepoint arrays, construct the Hadamard product */
public static Curve25519Point[] Hadamard2(Curve25519Point[] A, Curve25519Point[] B)
{
assert A.length == B.length;
Curve25519Point[] Result = new Curve25519Point[A.length];
for (int i = 0; i < A.length; i++)
{
Result[i] = A[i].add(B[i]);
}
return Result;
}
/* Add two vectors */
public static Scalar[] VectorAdd(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].add(b[i]);
}
return result;
}
/* Subtract two vectors */
public static Scalar[] VectorSubtract(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].sub(b[i]);
}
return result;
}
/* Multiply a scalar and a vector */
public static Scalar[] VectorScalar(Scalar[] a, Scalar x)
{
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].mul(x);
}
return result;
}
/* Exponentiate a curve vector by a scalar */
public static Curve25519Point[] VectorScalar2(Curve25519Point[] A, Scalar x)
{
Curve25519Point[] Result = new Curve25519Point[A.length];
for (int i = 0; i < A.length; i++)
{
Result[i] = A[i].scalarMultiply(x);
}
return Result;
}
/* Compute the inverse of a scalar, the stupid way */
public static Scalar Invert(Scalar x)
{
Scalar inverse = new Scalar(x.toBigInteger().modInverse(CryptoUtil.l));
assert x.mul(inverse).equals(Scalar.ONE);
return inverse;
}
/* Compute the slice of a curvepoint vector */
public static Curve25519Point[] CurveSlice(Curve25519Point[] a, int start, int stop)
{
Curve25519Point[] Result = new Curve25519Point[stop-start];
for (int i = start; i < stop; i++)
{
Result[i-start] = a[i];
}
return Result;
}
/* Compute the slice of a scalar vector */
public static Scalar[] ScalarSlice(Scalar[] a, int start, int stop)
{
Scalar[] result = new Scalar[stop-start];
for (int i = start; i < stop; i++)
{
result[i-start] = a[i];
}
return result;
}
/* Given a value v (0..2^N-1) and a mask gamma, construct a range proof */
public static ProofTuple PROVE(Scalar v, Scalar gamma)
{
Curve25519Point V = G.scalarMultiply(v).add(H.scalarMultiply(gamma));
// PAPER LINES 36-37
Scalar[] aL = new Scalar[N];
Scalar[] aR = new Scalar[N];
BigInteger tempV = v.toBigInteger();
for (int i = N-1; i >= 0; i--)
{
BigInteger basePow = BigInteger.valueOf(2).pow(i);
if (tempV.divide(basePow).equals(BigInteger.ZERO))
{
aL[i] = Scalar.ZERO;
}
else
{
aL[i] = Scalar.ONE;
tempV = tempV.subtract(basePow);
}
aR[i] = aL[i].sub(Scalar.ONE);
}
// PAPER LINES 38-39
Scalar alpha = randomScalar();
Curve25519Point A = VectorExponent(aL,aR).add(H.scalarMultiply(alpha));
// PAPER LINES 40-42
Scalar[] sL = new Scalar[N];
Scalar[] sR = new Scalar[N];
for (int i = 0; i < N; i++)
{
sL[i] = randomScalar();
sR[i] = randomScalar();
}
Scalar rho = randomScalar();
Curve25519Point S = VectorExponent(sL,sR).add(H.scalarMultiply(rho));
// PAPER LINES 43-45
Scalar y = hashToScalar(concat(A.toBytes(),S.toBytes()));
Scalar z = hashToScalar(y.bytes);
// Polynomial construction before PAPER LINE 46
Scalar t0 = Scalar.ZERO;
Scalar t1 = Scalar.ZERO;
Scalar t2 = Scalar.ZERO;
t0 = t0.add(z.mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
t0 = t0.add(z.sq().mul(v));
Scalar k = Scalar.ZERO;
k = k.sub(z.sq().mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
k = k.sub(z.pow(3).mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(Scalar.TWO))));
t0 = t0.add(k);
t1 = t1.add(InnerProduct(VectorSubtract(aL,VectorScalar(VectorPowers(Scalar.ONE),z)),Hadamard(VectorPowers(y),sR)));
t1 = t1.add(InnerProduct(sL,VectorAdd(Hadamard(VectorPowers(y),VectorAdd(aR,VectorScalar(VectorPowers(Scalar.ONE),z))),VectorScalar(VectorPowers(Scalar.TWO),z.sq()))));
t2 = t2.add(InnerProduct(sL,Hadamard(VectorPowers(y),sR)));
// PAPER LINES 47-48
Scalar tau1 = randomScalar();
Scalar tau2 = randomScalar();
Curve25519Point T1 = G.scalarMultiply(t1).add(H.scalarMultiply(tau1));
Curve25519Point T2 = G.scalarMultiply(t2).add(H.scalarMultiply(tau2));
// PAPER LINES 49-51
Scalar x = hashToScalar(concat(z.bytes,T1.toBytes(),T2.toBytes()));
// PAPER LINES 52-53
Scalar taux = Scalar.ZERO;
taux = tau1.mul(x);
taux = taux.add(tau2.mul(x.sq()));
taux = taux.add(gamma.mul(z.sq()));
Scalar mu = x.mul(rho).add(alpha);
// PAPER LINES 54-57
Scalar[] l = new Scalar[N];
Scalar[] r = new Scalar[N];
l = VectorAdd(VectorSubtract(aL,VectorScalar(VectorPowers(Scalar.ONE),z)),VectorScalar(sL,x));
r = VectorAdd(Hadamard(VectorPowers(y),VectorAdd(aR,VectorAdd(VectorScalar(VectorPowers(Scalar.ONE),z),VectorScalar(sR,x)))),VectorScalar(VectorPowers(Scalar.TWO),z.sq()));
Scalar t = InnerProduct(l,r);
// PAPER LINES 32-33
Scalar x_ip = hashToScalar(concat(x.bytes,taux.bytes,mu.bytes,t.bytes));
// These are used in the inner product rounds
int nprime = N;
Curve25519Point[] Gprime = new Curve25519Point[N];
Curve25519Point[] Hprime = new Curve25519Point[N];
Scalar[] aprime = new Scalar[N];
Scalar[] bprime = new Scalar[N];
for (int i = 0; i < N; i++)
{
Gprime[i] = Gi[i];
Hprime[i] = Hi[i].scalarMultiply(Invert(y).pow(i));
aprime[i] = l[i];
bprime[i] = r[i];
}
Curve25519Point[] L = new Curve25519Point[logN];
Curve25519Point[] R = new Curve25519Point[logN];
int round = 0; // track the index based on number of rounds
Scalar[] w = new Scalar[logN]; // this is the challenge x in the inner product protocol
// PAPER LINE 13
while (nprime > 1)
{
// PAPER LINE 15
nprime /= 2;
// PAPER LINES 16-17
Scalar cL = InnerProduct(ScalarSlice(aprime,0,nprime),ScalarSlice(bprime,nprime,bprime.length));
Scalar cR = InnerProduct(ScalarSlice(aprime,nprime,aprime.length),ScalarSlice(bprime,0,nprime));
// PAPER LINES 18-19
L[round] = VectorExponentCustom(CurveSlice(Gprime,nprime,Gprime.length),CurveSlice(Hprime,0,nprime),ScalarSlice(aprime,0,nprime),ScalarSlice(bprime,nprime,bprime.length)).add(G.scalarMultiply(cL.mul(x_ip)));
R[round] = VectorExponentCustom(CurveSlice(Gprime,0,nprime),CurveSlice(Hprime,nprime,Hprime.length),ScalarSlice(aprime,nprime,aprime.length),ScalarSlice(bprime,0,nprime)).add(G.scalarMultiply(cR.mul(x_ip)));
// PAPER LINES 21-22
if (round == 0)
w[0] = hashToScalar(concat(L[0].toBytes(),R[0].toBytes()));
else
w[round] = hashToScalar(concat(w[round-1].bytes,L[round].toBytes(),R[round].toBytes()));
// PAPER LINES 24-25
Gprime = Hadamard2(VectorScalar2(CurveSlice(Gprime,0,nprime),Invert(w[round])),VectorScalar2(CurveSlice(Gprime,nprime,Gprime.length),w[round]));
Hprime = Hadamard2(VectorScalar2(CurveSlice(Hprime,0,nprime),w[round]),VectorScalar2(CurveSlice(Hprime,nprime,Hprime.length),Invert(w[round])));
// PAPER LINES 28-29
aprime = VectorAdd(VectorScalar(ScalarSlice(aprime,0,nprime),w[round]),VectorScalar(ScalarSlice(aprime,nprime,aprime.length),Invert(w[round])));
bprime = VectorAdd(VectorScalar(ScalarSlice(bprime,0,nprime),Invert(w[round])),VectorScalar(ScalarSlice(bprime,nprime,bprime.length),w[round]));
round += 1;
}
// PAPER LINE 58 (with inclusions from PAPER LINE 8 and PAPER LINE 20)
return new ProofTuple(V,A,S,T1,T2,taux,mu,L,R,aprime[0],bprime[0],t);
}
/* Given a range proof, determine if it is valid */
public static boolean VERIFY(ProofTuple proof)
{
// Reconstruct the challenges
Scalar y = hashToScalar(concat(proof.A.toBytes(),proof.S.toBytes()));
Scalar z = hashToScalar(y.bytes);
Scalar x = hashToScalar(concat(z.bytes,proof.T1.toBytes(),proof.T2.toBytes()));
Scalar x_ip = hashToScalar(concat(x.bytes,proof.taux.bytes,proof.mu.bytes,proof.t.bytes));
// PAPER LINE 61
Curve25519Point L61Left = H.scalarMultiply(proof.taux).add(G.scalarMultiply(proof.t));
Scalar k = Scalar.ZERO;
k = k.sub(z.sq().mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
k = k.sub(z.pow(3).mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(Scalar.TWO))));
Curve25519Point L61Right = G.scalarMultiply(k.add(z.mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y)))));
L61Right = L61Right.add(proof.V.scalarMultiply(z.sq()));
L61Right = L61Right.add(proof.T1.scalarMultiply(x));
L61Right = L61Right.add(proof.T2.scalarMultiply(x.sq()));
if (!L61Right.equals(L61Left))
return false;
// PAPER LINE 62
Curve25519Point P = Curve25519Point.ZERO;
P = P.add(proof.A);
P = P.add(proof.S.scalarMultiply(x));
Scalar[] Gexp = new Scalar[N];
for (int i = 0; i < N; i++)
Gexp[i] = Scalar.ZERO.sub(z);
Scalar[] Hexp = new Scalar[N];
for (int i = 0; i < N; i++)
{
Hexp[i] = Scalar.ZERO;
Hexp[i] = Hexp[i].add(z.mul(y.pow(i)));
Hexp[i] = Hexp[i].add(z.sq().mul(Scalar.TWO.pow(i)));
Hexp[i] = Hexp[i].mul(Invert(y).pow(i));
}
P = P.add(VectorExponent(Gexp,Hexp));
// Compute the number of rounds for the inner product
int rounds = proof.L.length;
// PAPER LINES 21-22
// The inner product challenges are computed per round
Scalar[] w = new Scalar[rounds];
w[0] = hashToScalar(concat(proof.L[0].toBytes(),proof.R[0].toBytes()));
if (rounds > 1)
{
for (int i = 1; i < rounds; i++)
{
w[i] = hashToScalar(concat(w[i-1].bytes,proof.L[i].toBytes(),proof.R[i].toBytes()));
}
}
// Basically PAPER LINES 24-25
// Compute the curvepoints from G[i] and H[i]
Curve25519Point InnerProdG = Curve25519Point.ZERO;
Curve25519Point InnerProdH = Curve25519Point.ZERO;
for (int i = 0; i < N; i++)
{
// Convert the index to binary IN REVERSE and construct the scalar exponent
int index = i;
Scalar gScalar = Scalar.ONE;
Scalar hScalar = Invert(y).pow(i);
for (int j = rounds-1; j >= 0; j--)
{
int J = w.length - j - 1; // because this is done in reverse bit order
int basePow = (int) Math.pow(2,j); // assumes we don't get too big
if (index / basePow == 0) // bit is zero
{
gScalar = gScalar.mul(Invert(w[J]));
hScalar = hScalar.mul(w[J]);
}
else // bit is one
{
gScalar = gScalar.mul(w[J]);
hScalar = hScalar.mul(Invert(w[J]));
index -= basePow;
}
}
// Now compute the basepoint's scalar multiplication
// Each of these could be written as a multiexp operation instead
InnerProdG = InnerProdG.add(Gi[i].scalarMultiply(gScalar));
InnerProdH = InnerProdH.add(Hi[i].scalarMultiply(hScalar));
}
// PAPER LINE 26
Curve25519Point Pprime = P.add(H.scalarMultiply(Scalar.ZERO.sub(proof.mu)));
for (int i = 0; i < rounds; i++)
{
Pprime = Pprime.add(proof.L[i].scalarMultiply(w[i].sq()));
Pprime = Pprime.add(proof.R[i].scalarMultiply(Invert(w[i]).sq()));
}
Pprime = Pprime.add(G.scalarMultiply(proof.t.mul(x_ip)));
if (!Pprime.equals(InnerProdG.scalarMultiply(proof.a).add(InnerProdH.scalarMultiply(proof.b)).add(G.scalarMultiply(proof.a.mul(proof.b).mul(x_ip)))))
return false;
return true;
}
public static void main(String[] args)
{
// Number of bits in the range
N = 64;
logN = 6; // its log, manually
// Set the curve base points
G = Curve25519Point.G;
H = Curve25519Point.hashToPoint(G);
Gi = new Curve25519Point[N];
Hi = new Curve25519Point[N];
for (int i = 0; i < N; i++)
{
Gi[i] = getHpnGLookup(i);
Hi[i] = getHpnGLookup(N+i);
}
// Run a bunch of randomized trials
Random rando = new Random();
int TRIALS = 250;
int count = 0;
while (count < TRIALS)
{
long amount = rando.nextLong();
if (amount > Math.pow(2,N)-1 || amount < 0)
continue;
ProofTuple proof = PROVE(new Scalar(BigInteger.valueOf(amount)),randomScalar());
if (!VERIFY(proof))
System.out.println("Test failed");
count += 1;
}
}
}

View file

@ -0,0 +1,487 @@
package how.monero.hodl.bulletproof;
import how.monero.hodl.crypto.Curve25519Point;
import how.monero.hodl.crypto.Scalar;
import how.monero.hodl.crypto.CryptoUtil;
import java.math.BigInteger;
import java.util.Random;
import static how.monero.hodl.crypto.Scalar.randomScalar;
import static how.monero.hodl.crypto.CryptoUtil.*;
import static how.monero.hodl.util.ByteUtil.*;
public class OptimizedLogBulletproof
{
private static int N;
private static int logN;
private static Curve25519Point G;
private static Curve25519Point H;
private static Curve25519Point[] Gi;
private static Curve25519Point[] Hi;
public static class ProofTuple
{
private Curve25519Point V;
private Curve25519Point A;
private Curve25519Point S;
private Curve25519Point T1;
private Curve25519Point T2;
private Scalar taux;
private Scalar mu;
private Curve25519Point[] L;
private Curve25519Point[] R;
private Scalar a;
private Scalar b;
private Scalar t;
public ProofTuple(Curve25519Point V, Curve25519Point A, Curve25519Point S, Curve25519Point T1, Curve25519Point T2, Scalar taux, Scalar mu, Curve25519Point[] L, Curve25519Point[] R, Scalar a, Scalar b, Scalar t)
{
this.V = V;
this.A = A;
this.S = S;
this.T1 = T1;
this.T2 = T2;
this.taux = taux;
this.mu = mu;
this.L = L;
this.R = R;
this.a = a;
this.b = b;
this.t = t;
}
}
/* Given two scalar arrays, construct a vector commitment */
public static Curve25519Point VectorExponent(Scalar[] a, Scalar[] b)
{
assert a.length == N && b.length == N;
Curve25519Point Result = Curve25519Point.ZERO;
for (int i = 0; i < N; i++)
{
Result = Result.add(Gi[i].scalarMultiply(a[i]));
Result = Result.add(Hi[i].scalarMultiply(b[i]));
}
return Result;
}
/* Compute a custom vector-scalar commitment */
public static Curve25519Point VectorExponentCustom(Curve25519Point[] A, Curve25519Point[] B, Scalar[] a, Scalar[] b)
{
assert a.length == A.length && b.length == B.length && a.length == b.length;
Curve25519Point Result = Curve25519Point.ZERO;
for (int i = 0; i < a.length; i++)
{
Result = Result.add(A[i].scalarMultiply(a[i]));
Result = Result.add(B[i].scalarMultiply(b[i]));
}
return Result;
}
/* Given a scalar, construct a vector of powers */
public static Scalar[] VectorPowers(Scalar x)
{
Scalar[] result = new Scalar[N];
for (int i = 0; i < N; i++)
{
result[i] = x.pow(i);
}
return result;
}
/* Given two scalar arrays, construct the inner product */
public static Scalar InnerProduct(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar result = Scalar.ZERO;
for (int i = 0; i < a.length; i++)
{
result = result.add(a[i].mul(b[i]));
}
return result;
}
/* Given two scalar arrays, construct the Hadamard product */
public static Scalar[] Hadamard(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].mul(b[i]);
}
return result;
}
/* Given two curvepoint arrays, construct the Hadamard product */
public static Curve25519Point[] Hadamard2(Curve25519Point[] A, Curve25519Point[] B)
{
assert A.length == B.length;
Curve25519Point[] Result = new Curve25519Point[A.length];
for (int i = 0; i < A.length; i++)
{
Result[i] = A[i].add(B[i]);
}
return Result;
}
/* Add two vectors */
public static Scalar[] VectorAdd(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].add(b[i]);
}
return result;
}
/* Subtract two vectors */
public static Scalar[] VectorSubtract(Scalar[] a, Scalar[] b)
{
assert a.length == b.length;
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].sub(b[i]);
}
return result;
}
/* Multiply a scalar and a vector */
public static Scalar[] VectorScalar(Scalar[] a, Scalar x)
{
Scalar[] result = new Scalar[a.length];
for (int i = 0; i < a.length; i++)
{
result[i] = a[i].mul(x);
}
return result;
}
/* Exponentiate a curve vector by a scalar */
public static Curve25519Point[] VectorScalar2(Curve25519Point[] A, Scalar x)
{
Curve25519Point[] Result = new Curve25519Point[A.length];
for (int i = 0; i < A.length; i++)
{
Result[i] = A[i].scalarMultiply(x);
}
return Result;
}
/* Compute the inverse of a scalar, the stupid way */
public static Scalar Invert(Scalar x)
{
Scalar inverse = new Scalar(x.toBigInteger().modInverse(CryptoUtil.l));
assert x.mul(inverse).equals(Scalar.ONE);
return inverse;
}
/* Compute the slice of a curvepoint vector */
public static Curve25519Point[] CurveSlice(Curve25519Point[] a, int start, int stop)
{
Curve25519Point[] Result = new Curve25519Point[stop-start];
for (int i = start; i < stop; i++)
{
Result[i-start] = a[i];
}
return Result;
}
/* Compute the slice of a scalar vector */
public static Scalar[] ScalarSlice(Scalar[] a, int start, int stop)
{
Scalar[] result = new Scalar[stop-start];
for (int i = start; i < stop; i++)
{
result[i-start] = a[i];
}
return result;
}
/* Given a value v (0..2^N-1) and a mask gamma, construct a range proof */
public static ProofTuple PROVE(Scalar v, Scalar gamma)
{
Curve25519Point V = G.scalarMultiply(v).add(H.scalarMultiply(gamma));
// PAPER LINES 36-37
Scalar[] aL = new Scalar[N];
Scalar[] aR = new Scalar[N];
BigInteger tempV = v.toBigInteger();
for (int i = N-1; i >= 0; i--)
{
BigInteger basePow = BigInteger.valueOf(2).pow(i);
if (tempV.divide(basePow).equals(BigInteger.ZERO))
{
aL[i] = Scalar.ZERO;
}
else
{
aL[i] = Scalar.ONE;
tempV = tempV.subtract(basePow);
}
aR[i] = aL[i].sub(Scalar.ONE);
}
// PAPER LINES 38-39
Scalar alpha = randomScalar();
Curve25519Point A = VectorExponent(aL,aR).add(H.scalarMultiply(alpha));
// PAPER LINES 40-42
Scalar[] sL = new Scalar[N];
Scalar[] sR = new Scalar[N];
for (int i = 0; i < N; i++)
{
sL[i] = randomScalar();
sR[i] = randomScalar();
}
Scalar rho = randomScalar();
Curve25519Point S = VectorExponent(sL,sR).add(H.scalarMultiply(rho));
// PAPER LINES 43-45
Scalar y = hashToScalar(concat(A.toBytes(),S.toBytes()));
Scalar z = hashToScalar(y.bytes);
// Polynomial construction before PAPER LINE 46
Scalar t0 = Scalar.ZERO;
Scalar t1 = Scalar.ZERO;
Scalar t2 = Scalar.ZERO;
t0 = t0.add(z.mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
t0 = t0.add(z.sq().mul(v));
Scalar k = Scalar.ZERO;
k = k.sub(z.sq().mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
k = k.sub(z.pow(3).mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(Scalar.TWO))));
t0 = t0.add(k);
t1 = t1.add(InnerProduct(VectorSubtract(aL,VectorScalar(VectorPowers(Scalar.ONE),z)),Hadamard(VectorPowers(y),sR)));
t1 = t1.add(InnerProduct(sL,VectorAdd(Hadamard(VectorPowers(y),VectorAdd(aR,VectorScalar(VectorPowers(Scalar.ONE),z))),VectorScalar(VectorPowers(Scalar.TWO),z.sq()))));
t2 = t2.add(InnerProduct(sL,Hadamard(VectorPowers(y),sR)));
// PAPER LINES 47-48
Scalar tau1 = randomScalar();
Scalar tau2 = randomScalar();
Curve25519Point T1 = G.scalarMultiply(t1).add(H.scalarMultiply(tau1));
Curve25519Point T2 = G.scalarMultiply(t2).add(H.scalarMultiply(tau2));
// PAPER LINES 49-51
Scalar x = hashToScalar(concat(z.bytes,T1.toBytes(),T2.toBytes()));
// PAPER LINES 52-53
Scalar taux = Scalar.ZERO;
taux = tau1.mul(x);
taux = taux.add(tau2.mul(x.sq()));
taux = taux.add(gamma.mul(z.sq()));
Scalar mu = x.mul(rho).add(alpha);
// PAPER LINES 54-57
Scalar[] l = new Scalar[N];
Scalar[] r = new Scalar[N];
l = VectorAdd(VectorSubtract(aL,VectorScalar(VectorPowers(Scalar.ONE),z)),VectorScalar(sL,x));
r = VectorAdd(Hadamard(VectorPowers(y),VectorAdd(aR,VectorAdd(VectorScalar(VectorPowers(Scalar.ONE),z),VectorScalar(sR,x)))),VectorScalar(VectorPowers(Scalar.TWO),z.sq()));
Scalar t = InnerProduct(l,r);
// PAPER LINES 32-33
Scalar x_ip = hashToScalar(concat(x.bytes,taux.bytes,mu.bytes,t.bytes));
// These are used in the inner product rounds
int nprime = N;
Curve25519Point[] Gprime = new Curve25519Point[N];
Curve25519Point[] Hprime = new Curve25519Point[N];
Scalar[] aprime = new Scalar[N];
Scalar[] bprime = new Scalar[N];
for (int i = 0; i < N; i++)
{
Gprime[i] = Gi[i];
Hprime[i] = Hi[i].scalarMultiply(Invert(y).pow(i));
aprime[i] = l[i];
bprime[i] = r[i];
}
Curve25519Point[] L = new Curve25519Point[logN];
Curve25519Point[] R = new Curve25519Point[logN];
int round = 0; // track the index based on number of rounds
Scalar[] w = new Scalar[logN]; // this is the challenge x in the inner product protocol
// PAPER LINE 13
while (nprime > 1)
{
// PAPER LINE 15
nprime /= 2;
// PAPER LINES 16-17
Scalar cL = InnerProduct(ScalarSlice(aprime,0,nprime),ScalarSlice(bprime,nprime,bprime.length));
Scalar cR = InnerProduct(ScalarSlice(aprime,nprime,aprime.length),ScalarSlice(bprime,0,nprime));
// PAPER LINES 18-19
L[round] = VectorExponentCustom(CurveSlice(Gprime,nprime,Gprime.length),CurveSlice(Hprime,0,nprime),ScalarSlice(aprime,0,nprime),ScalarSlice(bprime,nprime,bprime.length)).add(G.scalarMultiply(cL.mul(x_ip)));
R[round] = VectorExponentCustom(CurveSlice(Gprime,0,nprime),CurveSlice(Hprime,nprime,Hprime.length),ScalarSlice(aprime,nprime,aprime.length),ScalarSlice(bprime,0,nprime)).add(G.scalarMultiply(cR.mul(x_ip)));
// PAPER LINES 21-22
if (round == 0)
w[0] = hashToScalar(concat(L[0].toBytes(),R[0].toBytes()));
else
w[round] = hashToScalar(concat(w[round-1].bytes,L[round].toBytes(),R[round].toBytes()));
// PAPER LINES 24-25
Gprime = Hadamard2(VectorScalar2(CurveSlice(Gprime,0,nprime),Invert(w[round])),VectorScalar2(CurveSlice(Gprime,nprime,Gprime.length),w[round]));
Hprime = Hadamard2(VectorScalar2(CurveSlice(Hprime,0,nprime),w[round]),VectorScalar2(CurveSlice(Hprime,nprime,Hprime.length),Invert(w[round])));
// PAPER LINES 28-29
aprime = VectorAdd(VectorScalar(ScalarSlice(aprime,0,nprime),w[round]),VectorScalar(ScalarSlice(aprime,nprime,aprime.length),Invert(w[round])));
bprime = VectorAdd(VectorScalar(ScalarSlice(bprime,0,nprime),Invert(w[round])),VectorScalar(ScalarSlice(bprime,nprime,bprime.length),w[round]));
round += 1;
}
// PAPER LINE 58 (with inclusions from PAPER LINE 8 and PAPER LINE 20)
return new ProofTuple(V,A,S,T1,T2,taux,mu,L,R,aprime[0],bprime[0],t);
}
/* Given a range proof, determine if it is valid */
public static boolean VERIFY(ProofTuple proof)
{
// Reconstruct the challenges
Scalar y = hashToScalar(concat(proof.A.toBytes(),proof.S.toBytes()));
Scalar z = hashToScalar(y.bytes);
Scalar x = hashToScalar(concat(z.bytes,proof.T1.toBytes(),proof.T2.toBytes()));
Scalar x_ip = hashToScalar(concat(x.bytes,proof.taux.bytes,proof.mu.bytes,proof.t.bytes));
// PAPER LINE 61
Curve25519Point L61Left = H.scalarMultiply(proof.taux).add(G.scalarMultiply(proof.t));
Scalar k = Scalar.ZERO;
k = k.sub(z.sq().mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y))));
k = k.sub(z.pow(3).mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(Scalar.TWO))));
Curve25519Point L61Right = G.scalarMultiply(k.add(z.mul(InnerProduct(VectorPowers(Scalar.ONE),VectorPowers(y)))));
L61Right = L61Right.add(proof.V.scalarMultiply(z.sq()));
L61Right = L61Right.add(proof.T1.scalarMultiply(x));
L61Right = L61Right.add(proof.T2.scalarMultiply(x.sq()));
if (!L61Right.equals(L61Left))
return false;
// PAPER LINE 62
Curve25519Point P = Curve25519Point.ZERO;
P = P.add(proof.A);
P = P.add(proof.S.scalarMultiply(x));
// Compute the number of rounds for the inner product
int rounds = proof.L.length;
// PAPER LINES 21-22
// The inner product challenges are computed per round
Scalar[] w = new Scalar[rounds];
w[0] = hashToScalar(concat(proof.L[0].toBytes(),proof.R[0].toBytes()));
if (rounds > 1)
{
for (int i = 1; i < rounds; i++)
{
w[i] = hashToScalar(concat(w[i-1].bytes,proof.L[i].toBytes(),proof.R[i].toBytes()));
}
}
// Basically PAPER LINES 24-25
// Compute the curvepoints from G[i] and H[i]
Curve25519Point InnerProdG = Curve25519Point.ZERO;
Curve25519Point InnerProdH = Curve25519Point.ZERO;
for (int i = 0; i < N; i++)
{
// Convert the index to binary IN REVERSE and construct the scalar exponent
int index = i;
Scalar gScalar = proof.a;
Scalar hScalar = proof.b.mul(Invert(y).pow(i));
for (int j = rounds-1; j >= 0; j--)
{
int J = w.length - j - 1; // because this is done in reverse bit order
int basePow = (int) Math.pow(2,j); // assumes we don't get too big
if (index / basePow == 0) // bit is zero
{
gScalar = gScalar.mul(Invert(w[J]));
hScalar = hScalar.mul(w[J]);
}
else // bit is one
{
gScalar = gScalar.mul(w[J]);
hScalar = hScalar.mul(Invert(w[J]));
index -= basePow;
}
}
// Adjust the scalars using the exponents from PAPER LINE 62
gScalar = gScalar.add(z);
hScalar = hScalar.sub(z.mul(y.pow(i)).add(z.sq().mul(Scalar.TWO.pow(i))).mul(Invert(y).pow(i)));
// Now compute the basepoint's scalar multiplication
// Each of these could be written as a multiexp operation instead
InnerProdG = InnerProdG.add(Gi[i].scalarMultiply(gScalar));
InnerProdH = InnerProdH.add(Hi[i].scalarMultiply(hScalar));
}
// PAPER LINE 26
Curve25519Point Pprime = P.add(H.scalarMultiply(Scalar.ZERO.sub(proof.mu)));
for (int i = 0; i < rounds; i++)
{
Pprime = Pprime.add(proof.L[i].scalarMultiply(w[i].sq()));
Pprime = Pprime.add(proof.R[i].scalarMultiply(Invert(w[i]).sq()));
}
Pprime = Pprime.add(G.scalarMultiply(proof.t.mul(x_ip)));
if (!Pprime.equals(InnerProdG.add(InnerProdH).add(G.scalarMultiply(proof.a.mul(proof.b).mul(x_ip)))))
return false;
return true;
}
public static void main(String[] args)
{
// Number of bits in the range
N = 64;
logN = 6; // its log, manually
// Set the curve base points
G = Curve25519Point.G;
H = Curve25519Point.hashToPoint(G);
Gi = new Curve25519Point[N];
Hi = new Curve25519Point[N];
for (int i = 0; i < N; i++)
{
Gi[i] = getHpnGLookup(i);
Hi[i] = getHpnGLookup(N+i);
}
// Run a bunch of randomized trials
Random rando = new Random();
int TRIALS = 250;
int count = 0;
while (count < TRIALS)
{
long amount = rando.nextLong();
if (amount > Math.pow(2,N)-1 || amount < 0)
continue;
ProofTuple proof = PROVE(new Scalar(BigInteger.valueOf(amount)),randomScalar());
if (!VERIFY(proof))
System.out.println("Test failed");
count += 1;
}
}
}