Hi Fabrizio,
All those divisions should be modular divisions. To perform a modular
division using BigInteger you use the ModInverse method:
x / y mod m => y.ModInverse(m).Multiply(x).Mod(m)
Regards,
Pete Dettman
On 3/01/2024 8:41 pm, Fabrizio Lieggi wrote:
Hi everyone,
I’m starting to learn the BouncyCastle C# lib use, can anybody help
me with this code:
publicstaticECDomainParameters BabyJubJubDomainParameters()
{
// EC parameters (Montgomery Form)
// values from https://eips.ethereum.org/EIPS/eip-2494
varp =
newOrg.BouncyCastle.Math.BigInteger("21888242871839275222246405745257275088548364400416034343698204186575808495617");
varh = newOrg.BouncyCastle.Math.BigInteger("8");
varn =
newOrg.BouncyCastle.Math.BigInteger("21888242871839275222246405745257275088614511777268538073601725287587578984328");
vara = newOrg.BouncyCastle.Math.BigInteger("168698");
varb = newOrg.BouncyCastle.Math.BigInteger("1");
varM_GX = newOrg.BouncyCastle.Math.BigInteger("7");
varM_GY =
newOrg.BouncyCastle.Math.BigInteger("4258727773875940690362607550498304598101071202821725296872974770776423442226");
varorder = n.Multiply(h);
/*
https://upcommons.upc.edu/bitstream/handle/2117/361741/mathematics-09-03022.pdf?sequence=1
# Transform a Montgomery curve to a short Weierstrass .
a = (3 - A^2) / (3 * B^2)
b = (2 * A^3 - 9*A) / (27 * B^3)
x0,y0 = (x0 + A/3) / B , y0 / B
x1,y1 = (x1 + A/3) / B , y1 / B
*/
varnove = newOrg.BouncyCastle.Math.BigInteger("9");
varW_a =
((Org.BouncyCastle.Math.BigInteger.Three.Subtract(a.Pow(2))).Divide(Org.BouncyCastle.Math.BigInteger.Three.Multiply(b.Pow(2)))).Mod(p);
varW_b =
(Org.BouncyCastle.Math.BigInteger.Two.Multiply(a.Pow(3)).Subtract(nove.Multiply(a))).Divide((newOrg.BouncyCastle.Math.BigInteger("27")).Multiply(b.Pow(3)));
//.Mod(p);
varW_GX =
(M_GX.Add(a.Divide(Org.BouncyCastle.Math.BigInteger.Three))).Divide(b);
//.Mod(p);
varW_GY = M_GY.Divide(b); //.Mod(p);
Org.BouncyCastle.Math.EC.ECCurve curve = newFpCurve(p, W_a, W_b, n, h);
Org.BouncyCastle.Math.EC.ECPoint generatorPoint =
curve.CreatePoint(W_GX, W_GY);
returnnewECDomainParameters(curve, generatorPoint, n, h);
}
varecParameters = CryptoUtils.BabyJubJubDomainParameters();
The internal method ValidatePublicPoint of the class
ECDomainParameters returns an exception:
*System.ArgumentException:*'Point not on curve (Parameter 'q')'
Thanks in advance,
Best regards
F
