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package cz.crcs.ectester.common.util;
import java.math.BigInteger;
import java.security.spec.*;
/**
* @author Jan Jancar johny@neuromancer.sk
*/
public class ECUtil {
public static byte[] toX962Compressed(ECPoint point) {
if (point.equals(ECPoint.POINT_INFINITY)) {
return new byte[]{0};
}
byte[] x = point.getAffineX().toByteArray();
byte marker = (byte) (0x02 | point.getAffineY().mod(BigInteger.valueOf(2)).byteValue());
return ByteUtil.concatenate(new byte[]{marker}, x);
}
public static byte[] toX962Uncompressed(ECPoint point) {
if (point.equals(ECPoint.POINT_INFINITY)) {
return new byte[]{0};
}
byte[] x = point.getAffineX().toByteArray();
byte[] y = point.getAffineY().toByteArray();
return ByteUtil.concatenate(new byte[]{0x04}, x, y);
}
public static byte[] toX962Hybrid(ECPoint point) {
if (point.equals(ECPoint.POINT_INFINITY)) {
return new byte[]{0};
}
byte[] x = point.getAffineX().toByteArray();
byte[] y = point.getAffineY().toByteArray();
byte marker = (byte) (0x06 | point.getAffineY().mod(BigInteger.valueOf(2)).byteValue());
return ByteUtil.concatenate(new byte[]{marker}, x, y);
}
private static boolean isResidue(BigInteger a, BigInteger p) {
BigInteger exponent = p.subtract(BigInteger.ONE).divide(BigInteger.valueOf(2));
BigInteger result = a.modPow(exponent, p);
return result.intValueExact() == 1;
}
private static BigInteger modSqrt(BigInteger a, BigInteger p) {
BigInteger q = p.subtract(BigInteger.ONE);
int s = 0;
while (q.mod(BigInteger.valueOf(2)).equals(BigInteger.ZERO)) {
q = q.divide(BigInteger.valueOf(2));
s++;
}
BigInteger z = BigInteger.ONE;
do {
z = z.add(BigInteger.ONE);
} while (isResidue(z, p));
BigInteger m = BigInteger.valueOf(s);
BigInteger c = z.modPow(q, p);
BigInteger t = a.modPow(q, p);
BigInteger rExponent = q.add(BigInteger.ONE).divide(BigInteger.valueOf(2));
BigInteger r = a.modPow(rExponent, p);
while (!t.equals(BigInteger.ONE)) {
int i = 0;
BigInteger exponent;
do {
exponent = BigInteger.valueOf(2).pow(++i);
} while (!t.modPow(exponent, p).equals(BigInteger.ONE));
BigInteger twoExponent = m.subtract(BigInteger.valueOf(i + 1));
BigInteger b = c.modPow(BigInteger.valueOf(2).modPow(twoExponent, p), p);
m = BigInteger.valueOf(i);
c = b.modPow(BigInteger.valueOf(2), p);
t = t.multiply(c).mod(p);
r = r.multiply(b).mod(p);
}
return r;
}
public static ECPoint fromX962(byte[] data, EllipticCurve curve) {
if (data == null) {
return null;
}
if (data[0] == 0x04 || data[0] == 0x06 || data[0] == 0x07) {
int len = (data.length - 1) / 2;
byte[] xbytes = new byte[len];
System.arraycopy(data, 1, xbytes, 0, len);
byte[] ybytes = new byte[len];
System.arraycopy(data, 1 + len, ybytes, 0, len);
return new ECPoint(new BigInteger(xbytes), new BigInteger(ybytes));
} else if (data[0] == 0x02 || data[0] == 0x03) {
if (curve == null) {
throw new IllegalArgumentException();
}
byte[] xbytes = new byte[data.length - 1];
System.arraycopy(data, 1, xbytes, 0, data.length - 1);
BigInteger x = new BigInteger(xbytes);
BigInteger a = curve.getA();
BigInteger b = curve.getB();
ECField field = curve.getField();
if (field instanceof ECFieldFp) {
BigInteger p = ((ECFieldFp) field).getP();
BigInteger alpha = x.modPow(BigInteger.valueOf(3), p);
alpha = alpha.add(x.multiply(a));
alpha = alpha.add(b);
BigInteger beta = modSqrt(alpha, p);
if (beta.getLowestSetBit() == 0) {
// rightmost bit is one
if (data[0] == 0x02) {
beta = beta.negate();
}
} else {
// rightmost bit is zero
if (data[0] == 0x03) {
beta = beta.negate();
}
}
return new ECPoint(x, beta);
} else if (field instanceof ECFieldF2m) {
}
return null;
} else {
throw new IllegalArgumentException();
}
}
}
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