diff options
Diffstat (limited to 'src/cz/crcs/ectester/common/util/ECUtil.java')
| -rw-r--r-- | src/cz/crcs/ectester/common/util/ECUtil.java | 31 |
1 files changed, 30 insertions, 1 deletions
diff --git a/src/cz/crcs/ectester/common/util/ECUtil.java b/src/cz/crcs/ectester/common/util/ECUtil.java index 75a75fc..4736f23 100644 --- a/src/cz/crcs/ectester/common/util/ECUtil.java +++ b/src/cz/crcs/ectester/common/util/ECUtil.java @@ -20,6 +20,7 @@ import java.security.interfaces.ECKey; import java.security.interfaces.ECPrivateKey; import java.security.interfaces.ECPublicKey; import java.security.spec.*; +import java.util.Random; /** * @author Jan Jancar johny@neuromancer.sk @@ -97,7 +98,7 @@ public class ECUtil { 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; + return result.equals(BigInteger.ONE); } private static BigInteger modSqrt(BigInteger a, BigInteger p) { @@ -329,4 +330,32 @@ public class ECUtil { } return null; } + + public static EC_Params randomPoint(EllipticCurve curve) { + BigInteger x; + BigInteger p; + if (curve.getField() instanceof ECFieldFp) { + ECFieldFp fp = (ECFieldFp) curve.getField(); + p = fp.getP(); + } else { + //TODO + throw new UnsupportedOperationException(); + } + BigInteger rhs; + Random rand = new Random(); + do { + x = new BigInteger(curve.getField().getFieldSize(), rand); + x = x.mod(p); + rhs = x.modPow(BigInteger.valueOf(3), p); + rhs = rhs.add(curve.getA().multiply(x)).mod(p); + rhs = rhs.add(curve.getB()).mod(p); + } while (!isResidue(rhs, p)); + BigInteger y = modSqrt(rhs, p); + if (rand.nextBoolean()) { + y = p.subtract(y); + } + byte[] xArr = toByteArray(x, curve.getField().getFieldSize()); + byte[] yArr = toByteArray(y, curve.getField().getFieldSize()); + return new EC_Params(EC_Consts.PARAMETER_W, new byte[][]{xArr, yArr}); + } } |