1 files changed, 170 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/signers/DSTU4145Signer.java b/core/src/main/java/org/spongycastle/crypto/signers/DSTU4145Signer.java
new file mode 100644
index 00000000..f938f5cf
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/signers/DSTU4145Signer.java
@@ -0,0 +1,170 @@
+package org.spongycastle.crypto.signers;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.CipherParameters;
+import org.spongycastle.crypto.DSA;
+import org.spongycastle.crypto.params.ECDomainParameters;
+import org.spongycastle.crypto.params.ECKeyParameters;
+import org.spongycastle.crypto.params.ECPrivateKeyParameters;
+import org.spongycastle.crypto.params.ECPublicKeyParameters;
+import org.spongycastle.crypto.params.ParametersWithRandom;
+import org.spongycastle.math.ec.ECAlgorithms;
+import org.spongycastle.math.ec.ECCurve;
+import org.spongycastle.math.ec.ECFieldElement;
+import org.spongycastle.math.ec.ECMultiplier;
+import org.spongycastle.math.ec.ECPoint;
+import org.spongycastle.math.ec.FixedPointCombMultiplier;
+import org.spongycastle.util.Arrays;
+
+/**
+ * DSTU 4145-2002
+ * <p>
+ * National Ukrainian standard of digital signature based on elliptic curves (DSTU 4145-2002).
+ * </p>
+ */
+public class DSTU4145Signer
+    implements DSA
+{
+    private static final BigInteger ONE = BigInteger.valueOf(1);
+
+    private ECKeyParameters key;
+    private SecureRandom random;
+
+    public void init(boolean forSigning, CipherParameters param)
+    {
+        if (forSigning)
+        {
+            if (param instanceof ParametersWithRandom)
+            {
+                ParametersWithRandom rParam = (ParametersWithRandom)param;
+
+                this.random = rParam.getRandom();
+                param = rParam.getParameters();
+            }
+            else
+            {
+                this.random = new SecureRandom();
+            }
+
+            this.key = (ECPrivateKeyParameters)param;
+        }
+        else
+        {
+            this.key = (ECPublicKeyParameters)param;
+        }
+
+    }
+
+    public BigInteger[] generateSignature(byte[] message)
+    {
+        ECDomainParameters ec = key.getParameters();
+
+        ECCurve curve = ec.getCurve();
+
+        ECFieldElement h = hash2FieldElement(curve, message);
+        if (h.isZero())
+        {
+            h = curve.fromBigInteger(ONE);
+        }
+
+        BigInteger n = ec.getN();
+        BigInteger e, r, s;
+        ECFieldElement Fe, y;
+
+        BigInteger d = ((ECPrivateKeyParameters)key).getD();
+
+        ECMultiplier basePointMultiplier = createBasePointMultiplier();
+
+        do
+        {
+            do
+            {
+                do
+                {
+                    e = generateRandomInteger(n, random);
+                    Fe = basePointMultiplier.multiply(ec.getG(), e).normalize().getAffineXCoord();
+                }
+                while (Fe.isZero());
+
+                y = h.multiply(Fe);
+                r = fieldElement2Integer(n, y);
+            }
+            while (r.signum() == 0);
+
+            s = r.multiply(d).add(e).mod(n);
+        }
+        while (s.signum() == 0);
+
+        return new BigInteger[]{r, s};
+    }
+
+    public boolean verifySignature(byte[] message, BigInteger r, BigInteger s)
+    {
+        if (r.signum() <= 0 || s.signum() <= 0)
+        {
+            return false;
+        }
+
+        ECDomainParameters parameters = key.getParameters();
+
+        BigInteger n = parameters.getN();
+        if (r.compareTo(n) >= 0 || s.compareTo(n) >= 0)
+        {
+            return false;
+        }
+
+        ECCurve curve = parameters.getCurve();
+
+        ECFieldElement h = hash2FieldElement(curve, message);
+        if (h.isZero())
+        {
+            h = curve.fromBigInteger(ONE);
+        }
+
+        ECPoint R = ECAlgorithms.sumOfTwoMultiplies(parameters.getG(), s, ((ECPublicKeyParameters)key).getQ(), r).normalize();
+
+        // components must be bogus.
+        if (R.isInfinity())
+        {
+            return false;
+        }
+
+        ECFieldElement y = h.multiply(R.getAffineXCoord());
+        return fieldElement2Integer(n, y).compareTo(r) == 0;
+    }
+
+    protected ECMultiplier createBasePointMultiplier()
+    {
+        return new FixedPointCombMultiplier();
+    }
+
+    /**
+     * Generates random integer such, than its bit length is less than that of n
+     */
+    private static BigInteger generateRandomInteger(BigInteger n, SecureRandom random)
+    {
+        return new BigInteger(n.bitLength() - 1, random);
+    }
+
+    private static ECFieldElement hash2FieldElement(ECCurve curve, byte[] hash)
+    {
+        byte[] data = Arrays.reverse(hash);
+        return curve.fromBigInteger(truncate(new BigInteger(1, data), curve.getFieldSize()));
+    }
+
+    private static BigInteger fieldElement2Integer(BigInteger n, ECFieldElement fe)
+    {
+        return truncate(fe.toBigInteger(), n.bitLength() - 1);
+    }
+
+    private static BigInteger truncate(BigInteger x, int bitLength)
+    {
+        if (x.bitLength() > bitLength)
+        {
+            x = x.mod(ONE.shiftLeft(bitLength));
+        }
+        return x;
+    }
+}