1 files changed, 69 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/generators/DSAKeyPairGenerator.java b/core/src/main/java/org/spongycastle/crypto/generators/DSAKeyPairGenerator.java
new file mode 100644
index 00000000..01c3b26a
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/generators/DSAKeyPairGenerator.java
@@ -0,0 +1,69 @@
+package org.spongycastle.crypto.generators;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.AsymmetricCipherKeyPair;
+import org.spongycastle.crypto.AsymmetricCipherKeyPairGenerator;
+import org.spongycastle.crypto.KeyGenerationParameters;
+import org.spongycastle.crypto.params.DSAKeyGenerationParameters;
+import org.spongycastle.crypto.params.DSAParameters;
+import org.spongycastle.crypto.params.DSAPrivateKeyParameters;
+import org.spongycastle.crypto.params.DSAPublicKeyParameters;
+import org.spongycastle.math.ec.WNafUtil;
+import org.spongycastle.util.BigIntegers;
+
+/**
+ * a DSA key pair generator.
+ *
+ * This generates DSA keys in line with the method described 
+ * in <i>FIPS 186-3 B.1 FFC Key Pair Generation</i>.
+ */
+public class DSAKeyPairGenerator
+    implements AsymmetricCipherKeyPairGenerator
+{
+    private static final BigInteger ONE = BigInteger.valueOf(1);
+
+    private DSAKeyGenerationParameters param;
+
+    public void init(
+        KeyGenerationParameters param)
+    {
+        this.param = (DSAKeyGenerationParameters)param;
+    }
+
+    public AsymmetricCipherKeyPair generateKeyPair()
+    {
+        DSAParameters dsaParams = param.getParameters();
+
+        BigInteger x = generatePrivateKey(dsaParams.getQ(), param.getRandom());
+        BigInteger y = calculatePublicKey(dsaParams.getP(), dsaParams.getG(), x);
+
+        return new AsymmetricCipherKeyPair(
+            new DSAPublicKeyParameters(y, dsaParams),
+            new DSAPrivateKeyParameters(x, dsaParams));
+    }
+
+    private static BigInteger generatePrivateKey(BigInteger q, SecureRandom random)
+    {
+        // B.1.2 Key Pair Generation by Testing Candidates
+        int minWeight = q.bitLength() >>> 2;
+        for (;;)
+        {
+            // TODO Prefer this method? (change test cases that used fixed random)
+            // B.1.1 Key Pair Generation Using Extra Random Bits
+//            BigInteger x = new BigInteger(q.bitLength() + 64, random).mod(q.subtract(ONE)).add(ONE);
+
+            BigInteger x = BigIntegers.createRandomInRange(ONE, q.subtract(ONE), random);
+            if (WNafUtil.getNafWeight(x) >= minWeight)
+            {
+                return x;
+            }
+        }
+    }
+
+    private static BigInteger calculatePublicKey(BigInteger p, BigInteger g, BigInteger x)
+    {
+        return g.modPow(x, p);
+    }
+}