1 files changed, 51 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/generators/DHKeyGeneratorHelper.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/generators/DHKeyGeneratorHelper.java
new file mode 100644
index 000000000..b987e5b1c
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/generators/DHKeyGeneratorHelper.java
@@ -0,0 +1,51 @@
+package org.spongycastle.crypto.generators;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.params.DHParameters;
+import org.spongycastle.util.BigIntegers;
+
+class DHKeyGeneratorHelper
+{
+    static final DHKeyGeneratorHelper INSTANCE = new DHKeyGeneratorHelper();
+
+    private static final BigInteger ONE = BigInteger.valueOf(1);
+    private static final BigInteger TWO = BigInteger.valueOf(2);
+
+    private DHKeyGeneratorHelper()
+    {
+    }
+
+    BigInteger calculatePrivate(DHParameters dhParams, SecureRandom random)
+    {
+        BigInteger p = dhParams.getP();
+        int limit = dhParams.getL();
+
+        if (limit != 0)
+        {
+            return new BigInteger(limit, random).setBit(limit - 1);
+        }
+
+        BigInteger min = TWO;
+        int m = dhParams.getM();
+        if (m != 0)
+        {
+            min = ONE.shiftLeft(m - 1);
+        }
+
+        BigInteger max = p.subtract(TWO);
+        BigInteger q = dhParams.getQ();
+        if (q != null)
+        {
+            max = q.subtract(TWO);
+        }
+
+        return BigIntegers.createRandomInRange(min, max, random);
+    }
+
+    BigInteger calculatePublic(DHParameters dhParams, BigInteger x)
+    {
+        return dhParams.getG().modPow(x, dhParams.getP());
+    }
+}