1 files changed, 105 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/tls/TlsDHUtils.java b/core/src/main/java/org/spongycastle/crypto/tls/TlsDHUtils.java
new file mode 100644
index 00000000..9a7a2218
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/tls/TlsDHUtils.java
@@ -0,0 +1,105 @@
+package org.spongycastle.crypto.tls;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.spongycastle.crypto.AsymmetricCipherKeyPair;
+import org.spongycastle.crypto.agreement.DHBasicAgreement;
+import org.spongycastle.crypto.generators.DHBasicKeyPairGenerator;
+import org.spongycastle.crypto.params.DHKeyGenerationParameters;
+import org.spongycastle.crypto.params.DHParameters;
+import org.spongycastle.crypto.params.DHPrivateKeyParameters;
+import org.spongycastle.crypto.params.DHPublicKeyParameters;
+import org.spongycastle.util.BigIntegers;
+
+public class TlsDHUtils
+{
+    static final BigInteger ONE = BigInteger.valueOf(1);
+    static final BigInteger TWO = BigInteger.valueOf(2);
+
+    public static boolean areCompatibleParameters(DHParameters a, DHParameters b)
+    {
+        return a.getP().equals(b.getP()) && a.getG().equals(b.getG());
+    }
+
+    public static byte[] calculateDHBasicAgreement(DHPublicKeyParameters publicKey, DHPrivateKeyParameters privateKey)
+    {
+        DHBasicAgreement basicAgreement = new DHBasicAgreement();
+        basicAgreement.init(privateKey);
+        BigInteger agreementValue = basicAgreement.calculateAgreement(publicKey);
+
+        /*
+         * RFC 5246 8.1.2. Leading bytes of Z that contain all zero bits are stripped before it is
+         * used as the pre_master_secret.
+         */
+        return BigIntegers.asUnsignedByteArray(agreementValue);
+    }
+
+    public static AsymmetricCipherKeyPair generateDHKeyPair(SecureRandom random, DHParameters dhParams)
+    {
+        DHBasicKeyPairGenerator dhGen = new DHBasicKeyPairGenerator();
+        dhGen.init(new DHKeyGenerationParameters(random, dhParams));
+        return dhGen.generateKeyPair();
+    }
+
+    public static DHPrivateKeyParameters generateEphemeralClientKeyExchange(SecureRandom random, DHParameters dhParams,
+        OutputStream output) throws IOException
+    {
+        AsymmetricCipherKeyPair kp = generateDHKeyPair(random, dhParams);
+
+        DHPublicKeyParameters dh_public = (DHPublicKeyParameters) kp.getPublic();
+        writeDHParameter(dh_public.getY(), output);
+
+        return (DHPrivateKeyParameters) kp.getPrivate();
+    }
+
+    public static DHPrivateKeyParameters generateEphemeralServerKeyExchange(SecureRandom random, DHParameters dhParams,
+        OutputStream output) throws IOException
+    {
+        AsymmetricCipherKeyPair kp = TlsDHUtils.generateDHKeyPair(random, dhParams);
+
+        DHPublicKeyParameters dhPublicKey = (DHPublicKeyParameters)kp.getPublic();
+        ServerDHParams params = new ServerDHParams(dhPublicKey);
+        params.encode(output);
+
+        return (DHPrivateKeyParameters)kp.getPrivate();
+    }
+
+    public static DHPublicKeyParameters validateDHPublicKey(DHPublicKeyParameters key) throws IOException
+    {
+        BigInteger Y = key.getY();
+        DHParameters params = key.getParameters();
+        BigInteger p = params.getP();
+        BigInteger g = params.getG();
+
+        if (!p.isProbablePrime(2))
+        {
+            throw new TlsFatalAlert(AlertDescription.illegal_parameter);
+        }
+        if (g.compareTo(TWO) < 0 || g.compareTo(p.subtract(TWO)) > 0)
+        {
+            throw new TlsFatalAlert(AlertDescription.illegal_parameter);
+        }
+        if (Y.compareTo(TWO) < 0 || Y.compareTo(p.subtract(ONE)) > 0)
+        {
+            throw new TlsFatalAlert(AlertDescription.illegal_parameter);
+        }
+
+        // TODO See RFC 2631 for more discussion of Diffie-Hellman validation
+
+        return key;
+    }
+
+    public static BigInteger readDHParameter(InputStream input) throws IOException
+    {
+        return new BigInteger(1, TlsUtils.readOpaque16(input));
+    }
+
+    public static void writeDHParameter(BigInteger x, OutputStream output) throws IOException
+    {
+        TlsUtils.writeOpaque16(BigIntegers.asUnsignedByteArray(x), output);
+    }
+}