1 files changed, 63 insertions, 0 deletions
diff --git a/bcprov/src/main/java/org/bouncycastle/crypto/generators/CramerShoupKeyPairGenerator.java b/bcprov/src/main/java/org/bouncycastle/crypto/generators/CramerShoupKeyPairGenerator.java
new file mode 100644
index 0000000..8fcdf85
--- /dev/null
+++ b/bcprov/src/main/java/org/bouncycastle/crypto/generators/CramerShoupKeyPairGenerator.java
@@ -0,0 +1,63 @@
+package org.bouncycastle.crypto.generators;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
+
+import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
+import org.bouncycastle.crypto.AsymmetricCipherKeyPairGenerator;
+import org.bouncycastle.crypto.KeyGenerationParameters;
+import org.bouncycastle.crypto.params.CramerShoupKeyGenerationParameters;
+import org.bouncycastle.crypto.params.CramerShoupParameters;
+import org.bouncycastle.crypto.params.CramerShoupPrivateKeyParameters;
+import org.bouncycastle.crypto.params.CramerShoupPublicKeyParameters;
+import org.bouncycastle.util.BigIntegers;
+
+/**
+ * a Cramer Shoup key pair generator
+ * 
+ */
+public class CramerShoupKeyPairGenerator implements AsymmetricCipherKeyPairGenerator {
+	
+	private static final BigInteger ONE = BigInteger.valueOf(1);
+
+	private CramerShoupKeyGenerationParameters param;
+
+	public void init(KeyGenerationParameters param) {
+		this.param = (CramerShoupKeyGenerationParameters) param;
+	}
+
+	public AsymmetricCipherKeyPair generateKeyPair() {
+		CramerShoupParameters csParams = param.getParameters();
+
+		CramerShoupPrivateKeyParameters sk = generatePrivateKey(param.getRandom(), csParams);
+		CramerShoupPublicKeyParameters pk = calculatePublicKey(csParams, sk);
+		sk.setPk(pk);
+
+		return new AsymmetricCipherKeyPair(pk, sk);
+	}
+
+	private BigInteger generateRandomElement(BigInteger p, SecureRandom random) {
+		return BigIntegers.createRandomInRange(ONE, p.subtract(ONE), random);
+	}
+	
+	private CramerShoupPrivateKeyParameters generatePrivateKey(SecureRandom random, CramerShoupParameters csParams){
+		BigInteger p = csParams.getP();
+		CramerShoupPrivateKeyParameters key = new CramerShoupPrivateKeyParameters(csParams,
+				generateRandomElement(p, random), generateRandomElement(p, random),
+				generateRandomElement(p, random), generateRandomElement(p, random),
+				generateRandomElement(p, random));
+		return key;
+	}
+
+	private CramerShoupPublicKeyParameters calculatePublicKey(CramerShoupParameters csParams, CramerShoupPrivateKeyParameters sk) {
+		BigInteger g1 = csParams.getG1();
+		BigInteger g2 = csParams.getG2();
+		BigInteger p = csParams.getP();
+		
+		BigInteger c = g1.modPow(sk.getX1(), p).multiply(g2.modPow(sk.getX2(), p));
+		BigInteger d = g1.modPow(sk.getY1(), p).multiply(g2.modPow(sk.getY2(), p));
+		BigInteger h = g1.modPow(sk.getZ(), p);
+		
+		return new CramerShoupPublicKeyParameters(csParams, c, d, h);
+	}
+}