Avoid redundant engine creation

Author: peterdettman

core/src/main/java/org/bouncycastle/pqc/crypto/slhdsa/SLHDSAKeyPairGenerator.java

@@ -20,30 +20,32 @@ public void init(KeyGenerationParameters param)
 
     public AsymmetricCipherKeyPair internalGenerateKeyPair(byte[] skSeed, byte[] skPrf, byte[] pkSeed)
     {
-        SLHDSAEngine engine = parameters.getEngine();
-        SK sk = new SK(skSeed, skPrf);
+        return implGenerateKeyPair(parameters.getEngine(), skSeed, skPrf, pkSeed);
+    }
 
-        engine.init(pkSeed);
+    public AsymmetricCipherKeyPair generateKeyPair()
+    {
+        SLHDSAEngine engine = parameters.getEngine();
 
-        // TODO
-        PK pk = new PK(pkSeed, new HT(engine, sk.seed, pkSeed).htPubKey);
+        byte[] skSeed = sec_rand(engine.N);
+        byte[] skPrf = sec_rand(engine.N);
+        byte[] pkSeed = sec_rand(engine.N);
 
-        return new AsymmetricCipherKeyPair(new SLHDSAPublicKeyParameters(parameters, pk),
-                new SLHDSAPrivateKeyParameters(parameters, sk, pk));
+        return implGenerateKeyPair(engine, skSeed, skPrf, pkSeed);
     }
 
-    public AsymmetricCipherKeyPair generateKeyPair()
+    private AsymmetricCipherKeyPair implGenerateKeyPair(SLHDSAEngine engine, byte[] skSeed, byte[] skPrf, byte[] pkSeed)
     {
-        SLHDSAEngine engine = parameters.getEngine();
-        byte[] pkSeed;
-        byte[] skSeed;
-        byte[] skPrf;
+        SK sk = new SK(skSeed, skPrf);
 
+        engine.init(pkSeed);
+
+        // TODO
+        PK pk = new PK(pkSeed, new HT(engine, sk.seed, pkSeed).htPubKey);
 
-        skSeed = sec_rand(engine.N);
-        skPrf = sec_rand(engine.N);
-        pkSeed = sec_rand(engine.N);
-        return internalGenerateKeyPair(skSeed, skPrf, pkSeed);
+        return new AsymmetricCipherKeyPair(
+            new SLHDSAPublicKeyParameters(parameters, pk),
+            new SLHDSAPrivateKeyParameters(parameters, sk, pk));
     }
 
     private byte[] sec_rand(int n)