Crypto: HMAC-SHA256 cleanup

Add byte[] key method to reduce object churn in NTCP2
Un-deprecate in context

core/java/src/net/i2p/I2PAppContext.java

@@ -746,8 +746,9 @@ public class I2PAppContext {
         }
     }
 
-    /** @deprecated used only by syndie */
-    @Deprecated
+    /**
+     * Un-deprecated in 0.9.38
+     */
     public HMAC256Generator hmac256() {
         if (!_hmac256Initialized)
             initializeHMAC256();

core/java/src/net/i2p/crypto/HMAC256Generator.java

@@ -4,6 +4,7 @@ import java.security.GeneralSecurityException;
 import java.security.Key;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import javax.crypto.Mac;
 import javax.crypto.spec.SecretKeySpec;
 
 import net.i2p.I2PAppContext;
@@ -19,7 +20,7 @@ import org.bouncycastle.oldcrypto.macs.I2PHMac;
  *
  * As of 0.9.12, uses javax.crypto.Mac.
  *
- * Deprecated, used only by Syndie.
+ * Warning - used by Syndie, don't break it.
  */
 public final class HMAC256Generator extends HMACGenerator {
 
@@ -33,6 +34,7 @@ public final class HMAC256Generator extends HMACGenerator {
      *  @throws UnsupportedOperationException since 0.9.12
      */
     @Override
+    @Deprecated
     protected I2PHMac acquire() {
         throw new UnsupportedOperationException();
     }
@@ -46,6 +48,7 @@ public final class HMAC256Generator extends HMACGenerator {
      *  @since 0.9.12 overrides HMACGenerator
      */
     @Override
+    @Deprecated
     public Hash calculate(SessionKey key, byte data[]) {
         throw new UnsupportedOperationException();
     }
@@ -60,9 +63,22 @@ public final class HMAC256Generator extends HMACGenerator {
      */
     @Override
     public void calculate(SessionKey key, byte data[], int offset, int length, byte target[], int targetOffset) {
+        calculate(key.getData(), data, offset, length, target, targetOffset);
+    }
+    
+    /**
+     *  Calculate the HMAC of the data with the given key.
+     *  Outputs 32 bytes to target starting at targetOffset.
+     *
+     *  @param key 32 bytes
+     *  @throws UnsupportedOperationException if the JVM does not support it
+     *  @throws IllegalArgumentException for bad key or target too small
+     *  @since 0.9.38
+     */
+    public void calculate(byte[] key, byte data[], int offset, int length, byte target[], int targetOffset) {
         try {
-            javax.crypto.Mac mac = javax.crypto.Mac.getInstance("HmacSHA256");
-            Key keyObj = new SecretKeySpec(key.getData(), "HmacSHA256");
+            Mac mac = Mac.getInstance("HmacSHA256");
+            Key keyObj = new SecretKeySpec(key, "HmacSHA256");
             mac.init(keyObj);
             mac.update(data, offset, length);
             mac.doFinal(target, targetOffset);

router/java/src/net/i2p/router/transport/ntcp/OutboundNTCP2State.java

@@ -436,34 +436,28 @@ class OutboundNTCP2State implements EstablishState {
     static byte[][] generateSipHashKeys(RouterContext ctx, HandshakeState state) {
         // TODO use noise HMAC or HKDF method instead?
         // ask_master = HKDF(ck, zerolen, info="ask")
-        SessionKey tk = new SessionKey(state.getChainingKey());
-        byte[] temp_key = doHMAC(ctx, tk, ZEROLEN);
-        tk = new SessionKey(temp_key);
-        byte[] ask_master = doHMAC(ctx, tk, ASK);
+        byte[] temp_key = doHMAC(ctx, state.getChainingKey(), ZEROLEN);
+        byte[] ask_master = doHMAC(ctx, temp_key, ASK);
         byte[] tmp = new byte[32 + SIPHASH.length];
         byte[] hash = state.getHandshakeHash();
         System.arraycopy(hash, 0, tmp, 0, 32);
         System.arraycopy(SIPHASH, 0, tmp, 32, SIPHASH.length); 
-        tk = new SessionKey(ask_master);
-        temp_key = doHMAC(ctx, tk, tmp);
-        tk = new SessionKey(temp_key);
-        byte[] sip_master = doHMAC(ctx, tk, ONE);
-        tk = new SessionKey(sip_master);
-        temp_key = doHMAC(ctx, tk, ZEROLEN);
-        tk = new SessionKey(temp_key);
+        temp_key = doHMAC(ctx, ask_master, tmp);
+        byte[] sip_master = doHMAC(ctx, temp_key, ONE);
+        temp_key = doHMAC(ctx, sip_master, ZEROLEN);
         // Output 1
-        byte[] sip_ab = doHMAC(ctx, tk, ONE);
+        byte[] sip_ab = doHMAC(ctx, temp_key, ONE);
         // Output 2
         tmp = new byte[KEY_SIZE + 1];
         System.arraycopy(sip_ab, 0, tmp, 0, 32);
         tmp[32] = 2;
-        byte[] sip_ba = doHMAC(ctx, tk, tmp);
+        byte[] sip_ba = doHMAC(ctx, temp_key, tmp);
         Arrays.fill(temp_key, (byte) 0);
         Arrays.fill(tmp, (byte) 0);
         return new byte[][] { sip_ab, sip_ba };
     }
 
-    private static byte[] doHMAC(RouterContext ctx, SessionKey key, byte data[]) {
+    private static byte[] doHMAC(RouterContext ctx, byte[] key, byte[] data) {
         byte[] rv = new byte[32];
         ctx.hmac256().calculate(key, data, 0, data.length, rv, 0);
         return rv;