1 files changed, 66 insertions, 11 deletions
diff --git a/src/java/com/android/ike/ikev2/message/IkeAuthPskPayload.java b/src/java/com/android/ike/ikev2/message/IkeAuthPskPayload.java
index 63f45dd5..213e24a3 100644
--- a/src/java/com/android/ike/ikev2/message/IkeAuthPskPayload.java
+++ b/src/java/com/android/ike/ikev2/message/IkeAuthPskPayload.java
@@ -16,9 +16,10 @@
 
 package com.android.ike.ikev2.message;
 
-import com.android.ike.ikev2.exceptions.IkeException;
-
 import java.nio.ByteBuffer;
+import java.security.InvalidKeyException;
+
+import javax.crypto.Mac;
 
 /**
  * IkeAuthPskPayload represents an Authentication Payload using Pre-Shared Key to do authentication.
@@ -27,25 +28,79 @@ import java.nio.ByteBuffer;
  *     Protocol Version 2 (IKEv2).
  */
 public final class IkeAuthPskPayload extends IkeAuthPayload {
+    // Hex of ASCII characters "Key Pad for IKEv2" for calculating PSK signature.
+    private static final byte[] IKE_KEY_PAD_STRING_ASCII_HEX_BYTES = {
+        (byte) 0x4b, (byte) 0x65, (byte) 0x79, (byte) 0x20,
+        (byte) 0x50, (byte) 0x61, (byte) 0x64, (byte) 0x20,
+        (byte) 0x66, (byte) 0x6f, (byte) 0x72, (byte) 0x20,
+        (byte) 0x49, (byte) 0x4b, (byte) 0x45, (byte) 0x76,
+        (byte) 0x32
+    };
+
     public final byte[] signature;
 
-    protected IkeAuthPskPayload(boolean critical, byte[] authData) throws IkeException {
+    /**
+     * Construct IkeAuthPskPayload for received IKE packet in the context of {@link
+     * IkePayloadFactory}.
+     */
+    protected IkeAuthPskPayload(boolean critical, byte[] authData) {
         super(critical, IkeAuthPayload.AUTH_METHOD_PRE_SHARED_KEY);
         signature = authData;
     }
 
+    /**
+     * Construct IkeAuthPskPayload for an outbound IKE packet.
+     *
+     * <p>Since IKE library is always a client, outbound IkeAuthPskPayload always signs IKE
+     * initiator's SignedOctets, which is concatenation of the IKE_INIT request message, the Nonce
+     * of IKE responder and the signed ID-Initiator payload body.
+     *
+     * @param psk locally stored pre-shared key
+     * @param ikeInitBytes IKE_INIT request for calculating IKE initiator's SignedOctets.
+     * @param nonce nonce of IKE responder for calculating IKE initiator's SignedOctets.
+     * @param idPayloadBodyBytes ID-Initiator payload body for calculating IKE initiator's
+     *     SignedOctets.
+     * @param prfMac locally store PRF
+     * @param prfKeyBytes locally store PRF keys
+     */
+    public IkeAuthPskPayload(
+            byte[] psk,
+            byte[] ikeInitBytes,
+            byte[] nonce,
+            byte[] idPayloadBodyBytes,
+            Mac prfMac,
+            byte[] prfKeyBytes) {
+        super(false, IkeAuthPayload.AUTH_METHOD_PRE_SHARED_KEY);
+        signature =
+                calculatePskSignature(
+                        psk, ikeInitBytes, nonce, idPayloadBodyBytes, prfMac, prfKeyBytes);
+    }
+
+    private static byte[] calculatePskSignature(
+            byte[] psk,
+            byte[] ikeInitBytes,
+            byte[] nonce,
+            byte[] idPayloadBodyBytes,
+            Mac prfMac,
+            byte[] prfKeyBytes) {
+        try {
+            byte[] signingKeyBytes = signWithPrf(prfMac, psk, IKE_KEY_PAD_STRING_ASCII_HEX_BYTES);
+            byte[] dataToSignBytes =
+                    getSignedOctets(ikeInitBytes, nonce, idPayloadBodyBytes, prfMac, prfKeyBytes);
+            return signWithPrf(prfMac, signingKeyBytes, dataToSignBytes);
+        } catch (InvalidKeyException e) {
+            throw new IllegalArgumentException("Locally stored PRF key is invalid: ", e);
+        }
+    }
+
     @Override
-    protected void encodeToByteBuffer(@PayloadType int nextPayload, ByteBuffer byteBuffer) {
-        // TODO: Implement it.
-        throw new UnsupportedOperationException(
-                "It is not supported to encode a " + getTypeString());
+    protected void encodeAuthDataToByteBuffer(ByteBuffer byteBuffer) {
+        byteBuffer.put(signature);
     }
 
     @Override
-    protected int getPayloadLength() {
-        // TODO: Implement it.
-        throw new UnsupportedOperationException(
-                "It is not supported to get payload length of " + getTypeString());
+    protected int getAuthDataLength() {
+        return signature.length;
     }
 
     @Override