diff --git a/android/project/jni/fwknop/fwknop_client.c b/android/project/jni/fwknop/fwknop_client.c
index 19adba56..ed835dad 100644
--- a/android/project/jni/fwknop/fwknop_client.c
+++ b/android/project/jni/fwknop/fwknop_client.c
@@ -45,7 +45,7 @@ jstring Java_com_max2idea_android_fwknop_Fwknop_sendSPAPacket(JNIEnv* env,
     fko_ctx_t ctx;
     fwknop_options_t opts;
 
-    int res;
+    int res, hmac_str_len = 0;
     char res_msg[MSG_BUFSIZE+1] = {0};
     char spa_msg[MSG_BUFSIZE+1] = {0};
 
@@ -72,6 +72,10 @@ jstring Java_com_max2idea_android_fwknop_Fwknop_sendSPAPacket(JNIEnv* env,
     jstring jpasswd = (*env)->GetObjectField(env, thiz, fid);
     const char *passwd_str = (*env)->GetStringUTFChars(env, jpasswd, 0);
 
+    fid = (*env)->GetFieldID(env, c, "hmac_str", "Ljava/lang/String;");
+    jstring jhmac = (*env)->GetObjectField(env, thiz, fid);
+    const char *hmac_str = (*env)->GetStringUTFChars(env, jhmac, 0);
+
     fid = (*env)->GetFieldID(env, c, "fw_timeout_str", "Ljava/lang/String;");
     jstring jfwtimeout = (*env)->GetObjectField(env, thiz, fid);
     const char *fw_timeout_str = (*env)->GetStringUTFChars(env, jfwtimeout, 0);
@@ -99,6 +103,12 @@ jstring Java_com_max2idea_android_fwknop_Fwknop_sendSPAPacket(JNIEnv* env,
         goto cleanup2;
     }
 
+    /* Using an HMAC is optional (currently)
+    */
+    if(hmac_str != NULL) {
+        hmac_str_len = (int)strlen(hmac_str);
+    }
+
     /* Set our spa server info
     */
     opts.spa_server_str = (char*)destip_str;
@@ -130,9 +140,20 @@ jstring Java_com_max2idea_android_fwknop_Fwknop_sendSPAPacket(JNIEnv* env,
         goto cleanup;
     }
 
+    /* Set the HMAC mode if necessary
+    */
+    if (hmac_str_len > 0) {
+        res = fko_set_spa_hmac_type(ctx, FKO_DEFAULT_HMAC_MODE);
+        if (res != FKO_SUCCESS) {
+            strcpy(res_msg, fko_errmsg("Error setting SPA HMAC type", res));
+            goto cleanup;
+        }
+    }
+
     /* Finalize the context data (Encrypt and encode).
     */
-    res = fko_spa_data_final(ctx, (char*)passwd_str);
+    res = fko_spa_data_final(ctx, (char*)passwd_str,
+            (int)strlen(passwd_str), (char *)hmac_str, hmac_str_len);
     if (res != FKO_SUCCESS) {
         strcpy(res_msg, fko_errmsg("Error generating SPA data", res));
         goto cleanup;
@@ -173,6 +194,7 @@ cleanup2:
     (*env)->ReleaseStringUTFChars(env, jallowip, allowip_str);
     (*env)->ReleaseStringUTFChars(env, jdestip, destip_str);
     (*env)->ReleaseStringUTFChars(env, jpasswd, passwd_str);
+    (*env)->ReleaseStringUTFChars(env, jhmac, hmac_str);
     (*env)->ReleaseStringUTFChars(env, jfwtimeout, fw_timeout_str);
 
     /* Log and return a string of success or error message.
diff --git a/android/project/res/layout/main.xml b/android/project/res/layout/main.xml
index e98a0efc..e53650a0 100644
--- a/android/project/res/layout/main.xml
+++ b/android/project/res/layout/main.xml
@@ -133,6 +133,28 @@
             android:textSize="20dip"
             />
     </LinearLayout>
+    <LinearLayout android:id="@+id/hmacl"
+                  android:orientation="horizontal"
+                  android:layout_width="fill_parent"
+                  android:layout_height="wrap_content"
+                  >
+        <TextView
+            android:id="@+id/hmacStr"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="HMAC Key: "
+            android:textSize="20dip"
+            />
+        <EditText
+            android:id="@+id/hmac"
+            android:layout_width="fill_parent"
+            android:layout_height="wrap_content"
+            android:text=""
+            android:singleLine="true"
+            android:password="true"
+            android:textSize="20dip"
+            />
+    </LinearLayout>
     <RelativeLayout android:id="@+id/startAppl"
                     android:orientation="horizontal"
                     android:layout_width="fill_parent"
diff --git a/android/project/src/com/max2idea/android/fwknop/Fwknop.java b/android/project/src/com/max2idea/android/fwknop/Fwknop.java
index bf3bf9b2..ee8ce31b 100644
--- a/android/project/src/com/max2idea/android/fwknop/Fwknop.java
+++ b/android/project/src/com/max2idea/android/fwknop/Fwknop.java
@@ -94,6 +94,7 @@ public class Fwknop extends Activity {
     private String output;
     private Spinner mAllowip;
     private EditText mPasswd;
+    private EditText mHmac;
     private EditText mDestip;
     private Spinner mAccessProto;
     private EditText mAccessPort;
@@ -102,6 +103,7 @@ public class Fwknop extends Activity {
     private String access_str;
     private String allowip_str;
     private String passwd_str;
+    private String hmac_str;
     private String destip_str;
     private String fw_timeout_str;
     private CheckBox mCheck;
@@ -303,6 +305,15 @@ public class Fwknop extends Activity {
             return;
         }
 
+        if (this.mHmac != null && !this.mHmac.getText().toString().trim().equals("")) {
+            this.hmac_str = mHmac.getText().toString();
+            edit.putString("hmac_str", mHmac.getText().toString());
+        } else {
+            // the HMAC is currently optional
+            this.hmac_str = "";
+            edit.putString("hmac_str", this.hmac_str);
+        }
+
         if (this.mDestip != null && !this.mDestip.getText().toString().trim().equals("")) {
             this.destip_str = mDestip.getText().toString();
             edit.putString("destip_str", mDestip.getText().toString());
@@ -367,6 +378,8 @@ public class Fwknop extends Activity {
         this.mPasswd = (EditText) findViewById(R.id.passwd);
         this.mOutput = (TextView) findViewById(R.id.output);
 
+        this.mHmac   = (EditText) findViewById(R.id.hmac);
+
         mUnlock = (ImageButton) findViewById(R.id.unlock);
         mUnlock.setOnClickListener(new OnClickListener() {