Add option to use a custom attestation challenge

When generating a private/public key pair a text box now appears
asking for a custom challenge (in Base64) under the checkbox
"Include key attestation challenge". The default challenge is 'abc'
('YWJj' in Base64).

Bug: 159901371
Change-Id: I0b275205eb53f92cd58792892d861a3666947b0a

Author: Elis Elliott

app/src/main/java/com/afwsamples/testdpc/policy/PolicyManagementFragment.java

@@ -64,6 +64,7 @@
 import android.telephony.TelephonyManager;
 import android.text.InputType;
 import android.text.TextUtils;
+import android.util.Base64;
 import android.util.Log;
 import android.util.SparseIntArray;
 import android.view.LayoutInflater;
@@ -2777,6 +2778,10 @@ private void showPromptForGeneratedKeyAlias(String alias) {
                 R.id.use_individual_attestation);
         useIndividualAttestationCheckbox.setEnabled(Util.SDK_INT >= VERSION_CODES.R);
 
+        // Custom Challenge input
+        final EditText customChallengeInput = aliasNamingView.findViewById(
+                R.id.custom_challenge_input);
+
         new AlertDialog.Builder(getActivity())
                 .setTitle(getString(R.string.certificate_alias_prompt_title))
                 .setView(aliasNamingView)
@@ -2789,7 +2794,11 @@ public void onClick(DialogInterface dialog, int which) {
                         paramsBuilder.setIsUserSelectable(userSelectableCheckbox.isChecked());
 
                         if (includeAttestationChallengeCheckbox.isChecked()) {
-                            paramsBuilder.setAttestationChallenge(new byte[] {0x61, 0x62, 0x63});
+                            String customChallenge = customChallengeInput.getText().toString()
+                                .trim();
+                            byte[] decodedChallenge = Base64.decode(customChallenge,
+                                Base64.DEFAULT);
+                            paramsBuilder.setAttestationChallenge(decodedChallenge);
                         }
 
                         int idAttestationFlags = 0;

app/src/main/res/layout/key_generation_prompt.xml

@@ -64,6 +64,18 @@
         android:layout_height="wrap_content"
         android:text="@string/key_attestation_checkbox"/>
 
+    <EditText
+        android:id="@+id/custom_challenge_input"
+        android:layout_width="fill_parent"
+        android:layout_height="wrap_content"
+        android:lines="1"
+        android:maxLines="1"
+        android:scrollHorizontally="true"
+        android:ellipsize="end"
+        android:inputType="text"
+        android:text="YWJj"
+        android:hint="Custom Challenge (Base64)"/>
+
     <TextView
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"