From ac4ab7b08e58e22a1126f3217cf812926929bc79 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Fri, 24 Jun 2022 19:02:13 +0000
Subject: SyntheticPasswordManager: consolidate hex encoding logic

Remove the in-class implementation of hex encoding and just use
HexEncoding, which was already being used in one place.

No change in behavior since the encoding remains the same.  In
particular, upper case A-F is still used instead of lower case a-f.

Test: atest SyntheticPasswordTests
Change-Id: I493e4b894f76670bcb9cba8a8a774f3f5832e769
---
 .../locksettings/SyntheticPasswordManager.java       | 20 +++++---------------
 .../server/locksettings/SyntheticPasswordTests.java  |  7 +++++++
 2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/services/core/java/com/android/server/locksettings/SyntheticPasswordManager.java b/services/core/java/com/android/server/locksettings/SyntheticPasswordManager.java
index 111ffd29228c..5fdfe1983f0a 100644
--- a/services/core/java/com/android/server/locksettings/SyntheticPasswordManager.java
+++ b/services/core/java/com/android/server/locksettings/SyntheticPasswordManager.java
@@ -272,9 +272,8 @@ public class SyntheticPasswordManager {
          * AuthenticationToken.mSyntheticPassword for details on what each block means.
          */
         private void recreate(byte[] escrowSplit0, byte[] escrowSplit1) {
-            mSyntheticPassword = String.valueOf(HexEncoding.encode(
-                    SyntheticPasswordCrypto.personalisedHash(
-                            PERSONALIZATION_SP_SPLIT, escrowSplit0, escrowSplit1))).getBytes();
+            mSyntheticPassword = bytesToHex(SyntheticPasswordCrypto.personalisedHash(
+                    PERSONALIZATION_SP_SPLIT, escrowSplit0, escrowSplit1));
         }
 
         /**
@@ -1415,18 +1414,9 @@ public class SyntheticPasswordManager {
         return result;
     }
 
-    protected static final byte[] HEX_ARRAY = "0123456789ABCDEF".getBytes();
-    private static byte[] bytesToHex(byte[] bytes) {
-        if (bytes == null) {
-            return "null".getBytes();
-        }
-        byte[] hexBytes = new byte[bytes.length * 2];
-        for ( int j = 0; j < bytes.length; j++ ) {
-            int v = bytes[j] & 0xFF;
-            hexBytes[j * 2] = HEX_ARRAY[v >>> 4];
-            hexBytes[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
-        }
-        return hexBytes;
+    @VisibleForTesting
+    static byte[] bytesToHex(byte[] bytes) {
+        return HexEncoding.encodeToString(bytes).getBytes();
     }
 
     /**
diff --git a/services/tests/servicestests/src/com/android/server/locksettings/SyntheticPasswordTests.java b/services/tests/servicestests/src/com/android/server/locksettings/SyntheticPasswordTests.java
index c0a38b874914..b5eea70f57a4 100644
--- a/services/tests/servicestests/src/com/android/server/locksettings/SyntheticPasswordTests.java
+++ b/services/tests/servicestests/src/com/android/server/locksettings/SyntheticPasswordTests.java
@@ -567,6 +567,13 @@ public class SyntheticPasswordTests extends BaseLockSettingsServiceTests {
         }
     }
 
+    @Test
+    public void testHexEncodingIsUppercase() {
+        final byte[] raw = new byte[] { (byte)0xAB, (byte)0xCD, (byte)0xEF };
+        final byte[] expected = new byte[] { 'A', 'B', 'C', 'D', 'E', 'F' };
+        assertArrayEquals(expected, SyntheticPasswordManager.bytesToHex(raw));
+    }
+
     // b/62213311
     //TODO: add non-migration work profile case, and unify/un-unify transition.
     //TODO: test token after user resets password
-- 
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