1 files changed, 24 insertions, 0 deletions
diff --git a/source/storage/KeyManager.mc b/source/storage/KeyManager.mc
index 567288f..47dbd59 100644
--- a/source/storage/KeyManager.mc
+++ b/source/storage/KeyManager.mc
@@ -84,6 +84,30 @@ class KeyManager {
         return out;
     }
 
+    // A keyed hash (16 hex characters) of a settings form's content, for
+    // the applied-forms log (README 10.3). Keyed like the fingerprints, with
+    // its own label, because the content includes secrets. The parts are
+    // fed to the native HMAC one by one, each preceded by `separator`, so a
+    // large import form costs no byte loop here (the watchdog).
+    function formHash(parts as Array<ByteArray>, separator as Number) as String {
+        deviceKeys();
+        var mac = new Cryptography.HashBasedMessageAuthenticationCode({
+            :algorithm => Cryptography.HASH_SHA256,
+            :key => _fingerprintKey as ByteArray
+        });
+        mac.update(Bytes.fromUtf8("OTPW-FH-1"));
+        for (var i = 0; i < parts.size(); i++) {
+            mac.update([separator]b);
+            if (parts[i].size() > 0) {
+                mac.update(parts[i]);
+            }
+        }
+        var digest = mac.digest();
+        var out = Bytes.toHex(digest.slice(0, FINGERPRINT_BYTES));
+        Bytes.wipe(digest);
+        return out;
+    }
+
     // True when a PIN has been set.
     function hasPin() as Boolean {
         return _store.getValue(WRAP_KEY) != null;