feat(crypto): add SHA-512, HMAC, PBKDF2, HKDF, AES-256 records and self-test

- Sha512: FIPS 180-4 in Monkey C (no native SHA-512), rotations inlined
  with precomputed masks; constants derived from the primes, not typed.
- Hmac: RFC 2104 over SHA-1/256/512 (native HMAC only supports SHA-256).
- Kdf: resumable PBKDF2-HMAC-SHA256 job with calibration bounds
  (2,000-200,000 iterations) and HKDF-SHA256.
- Aes: CBC with PKCS#7 over the native cipher; AES-256 chosen.
- SealedBox: encrypt-then-MAC records (HKDF-split keys, length-prefixed
  aad, constant-time tag check before decryption).
- SelfTest: known-answer tests for every primitive at start-up.
- Bytes (wipe, constant-time equal), Clock (2038-safe widening, trusted
  clock), Jobs (bounded steps against the watchdog, timer runner).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/source/util/Clock.mc b/source/util/Clock.mc
new file mode 100644
index 0000000..4e2faf4
--- /dev/null
+++ b/source/util/Clock.mc
@@ -0,0 +1,36 @@
+// Author:  cirakg & claude ai
+// Summary: UTC time for TOTP: the 2038-safe widening of the watch clock, the user's offset, and the trusted clock.
+//
+// Connect IQ stores time as a 32-bit signed integer, which turns negative on
+// 2038-01-19. Reading it as unsigned keeps it correct until 2106 (README 9).
+// The trusted clock (Time.CURRENT_TIME_RTC, API 3.0.10) is synced from GPS and
+// can't be changed by the user; the UI warns when it is unsynced or differs
+// from the normal clock.
+
+import Toybox.Lang;
+import Toybox.Time;
+
+module Clock {
+
+    const TWO_POW_32 = 4294967296l;
+
+    // A 32-bit clock value read as unsigned.
+    function toUnsigned(value as Number) as Long {
+        var v = value.toLong();
+        return v < 0 ? v + TWO_POW_32 : v;
+    }
+
+    // Current unix time (UTC seconds) plus the user's offset for clock skew.
+    function nowUnix(offsetSeconds as Number) as Long {
+        return toUnsigned(Time.now().value()) + offsetSeconds;
+    }
+
+    // The trusted clock's unix time, or null when it isn't synced yet.
+    function trustedUnix() as Long? {
+        try {
+            return toUnsigned(Time.getCurrentTime({:currentTimeType => Time.CURRENT_TIME_RTC}).value());
+        } catch (e instanceof Time.RealTimeClockNotValidException) {
+            return null;
+        }
+    }
+}