ussl: Add support for sign callback on MicroPython.

Signed-off-by: iabdalkader <[email protected]>

Author: iabdalkader

src/arduino_iot_cloud/ussl.py

@@ -9,22 +9,56 @@
 import ssl
 import sys
 import logging
-import binascii
+try:
+    from micropython import const
+except (ImportError, AttributeError):
+    def const(x):
+        return x
 
 pkcs11 = None
+se_dev = None
 
 # Default engine and provider.
 _ENGINE_PATH = "/usr/lib/engines-3/libpkcs11.so"
 _MODULE_PATH = "/usr/lib/softhsm/libsofthsm2.so"
 
-# Reference EC key for NXP's PlugNTrust
-_EC_REF_KEY = binascii.unhexlify(
-    b"3041020100301306072a8648ce3d020106082a8648ce3d03010704273025"
-    b"0201010420100000000000000000000000000000000000ffffffffa5a6b5"
-    b"b6a5a6b5b61000"
+# Reference EC key for the SE.
+_EC_REF_KEY = const(
+    b"\x30\x41\x02\x01\x00\x30\x13\x06\x07\x2A\x86\x48\xCE\x3D\x02\x01"
+    b"\x06\x08\x2A\x86\x48\xCE\x3D\x03\x01\x07\x04\x27\x30\x25\x02\x01"
+    b"\x01\x04\x20\xA5\xA6\xB5\xB6\xA5\xA6\xB5\xB6\x00\x00\x00\x00\x00"
+    b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xFF"
+    b"\xFF\xFF\xFF"
 )
 
 
+def log_level_enabled(level):
+    return logging.getLogger().isEnabledFor(level)
+
+
+def ecdsa_sign_callback(key, data):
+    if log_level_enabled(logging.DEBUG):
+        key_hex = "".join("%02X" % b for b in key)
+        logging.debug(f"ecdsa_sign_callback key:{key_hex}")
+
+    if key[0:8] != b"\xA5\xA6\xB5\xB6\xA5\xA6\xB5\xB6":
+        if log_level_enabled(logging.DEBUG):
+            logging.debug("ecdsa_sign_callback falling back to default sign")
+        return None
+
+    obj_id = int.from_bytes(key[-4:], "big")
+    if log_level_enabled(logging.DEBUG):
+        logging.debug(f"ecdsa_sign_callback oid: 0x{obj_id:02X}")
+
+    # Sign data on SE using reference key object id.
+    sig = se_dev.sign(obj_id, data)
+    if log_level_enabled(logging.DEBUG):
+        sig_hex = "".join("%02X" % b for b in sig)
+        logging.debug(f"ecdsa_sign_callback sig: {sig_hex}")
+    logging.info("Signed using secure element")
+    return sig
+
+
 def wrap_socket(sock, ssl_params={}):
     keyfile = ssl_params.get("keyfile", None)
     certfile = ssl_params.get("certfile", None)
@@ -33,16 +67,27 @@ def wrap_socket(sock, ssl_params={}):
     ciphers = ssl_params.get("ciphers", None)
     verify = ssl_params.get("verify_mode", ssl.CERT_NONE)
     hostname = ssl_params.get("server_hostname", None)
-    micropython = sys.implementation.name == "micropython"
 
-    if keyfile is not None and "token" in keyfile and micropython:
-        # Create a reference EC key for NXP EdgeLock device.
-        objid = int(keyfile.split("=")[1], 16).to_bytes(4, "big")
-        keyfile = _EC_REF_KEY[0:53] + objid + _EC_REF_KEY[57:]
-        # Load the certificate from the secure element (when supported).
-        # import cryptoki
-        # with cryptoki.open() as token:
-        #     cert = token.read(0x65, 412)
+    se_key_token = keyfile is not None and "token" in keyfile
+    se_crt_token = certfile is not None and "token" in certfile
+    sys_micropython = sys.implementation.name == "micropython"
+
+    if sys_micropython and (se_key_token or se_crt_token):
+        import se05x
+
+        # Create and initialize SE05x device.
+        global se_dev
+        if se_dev is None:
+            se_dev = se05x.SE05X()
+
+        if se_key_token:
+            # Create a reference key for the secure element.
+            obj_id = int(keyfile.split("=")[1], 16)
+            keyfile = _EC_REF_KEY[0:-4] + obj_id.to_bytes(4, "big")
+
+        if se_crt_token:
+            # Load the certificate from the secure element.
+            certfile = se_dev.read(0x65, 412)
 
     if keyfile is None or "token" not in keyfile:
         # Use MicroPython/CPython SSL to wrap socket.
@@ -58,6 +103,9 @@ def wrap_socket(sock, ssl_params={}):
             ctx.set_ciphers(ciphers)
         if cafile is not None or cadata is not None:
             ctx.load_verify_locations(cafile=cafile, cadata=cadata)
+        if sys_micropython and se_key_token:
+            # Set alternate ECDSA sign function.
+            ctx._context.ecdsa_sign_callback = ecdsa_sign_callback
         return ctx.wrap_socket(sock, server_hostname=hostname)
     else:
         # Use M2Crypto to load key and cert from HSM.