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nxp424.py

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+# https://www.nxp.com/docs/en/application-note/AN12196.pdf
+from typing import Tuple
+
+from Cryptodome.Cipher import AES
+from Cryptodome.Hash import CMAC
+
+SV2 = "3CC300010080"
+
+
+def myCMAC(key: bytes, msg: bytes = b"") -> bytes:
+    cobj = CMAC.new(key, ciphermod=AES)
+    if msg != b"":
+        cobj.update(msg)
+    return cobj.digest()
+
+
+def decryptSUN(sun: bytes, key: bytes) -> Tuple[bytes, bytes]:
+    IVbytes = b"\x00" * 16
+
+    cipher = AES.new(key, AES.MODE_CBC, IVbytes)
+    sun_plain = cipher.decrypt(sun)
+
+    UID = sun_plain[1:8]
+    counter = sun_plain[8:11]
+
+    return UID, counter
+
+
+def getSunMAC(UID: bytes, counter: bytes, key: bytes) -> bytes:
+    sv2prefix = bytes.fromhex(SV2)
+    sv2bytes = sv2prefix + UID + counter
+
+    mac1 = myCMAC(key, sv2bytes)
+    mac2 = myCMAC(mac1)
+
+    return mac2[1::2]