Add a utility for encrypting/decrypting NVRAM files.

bemani/protocol/protocol.py

@@ -41,7 +41,7 @@ class EAmuseProtocol:
         self.last_text_encoding: Optional[str] = None
         self.last_packet_encoding: Optional[int] = None
 
-    def _rc4_crypt(self, data: bytes, key: bytes) -> bytes:
+    def rc4_crypt(self, data: bytes, key: bytes) -> bytes:
         """
         Given a data blob and a key blob, perform RC4 encryption/decryption.
 
@@ -58,7 +58,10 @@ class EAmuseProtocol:
 
         # KSA Phase
         for i in range(256):
-            j = (j + S[i] + key[i % len(key)]) & 0xFF
+            if key:
+                j = (j + S[i] + key[i % len(key)]) & 0xFF
+            else:
+                j = (j + S[i]) & 0xFF
             S[i], S[j] = S[j], S[i]
 
         # PRGA Phase
@@ -97,7 +100,7 @@ class EAmuseProtocol:
 
         if key:
             # This is an encrypted old-style packet
-            return self._rc4_crypt(data, key)
+            return self.rc4_crypt(data, key)
 
         # No encryption
         return data

bemani/tests/test_RC4.py

@@ -12,10 +12,10 @@ class TestRC4Cipher(unittest.TestCase):
         encrypted = b"\x04]Q\x11\x0cw\x7fO\xfa\x03\xa3\xdf\xb6\x02\xb7d\x9f\x13U\x19\xc9-j\x96\x15yl\x98\xee_<\xfa\x9b\x8f\xbe}\xf4\x05l5\x0e\xd6"
         proto = EAmuseProtocol()
 
-        cyphertext = proto._rc4_crypt(data, key)
+        cyphertext = proto.rc4_crypt(data, key)
         self.assertEqual(encrypted, cyphertext)
 
-        plaintext = proto._rc4_crypt(cyphertext, key)
+        plaintext = proto.rc4_crypt(cyphertext, key)
         self.assertEqual(data, plaintext)
 
     def test_small_data_random(self) -> None:
@@ -23,10 +23,10 @@ class TestRC4Cipher(unittest.TestCase):
         key = bytes([random.randint(0, 255) for _ in range(16)])
         proto = EAmuseProtocol()
 
-        cyphertext = proto._rc4_crypt(data, key)
+        cyphertext = proto.rc4_crypt(data, key)
         self.assertNotEqual(data, cyphertext)
 
-        plaintext = proto._rc4_crypt(cyphertext, key)
+        plaintext = proto.rc4_crypt(cyphertext, key)
         self.assertEqual(data, plaintext)
 
     def test_large_data_random(self) -> None:
@@ -34,8 +34,8 @@ class TestRC4Cipher(unittest.TestCase):
         key = bytes([random.randint(0, 255) for _ in range(16)])
         proto = EAmuseProtocol()
 
-        cyphertext = proto._rc4_crypt(data, key)
+        cyphertext = proto.rc4_crypt(data, key)
         self.assertNotEqual(data, cyphertext)
 
-        plaintext = proto._rc4_crypt(cyphertext, key)
+        plaintext = proto.rc4_crypt(cyphertext, key)
         self.assertEqual(data, plaintext)

bemani/utils/nvram.py

@@ -0,0 +1,62 @@
+import argparse
+import os
+
+from bemani.protocol import EAmuseProtocol
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="A utility to encrypt or decrypt NVRAM files.")
+    parser.add_argument(
+        "file",
+        help="File to encrypt or decrypt.",
+        type=str,
+    )
+    parser.add_argument(
+        "-o",
+        "--output",
+        default=None,
+        type=str,
+        help="Output to a different file instead of overwriting original.",
+    )
+    parser.add_argument(
+        "--strip-padding",
+        action="store_true",
+        default=False,
+        help="Strip null padding on decryption.",
+    )
+    parser.add_argument(
+        "--add-padding",
+        action="store_true",
+        default=False,
+        help="Add null padding on encryption.",
+    )
+    args = parser.parse_args()
+
+    with open(args.file, "rb") as bfp:
+        data = bfp.read()
+
+    if args.add_padding:
+        off_by = len(data) % 768
+        if off_by != 0:
+            data = data + b"\x00" * (768 - off_by)
+
+        assert (len(data) % 768) == 0
+
+    chunks = [data[x:x + 768] for x in range(0, len(data), 768)]
+    outputs = []
+    proto = EAmuseProtocol()
+
+    for chunk in chunks:
+        outputs.append(proto.rc4_crypt(chunk, b""))
+
+    output = b"".join(outputs)
+    if args.strip_padding:
+        while output[-1] == 0:
+            output = output[:-1]
+
+    with open(args.output or args.file, "wb") as bfp:
+        bfp.write(output)
+
+
+if __name__ == "__main__":
+    main()

nvram

@@ -0,0 +1,12 @@
+#! /usr/bin/env python3
+if __name__ == "__main__":
+    import os
+    path = os.path.abspath(os.path.dirname(__file__))
+    name = os.path.basename(__file__)
+
+    import sys
+    sys.path.append(path)
+    os.environ["SQLALCHEMY_SILENCE_UBER_WARNING"] = "1"
+
+    import runpy
+    runpy.run_module(f"bemani.utils.{name}", run_name="__main__")