Merge pull request #99 from troyhacks/pssi_decrypt

Decoding obfuscated PSSI data

pyrekordbox/anlz/file.py

@@ -8,6 +8,7 @@
 from typing import Union
 from .tags import TAGS
 from . import structs
+from construct import Int16ub
 
 logger = logging.getLogger(__name__)
 
@@ -103,6 +104,19 @@ def _parse(self, data: bytes):
             # Get the four byte struct type
             tag_type = tag_data[:4].decode("ascii")
 
+            if tag_type == "PSSI":
+                # deobfuscate tag_data[18:] using xor with verysecretcode+len_entries
+                verysecretcode = bytearray.fromhex(
+                    "CB E1 EE FA E5 EE AD EE E9 D2 E9 EB E1 E9 F3 E8 E9 F4 E1"
+                )
+                len_entries = Int16ub.parse(tag_data[16:])
+                tag_data = bytearray(data[i : i + len(tag_data)])
+                for x in range(len(tag_data[18:])):
+                    decryptmask = verysecretcode[x % len(verysecretcode)] + len_entries
+                    if decryptmask > 255:
+                        decryptmask -= 256
+                    tag_data[x + 18] ^= decryptmask
+
             try:
                 # Parse the struct
                 tag = TAGS[tag_type](tag_data)

pyrekordbox/anlz/structs.py

@@ -195,8 +195,6 @@
 
 # -- Song Structure Tag (PSSI) ---------------------------------------------------------
 
-# FixMe: Implement reverse XOR mask to descramble values
-
 SongStructureEntry = Struct(
     "index" / Int16ub,
     "beat" / Int16ub,
@@ -221,11 +219,11 @@
 PSSI = Struct(
     "len_entry_bytes" /  Const(24, Int32ub),
     "len_entries" / Int16ub,
-    "mood" / Bytes(2),
+    "mood" / Int16ub,
     "u1" / Bytes(6),
-    "end_beat" / Bytes(2),
+    "end_beat" / Int16ub,
     "u2" / Bytes(2),
-    "bank" / Bytes(1),
+    "bank" / Int8ub,
     "u3" / Bytes(1),
     "entries" / Array(this.len_entries, SongStructureEntry),
 )