Added function to ticket.py to return the decrypted Title Key

Also added crypto.py which will manage all crypto-related functionality in the library. Currently only offers a function to decrypt a given Title Key.
ticket.py now creates a list of play limits placed on a title.

requirements.txt

@@ -1 +1,2 @@
 build
+pycryptodome

src/libWiiPy/commonkeys.py

@@ -1,21 +1,25 @@
 # "commonkeys.py" from libWiiPy by NinjaCheetah & Contributors
 # https://github.com/NinjaCheetah/libWiiPy
 
-default_key = 'ebe42a225e8593e448d9c5457381aaf7'
+import binascii
+
+common_key = 'ebe42a225e8593e448d9c5457381aaf7'
 korean_key = '63b82bb4f4614e2e13f2fefbba4c9b7e'
 vwii_key = '30bfc76e7c19afbb23163330ced7c28d'
 
 
-def get_default_key():
-    """Returns the regular Wii Common Key used to encrypt most content."""
-    return default_key
-
-
-def get_korean_key():
-    """Returns the Korean Wii Common Key used to encrypt Korean content."""
-    return korean_key
-
-
-def get_vwii_key():
-    """Returns the vWii Common Key used to encrypt vWii-specific content."""
-    return vwii_key
+def get_common_key(common_key_index):
+    """
+    Returns the specified Wii Common Key based on the index provided.
+    Possible values for common_key_index: 0: Common Key, 1: Korean Key, 2: vWii Key
+    """
+    match common_key_index:
+        case 0:
+            common_key_bin = binascii.unhexlify(common_key)
+        case 1:
+            common_key_bin = binascii.unhexlify(korean_key)
+        case 2:
+            common_key_bin = binascii.unhexlify(vwii_key)
+        case _:
+            raise ValueError("The common key index provided, " + str(common_key_index + ", does not exist."))
+    return common_key_bin

src/libWiiPy/crypto.py

@@ -2,3 +2,22 @@
 # https://github.com/NinjaCheetah/libWiiPy
 #
 # See https://wiibrew.org/wiki/Ticket for details about the TMD format
+
+from .commonkeys import get_common_key
+from Crypto.Cipher import AES
+
+
+def decrypt_title_key(title_key_enc, common_key_index, title_id):
+    """
+    Returns the decrypted version of the encrypted Title Key provided.
+    Requires the index of the common key to use, and the Title ID of the title that the Title Key is for.
+    """
+    # Load the correct common key for the title.
+    common_key = get_common_key(common_key_index)
+    # Calculate the IV by adding 8 bytes to the end of the Title ID.
+    title_key_iv = title_id + (b'\x00' * 8)
+    # Create a new AES object with the values provided.
+    aes = AES.new(common_key, AES.MODE_CBC, title_key_iv)
+    # Decrypt the Title Key using the AES object.
+    title_key = aes.decrypt(title_key_enc)
+    return title_key

src/libWiiPy/ticket.py

@@ -4,6 +4,20 @@
 # See https://wiibrew.org/wiki/Ticket for details about the TMD format
 
 import io
+from .crypto import decrypt_title_key
+from dataclasses import dataclass
+from typing import List
+
+
+@dataclass
+class TitleLimit:
+    """Creates a TitleLimit object that contains the type of restriction and the limit."""
+    # The type of play limit applied. The following types exist:
+    # 0 = None, 1 = Time Limit, 3 = None, 4 = Launch Count
+    limit_type: int
+    # The maximum value of the limit applied.
+    # This is either the number of minutes for a time limit, or the number of launches for a launch limit.
+    maximum_usage: int
 
 
 class Ticket:
@@ -28,9 +42,7 @@ class Ticket:
         self.title_export_allowed: int  # Whether title export is allowed with a PRNG key or not.
         self.common_key_index: int  # Which common key should be used. 0 = Common Key, 1 = Korean Key, 2 = vWii Key
         self.content_access_permissions: bytes  # "Content access permissions (one bit for each content)"
-        #self.limit_type: int  # Type of play limit applied to the title.
-        # 0 = None, 1 = Time Limit, 3 = None, 4 = Launch Count
-        #self.maximum_launches: int  # Maximum for the selected limit type, being either minutes or launches.
+        self.title_limits_list: List[TitleLimit] = []  # List of play limits applied to the title.
         # v1 ticket data
         # TODO: Figure out v1 ticket stuff
         with io.BytesIO(self.ticket) as ticketdata:
@@ -85,6 +97,12 @@ class Ticket:
             # Content access permissions
             ticketdata.seek(0x222)
             self.content_access_permissions = ticketdata.read(64)
+            # Content limits
+            ticketdata.seek(0x264)
+            for limit in range(0, 8):
+                limit_type = int.from_bytes(ticketdata.read(4))
+                limit_value = int.from_bytes(ticketdata.read(4))
+                self.title_limits_list.append(TitleLimit(limit_type, limit_value))
 
     def get_signature(self):
         """Returns the signature of the ticket."""
@@ -131,6 +149,6 @@ class Ticket:
 
     def get_title_key(self):
         """Returns the decrypted title key contained in the ticket."""
-        # TODO
-        return b'\x00'
+        title_key = decrypt_title_key(self.title_key_enc, self.common_key_index, self.title_id)
+        return title_key
 

src/libWiiPy/tmd.py

@@ -29,17 +29,17 @@ class TMD:
         self.version: int  # This seems to always be 0 no matter what?
         self.ca_crl_version: int
         self.signer_crl_version: int
-        self.vwii: int
-        self.ios_tid: str
-        self.ios_version: int
-        self.title_id: str
-        self.content_type: str
-        self.group_id: int  # Publisher of the title
-        self.region: int
+        self.vwii: int  # Whether the title is for the vWii. 0 = No, 1 = Yes
+        self.ios_tid: str  # The Title ID of the IOS version the associated title runs on.
+        self.ios_version: int  # The IOS version the associated title runs on.
+        self.title_id: str  # The Title ID of the associated title.
+        self.content_type: str  # The type of content contained within the associated title.
+        self.group_id: int  # The ID of the publisher of the associated title.
+        self.region: int  # The ID of the region of the associated title.
         self.ratings: int
         self.access_rights: int
-        self.title_version: int
-        self.num_contents: int
+        self.title_version: int  # The version of the associated title.
+        self.num_contents: int  # The number of contents contained in the associated title.
         self.boot_index: int
         self.content_record: List[ContentRecord]
         # Load data from TMD file