veekun_pokedex/pokedex/savefile.py
2010-05-25 14:41:15 -07:00

135 lines
4.5 KiB
Python

# encoding: utf8
u"""
Handles reading and encryption/decryption of Pokémon save file data.
See: http://projectpokemon.org/wiki/Pokemon_NDS_Structure
Kudos to LordLandon for his pkmlib.py, from which this module was originally
derived.
"""
import struct
from pokedex.util import permutations
def pokemon_prng(seed):
u"""Creates a generator that simulates the main Pokémon PRNG."""
while True:
seed = 0x41C64E6D * seed + 0x6073
seed &= 0xFFFFFFFF
yield seed >> 16
class PokemonSave(object):
u"""Represents an individual Pokémon, from the game's point of view.
Handles translating between the on-disk encrypted form, the in-RAM blob
(also used by pokesav), and something vaguely intelligible.
XXX: Okay, well, right now it's just encryption and decryption. But, you
know.
"""
def __init__(self, blob, encrypted=False):
u"""Wraps a Pokémon save struct in a friendly object.
If `encrypted` is True, the blob will be decrypted as though it were an
on-disk save. Otherwise, the blob is taken to be already decrypted and
is left alone.
"""
# XXX Sometime this should have an abstract internal representation.
# For now, just store the decrypted version
if encrypted:
# Decrypt it.
# Interpret as one word (pid), followed by a bunch of shorts
struct_def = "I" + "H" * ((len(blob) - 4) / 2)
shuffled = list( struct.unpack(struct_def, blob) )
# Apply standard Pokémon decryption, undo the block shuffling, and
# done
self.reciprocal_crypt(shuffled)
words = self.shuffle_chunks(shuffled, reverse=True)
self.blob = struct.pack(struct_def, *words)
else:
# Already decrypted
self.blob = blob
@property
def as_struct(self):
u"""Returns a decrypted struct, aka .pkm file."""
return self.blob
@property
def as_encrypted(self):
u"""Returns an encrypted struct the game expects in a save file."""
# Interpret as one word (pid), followed by a bunch of shorts
struct_def = "I" + "H" * ((len(self.blob) - 4) / 2)
words = list( struct.unpack(struct_def, self.blob) )
# Apply the block shuffle and standard Pokémon encryption
shuffled = self.shuffle_chunks(words)
self.reciprocal_crypt(shuffled)
# Stuff back into a string, and done
return struct.pack(struct_def, *shuffled)
### Utility methods
shuffle_orders = list( permutations(range(4)) )
@classmethod
def shuffle_chunks(cls, words, reverse=False):
"""The main 128 encrypted bytes (or 64 words) in a save block are split
into four chunks and shuffled around in some order, based on
personality. The actual order of shuffling is a permutation of four
items in order, indexed by the shuffle index. That is, 0 yields 0123,
1 yields 0132, 2 yields 0213, etc.
Given a list of words (the first of which should be the pid), this
function returns the words in shuffled order. Pass reverse=True to
unshuffle instead.
"""
pid = words[0]
shuffle_index = (pid >> 0xD & 0x1F) % 24
shuffle_order = cls.shuffle_orders[shuffle_index]
if reverse:
# Decoding requires going the other way; invert the order
shuffle_order = [shuffle_order.index(i) for i in range(4)]
shuffled = words[:3] # skip the unencrypted stuff
for chunk in shuffle_order:
shuffled += words[ chunk * 16 + 3 : chunk * 16 + 19 ]
shuffled += words[67:] # extra bytes are also left alone
return shuffled
@classmethod
def reciprocal_crypt(cls, words):
u"""Applies the reciprocal Pokémon save file cipher to the provided
list of words.
Returns nothing; the list is changed in-place.
"""
# Apply regular Pokémon "encryption": xor everything with the output of
# the PRNG. First three items are pid/unused/checksum and are not
# encrypted.
# Main data is encrypted using the checksum as a seed
prng = pokemon_prng(words[2])
for i in range(3, 67):
words[i] ^= next(prng)
if len(words) > 67:
# Extra bytes are encrypted using the pid as a seed
prng = pokemon_prng(words[0])
for i in range(67, len(words)):
words[i] ^= next(prng)
return