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/* crypto.c -- Code for deriving encryption keys.
Copyright (C) 2017 Jakob Tsar-Fox, All Rights Reserved.
This file is part of Nekopack.
Nekopack is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
Nekopack is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with Nekopack. If not, see <http://www.gnu.org/licenses/>. */
#include <stdbool.h>
#include <stdint.h>
#include "crypto.h"
/* Returns the game_key structure for a given game identifier, as
defined in crypto.h */
struct game_key get_key(int game) {
struct game_key k = {0};
switch (game) {
case NEKOPARA_VOLUME_0:
k.master = 0x1548e29c;
k.fallback_initial = 0x9c;
k.fallback_primary = 0xd7;
k.uses_initial = true;
break;
case NEKOPARA_VOLUME_0_STEAM:
k.master = 0x44528b87;
k.fallback_initial = 0x87;
k.fallback_primary = 0x23;
k.uses_initial = true;
break;
case NEKOPARA_VOLUME_1:
k.master = 0x1548e29c;
k.fallback_initial = 0x00;
k.fallback_primary = 0xd7;
k.uses_initial = false;
break;
case NEKOPARA_VOLUME_1_STEAM:
k.master = 0x44528b87;
k.fallback_initial = 0x00;
k.fallback_primary = 0x23;
k.uses_initial = false;
break;
}
return k;
}
/* Generates an initial key for the given key structure and file key. */
uint8_t derive_initial(struct game_key k, uint64_t file_key) {
if (!k.uses_initial) return 0x00;
uint8_t initial = (k.master ^ file_key) & 0xff;
return initial == 0 ? k.fallback_initial : initial;
}
/* Generates a primary key for the given key structure and file key. */
uint8_t derive_primary(struct game_key k, uint64_t file_key) {
uint32_t tmp = k.master ^ file_key;
uint8_t primary = (tmp >> 24 ^ tmp >> 16 ^ tmp >> 8 ^ tmp) & 0xff;
return primary == 0 ? k.fallback_primary : primary;
}
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