/*
|  Copyright (C) 2007 Christophe Fergeau <teuf@gnome.org>
|
|  The code in this file is heavily based on the proof-of-concept code
|  written by wtbw
|
| Redistribution and use in source and binary forms, with or without
| modification, are permitted provided that the following conditions are met:
|
|   1. Redistributions of source code must retain the above copyright
| notice, this list of conditions and the following disclaimer.
|   2. Redistributions in binary form must reproduce the above copyright
| notice, this list of conditions and the following disclaimer in the
| documentation and/or other materials provided with the distribution.
|   3. The name of the author may not be used to endorse or promote
| products derived from this software without specific prior written
| permission.
|
| THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
| IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
| OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
| IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
| INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
| BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
| OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
| ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
| OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
| OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
| OF SUCH DAMAGE.
|
|
|  iTunes and iPod are trademarks of Apple
|
|  This product is not supported/written/published by Apple!
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include <glib.h>
#include <string.h>
#include "itdb.h"
#include "db-itunes-parser.h"
#include "itdb_private.h"

static const unsigned char table1[256] = {
	0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 
	0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
	0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 
	0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
	0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 
	0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
	0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 
	0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
	0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 
	0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
	0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 
	0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
	0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 
	0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
	0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 
	0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
	0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 
	0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
	0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 
	0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
	0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 
	0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
	0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 
	0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
	0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 
	0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
	0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 
	0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
	0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 
	0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
	0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 
	0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16
};

static const unsigned char table2[256] = {
	0x52, 0x09, 0x6A, 0xD5, 0x30, 0x36, 0xA5, 0x38, 
	0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB,
	0x7C, 0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 
	0x34, 0x8E, 0x43, 0x44, 0xC4, 0xDE, 0xE9, 0xCB,
	0x54, 0x7B, 0x94, 0x32, 0xA6, 0xC2, 0x23, 0x3D, 
	0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3, 0x4E,
	0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 
	0x76, 0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25,
	0x72, 0xF8, 0xF6, 0x64, 0x86, 0x68, 0x98, 0x16, 
	0xD4, 0xA4, 0x5C, 0xCC, 0x5D, 0x65, 0xB6, 0x92,
	0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9, 0xDA, 
	0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84,
	0x90, 0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 
	0xF7, 0xE4, 0x58, 0x05, 0xB8, 0xB3, 0x45, 0x06,
	0xD0, 0x2C, 0x1E, 0x8F, 0xCA, 0x3F, 0x0F, 0x02, 
	0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A, 0x6B,
	0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 
	0x97, 0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73,
	0x96, 0xAC, 0x74, 0x22, 0xE7, 0xAD, 0x35, 0x85, 
	0xE2, 0xF9, 0x37, 0xE8, 0x1C, 0x75, 0xDF, 0x6E,
	0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5, 0x89, 
	0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B,
	0xFC, 0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 
	0x9A, 0xDB, 0xC0, 0xFE, 0x78, 0xCD, 0x5A, 0xF4,
	0x1F, 0xDD, 0xA8, 0x33, 0x88, 0x07, 0xC7, 0x31, 
	0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC, 0x5F,
	0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 
	0x2D, 0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF,
	0xA0, 0xE0, 0x3B, 0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 
	0xC8, 0xEB, 0xBB, 0x3C, 0x83, 0x53, 0x99, 0x61,
	0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6, 0x26, 
	0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D
};

static const unsigned char fixed[18] = {
    0x67, 0x23, 0xFE, 0x30, 0x45, 0x33, 0xF8, 0x90, 0x99,
    0x21, 0x07, 0xC1, 0xD0, 0x12, 0xB2, 0xA1, 0x07, 0x81
};

#ifndef HAVE_G_CHECKSUM_RESET
#define g_checksum_reset(checksum)                      \
G_STMT_START {                                          \
    g_checksum_free(checksum);                          \
    (checksum) = g_checksum_new (G_CHECKSUM_SHA1);      \
} G_STMT_END
#endif

static int gcd(int a, int b){
    while (TRUE)
    {
        a = a % b;
        if( a == 0 )
            return b;
        b = b % a;
        if( b == 0 )
            return a;
    }
}

static int lcm(int a, int b)
{
    if(a==0 || b==0)
        return 1;

    return (a*b)/gcd(a,b);
}

static unsigned char *generate_key (const unsigned char *firewire_id)
{
    unsigned char *key;
    unsigned char y[16];
    GChecksum *checksum;
    gsize checksum_len;
    int i;

    /* take LCM of each two bytes in the FWID in turn */
    for (i=0; i<4; i++){
        int a = firewire_id[i*2];
        int b = firewire_id[i*2+1];
        int cur_lcm = lcm(a,b);

        unsigned char hi = (cur_lcm & 0xFF00) >> 8;
        unsigned char lo = cur_lcm & 0xFF;

        y[i*4    ] = table1[hi];
        y[i*4 + 1] = table2[hi];
        y[i*4 + 2] = table1[lo];
        y[i*4 + 3] = table2[lo];
    }

    /* hash */
    checksum = g_checksum_new (G_CHECKSUM_SHA1);
    g_checksum_update (checksum, fixed, sizeof (fixed));
    g_checksum_update (checksum, y, sizeof (y));

    key = g_new0 (unsigned char, 64);
    checksum_len = 64;
    g_checksum_get_digest (checksum, key, &checksum_len);
    g_checksum_free (checksum);

    return key;
}

static unsigned char *itdb_compute_hash (const unsigned char *firewire_id,
					 const unsigned char *itdb,
					 unsigned long size, 
					 gsize *len)
{
    unsigned char *key;
    unsigned char *hash;
    GChecksum *checksum;
    int i;
    const gsize CHECKSUM_LEN = g_checksum_type_get_length (G_CHECKSUM_SHA1);
    gsize digest_len;
    
    key = generate_key(firewire_id);
    if (key == NULL) {
	return NULL;
    }

    /* hmac sha1 */
    for (i=0; i < 64; i++)
    {
        key[i] ^= 0x36;
    }

    /* 20 bytes for the checksum, and 1 trailing \0 */
    hash = g_new0 (unsigned char, CHECKSUM_LEN+1);
    checksum = g_checksum_new (G_CHECKSUM_SHA1);
    g_checksum_update (checksum, key, 64);
    g_checksum_update (checksum, itdb, size);
    digest_len = CHECKSUM_LEN;
    g_checksum_get_digest (checksum, hash, &digest_len);
    g_assert (digest_len == CHECKSUM_LEN);

    for (i=0; i < 64; i++)
        key[i] ^= 0x36 ^ 0x5c;

    g_checksum_reset (checksum);
    g_checksum_update (checksum, key, 64);
    g_checksum_update (checksum, hash, digest_len);
    g_checksum_get_digest (checksum, hash, &digest_len);
    g_checksum_free (checksum);
    g_assert (digest_len == CHECKSUM_LEN);

    g_free (key);

    if (len != NULL) {
	*len = digest_len;
    }

    return hash;
}

gboolean itdb_hash58_write_hash (Itdb_Device *device, 
				 unsigned char *itdb_data, 
				 gsize itdb_len,
				 GError **error)
{
    unsigned char firewire_id[20];
    guchar backup18[8];
    guchar backup32[20];
    unsigned char *checksum;
    gsize len;
    MhbdHeader *header;
   
    g_assert (itdb_device_get_checksum_type (device) == ITDB_CHECKSUM_HASH58);

    if (!itdb_device_get_hex_uuid(device, firewire_id)) {
	g_set_error (error, 0, -1, "Couldn't find the iPod firewire ID");
	return FALSE;
    }

    if (itdb_len < 0x6c) {
	g_set_error (error, 0, -1, "iTunesDB file too small to write checksum");
	return FALSE;
    }

    header = (MhbdHeader *)itdb_data;
    g_assert (strncmp (header->header_id, "mhbd", strlen ("mhbd")) == 0);
    memcpy (backup18, &header->db_id, sizeof (backup18));
    memcpy (backup32, &header->unk_0x32, sizeof (backup32));

    /* Those fields must be zero'ed out for the sha1 calculation */
    memset(&header->db_id, 0, sizeof (header->db_id));
    memset(&header->unk_0x32, 0, sizeof (header->unk_0x32));
    memset(&header->hash58, 0, sizeof (header->hash58));

    header->hashing_scheme = GUINT16_FROM_LE (ITDB_CHECKSUM_HASH58);

    checksum = itdb_compute_hash (firewire_id, itdb_data, itdb_len, &len);
    if (checksum == NULL) {
	g_set_error (error, 0, -1, "Failed to compute checksum");
	return FALSE;
    }
    g_assert (len <= sizeof (header->hash58));
    memcpy (&header->hash58, checksum, len);
    g_free (checksum);

    memcpy (&header->db_id, backup18, sizeof (backup18));
    memcpy (&header->unk_0x32, backup32, sizeof (backup32));

    return TRUE;
}

