wsutil/xtea.c

   1 /* xtea.c
   2  * Implementation of XTEA cipher
   3  * By Ahmad Fatoum <ahmad[AT]a3f.at>
   4  * Copyright 2017 Ahmad Fatoum
   5  *
   6  * Wireshark - Network traffic analyzer
   7  * By Gerald Combs <gerald@wireshark.org>
   8  * Copyright 1998 Gerald Combs
   9  *
  10  * SPDX-License-Identifier: GPL-2.0-or-later
  11  */
  12
  13 #include "xtea.h"
  14
  15 #include <string.h>
  16
  17 #include "pint.h"
  18
  19 void decrypt_xtea_ecb(uint8_t plaintext[8], const uint8_t ciphertext[8], const uint32_t key[4], unsigned num_rounds)
  20 {
  21     unsigned i;
  22     uint32_t v[2], delta = 0x9E3779B9, sum = delta * num_rounds;
  23
  24     v[0] = pntoh32(&ciphertext[0]);
  25     v[1] = pntoh32(&ciphertext[4]);
  26
  27     for (i = 0; i < num_rounds; i++) {
  28         v[1] -= (((v[0] << 4) ^ (v[0] >> 5)) + v[0]) ^ (sum + key[(sum >> 11) & 3]);
  29         sum -= delta;
  30         v[0] -= (((v[1] << 4) ^ (v[1] >> 5)) + v[1]) ^ (sum + key[sum & 3]);
  31     }
  32
  33     v[0] = GUINT32_TO_BE(v[0]);
  34     v[1] = GUINT32_TO_BE(v[1]);
  35
  36     memcpy(plaintext, v, sizeof v);
  37 }
  38
  39 void decrypt_xtea_le_ecb(uint8_t plaintext[8], const uint8_t ciphertext[8], const uint32_t key[4], unsigned num_rounds)
  40 {
  41     unsigned i;
  42     uint32_t v[2], delta = 0x9E3779B9, sum = delta * num_rounds;
  43
  44     v[0] = pletoh32(&ciphertext[0]);
  45     v[1] = pletoh32(&ciphertext[4]);
  46
  47     for (i = 0; i < num_rounds; i++) {
  48         v[1] -= (((v[0] << 4) ^ (v[0] >> 5)) + v[0]) ^ (sum + key[(sum >> 11) & 3]);
  49         sum -= delta;
  50         v[0] -= (((v[1] << 4) ^ (v[1] >> 5)) + v[1]) ^ (sum + key[sum & 3]);
  51     }
  52
  53     v[0] = GUINT32_TO_LE(v[0]);
  54     v[1] = GUINT32_TO_LE(v[1]);
  55
  56     memcpy(plaintext, v, sizeof v);
  57 }
  58
  59 /*
  60  * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
  61  *
  62  * Local variables:
  63  * c-basic-offset: 4
  64  * tab-width: 8
  65  * indent-tabs-mode: nil
  66  * End:
  67  *
  68  * vi: set shiftwidth=4 tabstop=8 expandtab:
  69  * :indentSize=4:tabSize=8:noTabs=true:
  70  */