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libcruft-util/crypto/ice.cpp

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/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2016 Danny Robson <danny@nerdcruft.net>
*/
// Derived from Mathew Kwan's 1996 C++ public domain implementation of ICE:
// http://www.darkside.com.au/ice/
//
// M. Kwan, The Design of the ICE Encryption Algorithm, proceedings of Fast
// Software Encryption - Fourth International Workshop, Haifa, Israel,
// Springer-Verlag, pp. 69-82, 1997
#include "./ice.hpp"
#include "../endian.hpp"
#include "../debug.hpp"
#include <cstdint>
///////////////////////////////////////////////////////////////////////////////
/*
* C++ implementation of the ICE encryption algorithm.
*
* Written by Matthew Kwan - July 1996
*/
/* The S-boxes */
static uint32_t ice_sbox[4][1024];
static bool ice_sboxes_initialised = false;
/* Modulo values for the S-boxes */
static
constexpr
uint_fast16_t
ice_smod[4][4] = {
{333, 313, 505, 369},
{379, 375, 319, 391},
{361, 445, 451, 397},
{397, 425, 395, 505}
};
/* XOR values for the S-boxes */
constexpr
uint8_t
ice_sxor[4][4] = {
{0x83, 0x85, 0x9b, 0xcd},
{0xcc, 0xa7, 0xad, 0x41},
{0x4b, 0x2e, 0xd4, 0x33},
{0xea, 0xcb, 0x2e, 0x04}
};
/* Permutation values for the P-box */
constexpr
uint32_t
ice_pbox[32] = {
0x00000001, 0x00000080, 0x00000400, 0x00002000,
0x00080000, 0x00200000, 0x01000000, 0x40000000,
0x00000008, 0x00000020, 0x00000100, 0x00004000,
0x00010000, 0x00800000, 0x04000000, 0x20000000,
0x00000004, 0x00000010, 0x00000200, 0x00008000,
0x00020000, 0x00400000, 0x08000000, 0x10000000,
0x00000002, 0x00000040, 0x00000800, 0x00001000,
0x00040000, 0x00100000, 0x02000000, 0x80000000
};
/* The key rotation schedule */
constexpr
std::array<uint_fast8_t,8>
ice_keyrot[2] = {
{ 0, 1, 2, 3, 2, 1, 3, 0, },
{ 1, 3, 2, 0, 3, 1, 0, 2, },
};
/*
* 8-bit Galois Field multiplication of a by b, modulo m.
* Just like arithmetic multiplication, except that additions and
* subtractions are replaced by XOR.
*/
template <typename T>
static
T
gf_mult (T a, T b, const T m)
{
T res = 0;
while (b) {
if (b & 1u)
res ^= a;
a <<= 1u;
b >>= 1u;
if (a >= 256)
a ^= m;
}
return res;
}
/*
* Galois Field exponentiation.
* Raise the base to the power of 7, modulo m.
*/
template <typename T>
static
T
gf_exp7 (const T b,
const T m)
{
if (b == 0)
return 0;
T x;
x = gf_mult (b, b, m);
x = gf_mult (b, x, m);
x = gf_mult (x, x, m);
return gf_mult (b, x, m);
}
/*
* Carry out the ICE 32-bit P-box permutation.
*/
static
uint32_t
ice_perm32 (uint32_t x)
{
uint32_t res = 0;
const uint32_t *pbox = ice_pbox;
while (x) {
if (x & 1)
res |= *pbox;
pbox++;
x >>= 1;
}
return res;
}
/*
* Initialise the ICE S-boxes.
* This only has to be done once.
*/
static
void
ice_sboxes_init (void)
{
for (unsigned i = 0; i < 1024; i++) {
const uint_fast16_t col = (i >> 1) & 0xff;
const uint_fast16_t row = (i & 0x1) | ((i & 0x200) >> 8);
for (unsigned j = 0; j < 4; ++j) {
const auto p = gf_exp7<uint_fast16_t> (
col ^ ice_sxor[j][row],
ice_smod[j][row]
) << (24 - j * 8);
ice_sbox[j][i] = ice_perm32 (static_cast<uint32_t>(p));
}
}
}
/*
* Create a new ICE key.
*/
ice::ice (unsigned n,
const uint64_t *key_first,
const uint64_t *key_last)
{
if (!ice_sboxes_initialised) {
ice_sboxes_init ();
ice_sboxes_initialised = true;
}
if (n < 1) {
m_size = 1;
m_rounds = 8;
} else {
m_size = n;
m_rounds = n * 16;
}
m_schedule.resize (m_rounds);
set (key_first, key_last);
}
/*
* Destroy an ICE key.
*/
ice::~ice ()
{
for (auto &s: m_schedule)
std::fill (std::begin (s), std::end (s), 0);
m_rounds = m_size = 0;
}
/*
* The single round ICE f function.
*/
static
uint32_t
ice_f (uint32_t p, const ice::subkey_t &sk)
{
uint_fast64_t tl, tr; /* Expanded 40-bit values */
uint_fast64_t al, ar; /* Salted expanded 40-bit values */
/* Left half expansion */
tl = ((p >> 16) & 0x3ff) | (((p >> 14) | (p << 18)) & 0xffc00);
/* Right half expansion */
tr = (p & 0x3ff) | ((p << 2) & 0xffc00);
/* Perform the salt permutation */
// al = (tr & sk->val[2]) | (tl & ~sk->val[2]);
// ar = (tl & sk->val[2]) | (tr & ~sk->val[2]);
al = sk[2] & (tl ^ tr);
ar = al ^ tr;
al ^= tl;
al ^= sk[0]; /* XOR with the subkey */
ar ^= sk[1];
/* S-box lookup and permutation */
return (
ice_sbox[0][al >> 10] | ice_sbox[1][al & 0x3ff]
| ice_sbox[2][ar >> 10] | ice_sbox[3][ar & 0x3ff]
);
}
/*
* Encrypt a block of 8 bytes of data with the given ICE key.
*/
uint64_t
ice::encrypt (const uint64_t _ptext) const
{
union {
uint64_t pword;
uint8_t pbytes[8];
};
pword = hton (_ptext);
uint32_t l, r;
l = (((uint32_t) pbytes[0]) << 24u)
| (((uint32_t) pbytes[1]) << 16u)
| (((uint32_t) pbytes[2]) << 8u)
| pbytes[3];
r = (((uint32_t) pbytes[4]) << 24u)
| (((uint32_t) pbytes[5]) << 16u)
| (((uint32_t) pbytes[6]) << 8u)
| pbytes[7];
for (unsigned i = 0; i < m_rounds; i += 2) {
l ^= ice_f (r, m_schedule[i]);
r ^= ice_f (l, m_schedule[i + 1]);
}
union {
uint64_t cword;
uint8_t cbytes[8];
};
for (unsigned i = 0; i < 4; i++) {
cbytes[3 - i] = r & 0xff;
cbytes[7 - i] = l & 0xff;
r >>= 8u;
l >>= 8u;
}
return hton (cword);
}
/*
* Decrypt a block of 8 bytes of data with the given ICE key.
*/
uint64_t
ice::decrypt (const uint64_t _ctext) const
{
union {
uint64_t cword;
uint8_t cbytes[8];
};
cword = hton (_ctext);
uint32_t l, r;
l = (((uint32_t) cbytes[0]) << 24u)
| (((uint32_t) cbytes[1]) << 16u)
| (((uint32_t) cbytes[2]) << 8u)
| cbytes[3];
r = (((uint32_t) cbytes[4]) << 24u)
| (((uint32_t) cbytes[5]) << 16u)
| (((uint32_t) cbytes[6]) << 8u)
| cbytes[7];
for (int i = m_rounds - 1; i > 0; i -= 2) {
l ^= ice_f (r, m_schedule[i]);
r ^= ice_f (l, m_schedule[i - 1]);
}
union {
uint64_t pword;
uint8_t pbytes[8];
};
for (unsigned i = 0; i < 4; i++) {
pbytes[3 - i] = r & 0xff;
pbytes[7 - i] = l & 0xff;
r >>= 8;
l >>= 8;
}
return hton (pword);
}
/*
* Set 8 rounds [n, n+7] of the key schedule of an ICE key.
*/
void
ice::scheduleBuild (std::array<uint16_t,4> &kb,
int n,
const std::array<uint_fast8_t,8> &keyrot)
{
for (unsigned i = 0; i < 8; i++) {
int kr = keyrot[i];
subkey_t &isk = m_schedule[n + i];
std::fill (std::begin (isk), std::end (isk), 0);
for (unsigned j = 0; j < 15; j++) {
uint32_t &curr_sk = isk[j % 3];
for (unsigned k = 0; k < 4; k++) {
auto &curr_kb = kb[(kr + k) & 3];
unsigned bit = curr_kb & 1;
curr_sk = (curr_sk << 1) | bit;
curr_kb = (curr_kb >> 1) | ((bit ^ 1) << 15);
}
}
}
}
/*
* Set the key schedule of an ICE key.
*/
void
ice::set (const uint64_t *_key_first, const uint64_t *_key_last)
{
CHECK_EQ ((unsigned)(_key_last - _key_first), m_size);
auto key = reinterpret_cast<const uint8_t*> (_key_first);
if (m_rounds == 8) {
std::array<uint16_t,4> kb;
for (unsigned i = 0; i < 4; i++)
kb[3 - i] = (key[i * 2] << 8) | key[i * 2 + 1];
scheduleBuild (kb, 0, ice_keyrot[0]);
return;
}
for (unsigned i = 0; i < m_size; i++) {
std::array<uint16_t,4> kb;
for (unsigned j = 0; j < 4; j++)
kb[3 - j] = (key[i * 8 + j * 2] << 8) | key[i * 8 + j * 2 + 1];
scheduleBuild (kb, i * 8, ice_keyrot[0]);
scheduleBuild (kb, m_rounds - 8 - i * 8, ice_keyrot[1]);
}
}
/*
* Return the key size, in bytes.
*/
unsigned
ice::key_size () const
{
return (m_size * 8);
}
/*
* Return the block size, in bytes.
*/
unsigned
ice::block_size () const
{
return (8);
}
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