source-engine/mathlib/IceKey.cpp

// Purpose: C++ implementation of the ICE encryption algorithm.
//			Taken from public domain code, as written by Matthew Kwan - July 1996
//			http://www.darkside.com.au/ice/

#if !defined(_STATIC_LINKED) || defined(_SHARED_LIB)

#include "mathlib/IceKey.H"
#include "tier0/memdbgon.h"
#pragma warning(disable: 4244)


	/* Structure of a single round subkey */
class IceSubkey {
    public:
	unsigned long	val[3];
};


	/* The S-boxes */
static unsigned long	ice_sbox[4][1024];
static int		ice_sboxes_initialised = 0;


	/* Modulo values for the S-boxes */
static const int	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 */
static const int	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 */
static const unsigned long	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 */
static const int	ice_keyrot[16] = {
				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.
 */

static unsigned int
gf_mult (
	unsigned int	a,
	unsigned int	b,
	unsigned int	m
) {
	unsigned int	res = 0;

	while (b) {
	    if (b & 1)
		res ^= a;

	    a <<= 1;
	    b >>= 1;

	    if (a >= 256)
		a ^= m;
	}

	return (res);
}


/*
 * Galois Field exponentiation.
 * Raise the base to the power of 7, modulo m.
 */

static unsigned long
gf_exp7 (
	unsigned int	b,
	unsigned int		m
) {
	unsigned int	x;

	if (b == 0)
	    return (0);

	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 unsigned long
ice_perm32 (
	unsigned long	x
) {
	unsigned long		res = 0;
	const unsigned long	*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)
{
	int	i;

	for (i=0; i<1024; i++) {
	    int			col = (i >> 1) & 0xff;
	    int			row = (i & 0x1) | ((i & 0x200) >> 8);
	    unsigned long	x;

	    x = gf_exp7 (col ^ ice_sxor[0][row], ice_smod[0][row]) << 24;
	    ice_sbox[0][i] = ice_perm32 (x);

	    x = gf_exp7 (col ^ ice_sxor[1][row], ice_smod[1][row]) << 16;
	    ice_sbox[1][i] = ice_perm32 (x);

	    x = gf_exp7 (col ^ ice_sxor[2][row], ice_smod[2][row]) << 8;
	    ice_sbox[2][i] = ice_perm32 (x);

	    x = gf_exp7 (col ^ ice_sxor[3][row], ice_smod[3][row]);
	    ice_sbox[3][i] = ice_perm32 (x);
	}
}


/*
 * Create a new ICE key.
 */

IceKey::IceKey (int n)
{
	if (!ice_sboxes_initialised) {
	    ice_sboxes_init ();
	    ice_sboxes_initialised = 1;
	}

	if (n < 1) {
	    _size = 1;
	    _rounds = 8;
	} else {
	    _size = n;
	    _rounds = n * 16;
	}

	_keysched = new IceSubkey[_rounds];
}


/*
 * Destroy an ICE key.
 */

IceKey::~IceKey ()
{
	int	i, j;

	for (i=0; i<_rounds; i++)
	    for (j=0; j<3; j++)
		_keysched[i].val[j] = 0;

	_rounds = _size = 0;

	delete[] _keysched;
}


/*
 * The single round ICE f function.
 */

static unsigned long
ice_f (
	unsigned long	p,
	const IceSubkey		*sk
) {
	unsigned long	tl, tr;		/* Expanded 40-bit values */
	unsigned long	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->val[2] & (tl ^ tr);
	ar = al ^ tr;
	al ^= tl;

	al ^= sk->val[0];		/* XOR with the subkey */
	ar ^= sk->val[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.
 */

void
IceKey::encrypt (
	const unsigned char	*ptext,
	unsigned char		*ctext
) const
{
	int		i;
	unsigned long	l, r;

	l = (((unsigned long) ptext[0]) << 24)
				| (((unsigned long) ptext[1]) << 16)
				| (((unsigned long) ptext[2]) << 8) | ptext[3];
	r = (((unsigned long) ptext[4]) << 24)
				| (((unsigned long) ptext[5]) << 16)
				| (((unsigned long) ptext[6]) << 8) | ptext[7];

	for (i = 0; i < _rounds; i += 2) {
	    l ^= ice_f (r, &_keysched[i]);
	    r ^= ice_f (l, &_keysched[i + 1]);
	}

	for (i = 0; i < 4; i++) {
	    ctext[3 - i] = r & 0xff;
	    ctext[7 - i] = l & 0xff;

	    r >>= 8;
	    l >>= 8;
	}
}


/*
 * Decrypt a block of 8 bytes of data with the given ICE key.
 */

void
IceKey::decrypt (
	const unsigned char	*ctext,
	unsigned char		*ptext
) const
{
	int		i;
	unsigned long	l, r;

	l = (((unsigned long) ctext[0]) << 24)
				| (((unsigned long) ctext[1]) << 16)
				| (((unsigned long) ctext[2]) << 8) | ctext[3];
	r = (((unsigned long) ctext[4]) << 24)
				| (((unsigned long) ctext[5]) << 16)
				| (((unsigned long) ctext[6]) << 8) | ctext[7];

	for (i = _rounds - 1; i > 0; i -= 2) {
	    l ^= ice_f (r, &_keysched[i]);
	    r ^= ice_f (l, &_keysched[i - 1]);
	}

	for (i = 0; i < 4; i++) {
	    ptext[3 - i] = r & 0xff;
	    ptext[7 - i] = l & 0xff;

	    r >>= 8;
	    l >>= 8;
	}
}


/*
 * Set 8 rounds [n, n+7] of the key schedule of an ICE key.
 */

void
IceKey::scheduleBuild (
	unsigned short	*kb,
	int		n,
	const int	*keyrot
) {
	int		i;

	for (i=0; i<8; i++) {
	    int	j;
	    int	kr = keyrot[i];
	    IceSubkey		*isk = &_keysched[n + i];

	    for (j=0; j<3; j++)
		isk->val[j] = 0;

	    for (j=0; j<15; j++) {
		int	k;
		unsigned long	*curr_sk = &isk->val[j % 3];

		for (k=0; k<4; k++) {
		    unsigned short	*curr_kb = &kb[(kr + k) & 3];
		    int	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
IceKey::set (
	const unsigned char	*key
) {
	int		i;

	if (_rounds == 8) {
	    unsigned short	kb[4];

	    for (i=0; i<4; i++)
		kb[3 - i] = (key[i*2] << 8) | key[i*2 + 1];

	    scheduleBuild (kb, 0, ice_keyrot);
	    return;
	}

	for (i=0; i<_size; i++) {
	    int			j;
	    unsigned short	kb[4];

	    for (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);
	    scheduleBuild (kb, _rounds - 8 - i*8, &ice_keyrot[8]);
	}
}


/*
 * Return the key size, in bytes.
 */

int
IceKey::keySize () const
{
	return (_size * 8);
}


/*
 * Return the block size, in bytes.
 */

int
IceKey::blockSize () const
{
	return (8);
}

#endif // !_STATIC_LINKED || _SHARED_LIB