IceKey.cpp

/*
 * C++ implementation of the ICE encryption algorithm.
 *
 * Written by Matthew Kwan - July 1996
 */

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *
 * The C++ ICE Encryption Class
 *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *Synopsis
 *
 *    #include <IceKey.H>
 *
 *    IceKey::IceKey (int level)
 *
 *    IceKey::~IceKey ();
 *
 *    void IceKey::set (const unsigned char *key);
 *
 *    void IceKey::encrypt (const unsigned char *plaintext, unsigned char *ciphertext) const;
 *
 *    void IceKey::decrypt (const unsigned char *ciphertext, unsigned char *plaintext) const;
 *
 *    int IceKey::keySize () const;
 *
 *    int IceKey::blockSize () const;
 *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 *Description
 *
 *The IceKey class is used for encrypting and decrypting 64-bit blocks of data with
 *the ICE (Information Concealment Engine) encryption algorithm.
 *
 *The constructor creates a new IceKey object that can be used to encrypt and decrypt
 *data. The level of encryption determines the size of the key, and hence its speed.
 *Level 0 uses the Thin-ICE variant, which is an 8-round cipher taking an 8-byte key.
 *This is the fastest option, and is generally considered to be at least as secure as
 *DES, although it is not yet certain whether it is as secure as its key size.
 *
 *For levels n greater than zero, a 16n-round cipher is used, taking 8n-byte keys.
 *Although not as fast as level 0, these are very very secure.
 *
 *Before an IceKey can be used to encrypt data, its key schedule must be set with the
 *set() member function. The length of the key required is determined by the level,
 *as described above.
 *
 *The member functions encrypt() and decrypt() encrypt and decrypt respectively data
 *in blocks of eight chracters, using the specified key.
 *
 *Two functions keySize() and blockSize() are provided which return the key and block
 *size respectively, measured in bytes. The key size is determined by the level, while
 *the block size is always 8.
 *
 *The destructor zeroes out and frees up all memory associated with the key.
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

#include "IceKey.h"


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

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


	/* Modulo values for the S-boxes */
	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 */
	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 */
	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 */
	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.
	 */

	unsigned int gf_mult(register unsigned int a, register unsigned int b, register unsigned int m)
	{
		register 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.
	 */

	unsigned long gf_exp7(register unsigned int b, unsigned int m)
	{
		register 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.
	 */

	unsigned long ice_perm32(register unsigned long	x)
	{
		register unsigned long res = 0;
		register 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.
	 */

	void ice_sboxes_init()
	{
		register 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.
 */
namespace {
	unsigned long ice_f(register 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
{
	register int i;
	register 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
{
	register int i;
	register 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++) {
	    register int j;
	    register 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++) {
		register int k;
		unsigned long *curr_sk = &isk->val[j % 3];

		for (k = 0; k < 4; k++) {
		    unsigned short *curr_kb = &kb[(kr + k) & 3];
		    register 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);
}