Ïðîãðàììíàÿ ðåàëèçàöèÿ (ÿçûê Ñ)
Ïðèìå÷àíèå: ïðåäïîëàãàåòñÿ ÷òî òèïû int è unsigned èìåþò ðàçìåð 4 áàéòà.
Ïðèìåð ôóíêöèè, ãåíåðèðóþùåé ïîáèòíî ïñåâäîñëó÷àéíóþ ïîñëåäîâàòåëüíîñòü:
// ïðèìèòèâíûé íåïðèâîäèìûé ïîëèíîì äëÿ ôîðìèðîâàíèÿ
// Ì-ïîñëåäîâàòåëüíîñòè ñ ïåðèîäîì (2^11)-1
// fi(x) = 1(+)x^2(+)x^11
unsigned NextMValue(unsigned prev)
{
register unsigned c = 0;
if(prev & (1<<1))
c++;
if(prev & (1<<10))
c++;
return (prev<<1)|(c&1);
}
Íà÷àëüíîå çíà÷åíèå ïàðàìåòðà prev ìîæåò áûòü ëþáûì, îòëè÷íûì îò íóëÿ, íîâûé áèò ïîñëåäîâàòåëüíîñòè õðàíèòñÿ â íóëåâîì áèòå âîçâðàùàåìîãî çíà÷åíèÿ.
Ïðèìåð ôóíêöèè, ïîáèòíî ñæèìàþùåé äâîè÷íóþ ïîñëåäîâàòåëüíîñòü â ñèãíàòóðó:
// ïðèìèòèâíûé íåïðèâîäèìûé ïîëèíîì
// äëÿ âû÷èñëåíèÿ 32-áèòíîé ñèãíàòóðû
// fi(x) = 1(+)x^1(+)x^27(+)x^28(+)x^32
unsigned NextSignature32
(unsigned prev, unsigned newbit)
{
if(prev&(1<<0))
newbit++;
if(prev&(1<<26))
newbit++;
if(prev&(1<<27))
newbit++;
if(prev&(1<<31))
newbit++;
return (prev<<1)|(newbit&1);
}
Äëÿ ãåíåðàöèè ãàììû íà îñíîâàíèè êëþ÷à áóäåì ïðèìåíÿòü ñëåäóþùóþ ôóíêöèþ:
unsigned char * generate_gamma(unsigned char *pw, unsigned pwlen, unsigned gamma_len, unsigned char * gamma = NULL)
{
const
gb_len = 256;
static int
polynomial[] = { 1, 5, 23, 171, 243, 1057, 2047, -1 };
//polynomial[] = { 1, 18, 20, 39, -1 }; // ïåðèîä 2^40 - 1
static unsigned char
buf[gb_len+1];
memset(buf, 0, sizeof(buf));
if(pwlen)
for(int i = 0; i < gb_len; i++)
buf[i+1] = pw[i%pwlen];
else
buf[1] = 1;
if(!gamma)
gamma = new unsigned char [gamma_len];
for(int i = 0; i < gamma_len; i++) {
buf[0] = 0;
for(int j = 0; j < 8; j++) {
register unsigned char newbit = 0;
for(int k = 0; polynomial[k] >= 0; k++) {
register unsigned bit = (polynomial[k]+8-j);
if(buf[bit>>3]&(1<<(bit&7)))
newbit++;
}
buf[0] |= (newbit&1)<<(7-j);
}
memmove(buf+1, buf, gb_len);
gamma[i] = buf[0];
}
return gamma;
}
Ýòà ôóíêöèÿ ìîæåò îïåðèðîâàòü ëþáûì ïîëèíîìîì. Ïðèâåä¸í ïîëèíîì ñòåïåíè 2048, èëè 256 áàéò. Çàäàâàòü ïàðîëü äëèííåå 256 áàéò íå èìååò ñìûñëà, ïîñêîëüêó ýòî íèêàê íå îòðàçèòñÿ íà ãåíåðèðóåìîé ãàììå. Êîíå÷íî ìîæíî ïðåäâàðèòåëüíî ïîäâåðãíóòü ïàðîëü ñâ¸ðòêå, íî âåäü òîãäà äëÿ âñêðûòèÿ ìîæíî áóäåò ïåðåáèðàòü òîëüêî 256 áàéò èç ñâ¸ðòêè, êîòîðûå è èñïîëüçóþòñÿ äëÿ ãåíåðàöèè ãàììû. Ïîëèíîì âçÿò «ñ ïîòîëêà», ïîýòîìó äëÿ íàä¸æíîé ãåíåðàöèè ãàììû ñëåäóåò èñïîëüçîâàòü ïðèìèòèâíûé íåïðèâîäèìûé ïîëèíîì.  êîììåíòàðèÿõ óêàçàí ïðèìèòèâíûé ïîëèíîì ñòåïåíè 40, äëÿ êîòîðîãî âðó÷íóþ áûëà ïðîâåðåíà ïðàâèëüíîñòü ðàáîòû ïðîöåäóðû. Ïðàâäà ìàêñèìàëüíàÿ äëèíà êëþ÷à äëÿ íåãî âñåãî ëèøü ïÿòü áàéò L.
 [1] óêàçûâàëèñü íåäîñòàòêè â ïðèìåíåíèè Ì-ïîñëåäîâàòåëüíîñòåé äëÿ ãåíåðàöèè ãàììû, è ïðåäëàãàëîñü èñïîëüçîâàòü ïîñëåäîâàòåëüíîñòè Ãîëäà, îáðàçóþùèåñÿ ñóììèðîâàíèåì íåñêîëüêèõ Ì-ïîñëåäîâàòåëüíîñòåé.
Äëÿ ïðîñòîòû íàø àëãîðèòì áóäåò ðàáîòàòü ñ áàéòàìè, è ñèãíàòóðà áóäåò âû÷èñëÿòüñÿ ñðàçó äëÿ âñåãî áàéòà.
Äëÿ ñæàòèÿ ïîñëåäîâàòåëüíîñòè â ñèãíàòóðó èñïîëüçóåì èçâåñòíóþ è îïòèìèçèðîâàííóþ ôóíêöèþ crc32 (ïðèëàãàåòñÿ ñ èñõîäíûìè òåêñòàìè):
unsigned crc32tab[] = {
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
};
// polynomial is
// X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
unsigned crc32( unsigned crc, unsigned char *buf, unsigned buflen)
{
for(unsigned i = 0; i < buflen; i++)
crc = crc32tab[(unsigned char)(crc ^ unsigned(buf[i]))] ^ ((crc >> 8) & 0x00ffffff);
return crc;
}
Ôóíêöèè çàøèôðîâêè/ðàñøèôðîâêè:
void encrypt(unsigned char * buf, unsigned buflen, unsigned char * gamma)
{
unsigned prev, next;
unsigned char * pgamma;
// ôàçà 1
// çàùèòà îò èçìåíåíèé â èñõîäíîì òåêñòå
// ñâ¸ðòêà 1 - ïðÿìîé õîä
prev = 0xffffffff;
pgamma = gamma;
for(int i = 0; i < buflen; i++) {
next = crc32(prev, buf+i, 1);
next = crc32(next, pgamma+i, 1); // ãàììèðîâàíèå
buf[i] += prev;
prev = next;
}
// ñâ¸ðòêà 2 - îáðàòíûé õîä
prev = 0xffffffff;
pgamma = gamma+buflen;
for(int i = buflen-1; i >= 0; i--) {
next = crc32(prev, buf+i, 1);
next = crc32(next, pgamma+i, 1); // ãàììèðîâàíèå
buf[i] += prev;
prev = next;
}
// ôàçà 2
// çàùèòà îò èçìåíåíèé â øèôðîâàííîì òåêñòå
// ñâ¸ðòêà 3 - ïðÿìîé õîä
prev = 0xffffffff;
pgamma = gamma+(buflen<<1);
for(int i = 0; i < buflen; i++) {
buf[i] += prev;
prev = crc32(prev, buf+i, 1);
prev = crc32(prev, pgamma+i, 1); // ãàììèðîâàíèå
}
// ñâ¸ðòêà 4 - îáðàòíûé õîä
prev = 0xffffffff;
pgamma = gamma+(buflen<<1)+buflen;
for(int i = buflen-1; i >= 0; i--) {
buf[i] += prev;
prev = crc32(prev, buf+i, 1);
prev = crc32(prev, pgamma+i, 1); // ãàììèðîâàíèå
}
}
void decrypt(unsigned char * buf, unsigned buflen, unsigned char * gamma)
{
unsigned prev, next;
unsigned char * pgamma;
// ðàçâ¸ðòêà 4 - îáðàòíûé õîä
prev = 0xffffffff;
pgamma = gamma+(buflen<<1)+buflen;
for(int i = buflen-1; i >= 0; i--) {
next = crc32(prev, buf+i, 1);
next = crc32(next, pgamma+i, 1); // ãàììèðîâàíèå
buf[i] -= prev;
prev = next;
}
// ðàçâ¸ðòêà 3 - ïðÿìîé õîä
prev = 0xffffffff;
pgamma = gamma+(buflen<<1);
for(int i = 0; i < buflen; i++) {
next = crc32(prev, buf+i, 1);
next = crc32(next, pgamma+i, 1); // ãàììèðîâàíèå
buf[i] -= prev;
prev = next;
}
// ðàçâ¸ðòêà 2 - îáðàòíûé õîä
prev = 0xffffffff;
pgamma = gamma+buflen;
for(int i = buflen-1; i >= 0; i--) {
buf[i] -= prev;
prev = crc32(prev, buf+i, 1);
prev = crc32(prev, pgamma+i, 1); // ãàììèðîâàíèå
}
// ðàçâ¸ðòêà 1 - ïðÿìîé õîä
prev = 0xffffffff;
pgamma = gamma;
for(int i = 0; i < buflen; i++) {
buf[i] -= prev;
prev = crc32(prev, buf+i, 1);
prev = crc32(prev, pgamma+i, 1); // ãàììèðîâàíèå
}
}
Ôóíêöèÿ øèôðîâàíèÿ ôàéëà:
int cryptfile(int encrypt, char *fn, unsigned char *pw, unsigned pwlen)
{
FILE * f = fopen(fn, "r+b");
unsigned char * buf, * gamma;
unsigned buflen;
if(!f)
return -1;
buflen = filelength(f->fd);
buf = new char[buflen];
gamma = generate_gamma(pw, pwlen, buflen<<2);
fread(buf, buflen, 1, f);
if(encrypt)
encrypt(buf, buflen, gamma);
else
decrypt(buf, buflen, gamma);
rewind(f);
fwrite(buf, buflen, 1, f);
memset(buf, 0xff, buflen);
memset(buf, 0, buflen);
memset(gamma, 0xff, buflen<<2);
memset(gamma, 0, buflen<<2);
delete buf;
delete gamma;
fclose(f);
return 0;
}
Ïðîâîäèëñÿ íåáîëüøîé àíàëèç íà ñîâïàäåíèå áàéò â ïðåîáðàçîâàííûõ òàêèì îáðàçîì ôàéëàõ. Äëÿ ÷åòûð¸õ ôàéëîâ, èñõîäíîãî, ñ èçìåí¸ííûì îäíèì áèòîì â íà÷àëå, êîíöå è ñåðåäèíå ôàéëà, ñîâïàäåíèå áàéò (ïîïàðíî, êàæäûé ñ êàæäûì) ñîñòàâèëî ìåíåå 0.5%. Ïîñëå ñæàòèÿ àðõèâàòîðîì RAR âñåõ ÷åòûð¸õ ôàéëîâ â îäèí solid-àðõèâ ðàçìåð êàæäîãî ôàéëà óâåëè÷èëñÿ (âîò òàê ;).  ïðèëàãàåìîé ïðîãðàììå ìîæíî ñàìîñòîÿòåëüíî ïîýêñïåðèìåíòèðîâàòü ñ øèôðîâêîé ðàçëè÷íûõ ôàéëîâ. Èìååòñÿ êîìàíäà ñðàâíåíèÿ äâóõ ôàéëîâ. Ïðè ïðåîáðàçîâàíèè äâóõ ôàéëîâ îíè àâòîìàòè÷åñêè ñðàâíèâàþòñÿ. Ïîïðîáóéòå èçìåíèòü íåñêîëüêî áèò, ïîñìîòðèòå ÷òî áóäåò. Êîìó ìàëî, ìîæåò óñîâåðøåíñòâîâàòü èñõîäíûå òåêñòû è ýêñïåðèìåíòèðîâàòü äàëüøå.
