/*

The following is the simple algorithm used by Soldier of Fortune II to check the CD-Keys
NOTE: the interesting thing of this algorithm is that the latest 2 chars of each Key
      are a control byte (%02x) calculated on the first 16 bytes of the key

by Luigi Auriemma
e-mail: aluigi@autistici.org
web:    aluigi.org

*/


#define OKKO    "\x00\x00\x01\x01\x00\x00\x01\x01" \
                "\x01\x01\x01\x01\x01\x01\x01\x01" \
                "\x01\x01\x00\x00\x01\x00\x01\x00" \
                "\x00\x01\x00\x01\x01\x00\x01\x00" \
                "\x01\x00\x01\x01\x00\x00\x01\x00"

/* OKKO:           */
/* if 0: ok        */
/* if 1: wrong key */




    char           cdkey[],    // cdkey of 18 chars (0-9, A-Z)
                   *ptr,       // pointer
                   final;      // control byte (last 2 chars of the CD-Key) */
    int            i;          // counter
    unsigned long  ecx,        // register
                   edx;        /* control byte                                      */
                               /* the latest 2 chars of each key are a control byte */
                               /* calculated on the first 16 bytes of the CD-Key    */



    sscanf(cdkey + 16, "%02X", &final);
    edx = 0;
    ptr = cdkey;
    for(i = 0; i < 16; i++) {
        if((*ptr >= 0x61) && (*ptr <= 0x7a)) *ptr += 0xe0;
        ecx = *ptr - 0x33;
        if(ecx > 0x27) break;
        if(OKKO[ecx]) break;
        edx <<= 1;
        edx ^= *ptr;
        ptr++;
    }

    edx &= 0xff;
    if((i == 16) && (edx == final)) fputs("\nYour Cd-Key is OK\n", stdout);
        else fputs("\nYour Cd-Key is invalid\n", stdout);