Microsoft CD Key Validation

CDKey.c

/*
This source code contains a authentication routine that will
validate Microsoft CD Keys.  It is meant that this source code
is a learning tool and not a PIRACY tool.  It is also meant to
show how a large corporation like Microsoft spend MILLIONS of
dollars on development and come up with this protection scheme.

*BorlandC 3.1 was used to compile this successfully.

It is a crime to redistribute these routines in a commercial
venture of any kind without permission or licensing agreement.

C)opyright 1995 Damaged Cybernetics

If you have any questions or comments, please contact the
following ppl via the Internet:

    Donald Moore   (MindRape)    [email protected]
    Donald Staheli (Royce)    [email protected]
    Web Page:          www.goodnet.com/%7Estaheli

*/

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

/* Prototypes */
void help(void);
char ValidateCDKey(char *szKey);

/* definitions for ValidateCDKey function */
#define VALID_KEY 1       /* Yes this is a valid key              */
#define INVALID_KEY 0     /* No this is not a valid key           */
#define INVALID_CHAR -1   /* This key contains invalid characters */
#define INVALID_LENGTH -2 /* This key is the incorrect length     */

/* Length of a Microsoft CD Key, this include the hyphen!            */
#define MS_CD_KEY_LENGTH 11  /* XXX-0123456                          */
#define OEM_CD_KEY_LENGTH 23 /* XXXXX-OEM-0123456-XXXXX              */
#define REAL_KEY_LENGTH 7    /* length of the key is really 7 chars! */
#define REAL_MS_OFFSET 4     /* The MS CD REAL Key offset            */
#define REAL_OEM_OFFSET 10   /* The OEM CD Real Key offset           */

/*
char ValidateCDKey(char *szKey)
ENT: szKey - Char - Key to validate
RET: VALID_KEY - The key is valid
INVALID_KEY    - The key is invalid
INVALID_LENGTH - The key is not a valid CD Key length
INVALID_CHAR   - The key contains invalid characters

   ValidateCDKey will take either a Microsoft or a Microsoft OEM CD Key
   and verify of it's a authentic CD Key which can be used to unlock their
   software when installing.

 */
char ValidateCDKey(char *szKey)
{
    unsigned long ulCheckSum = 0L; /* Hold our checksum value here */
    int iStrLength;                /* Length of the CD Key         */
    int i = 0;                     /* dummy counter                */

    iStrLength = strlen(szKey);

    /* is the key the correct length? */
    if (iStrLength != MS_CD_KEY_LENGTH && iStrLength != OEM_CD_KEY_LENGTH)
        return INVALID_LENGTH;

    /* now move the pointer to the start of the REAL key */
    szKey += iStrLength == MS_CD_KEY_LENGTH ? REAL_MS_OFFSET : REAL_OEM_OFFSET;

    /* now loop thru the CD Key, adding each digit to each other
   * and then mod it by 7.  If it's 0 we have a valid key!
   *
   * btw this routine can be optimized!  It is written for sake of
   * clairity.
   */

    while (i < REAL_KEY_LENGTH)
    {
        if (isdigit(*szKey))
        {
            /* convert each char to it's actual decimal value by
           * subtracting 48 and keep accumlating the values
           */
            ulCheckSum += ((int)*szKey - 48);
        }
        else
            return INVALID_CHAR; /* we hit a NON numeric character       */

        szKey++;
        i++;
    }

    if (!(ulCheckSum % 7))
        return VALID_KEY; /* This IS a valid Microsoft CD Key     */

    return INVALID_KEY; /* This IS NOT a valid Microsoft CD Key */
}

void help(void)
{
    printf("This program will verify whether the CD Key you are using is a\n"
           "a valid Microsoft CD Key.  It is not meant to endorse PIRACY, but\n"
           "to show a big company like Microsoft who has spent millions of\n"
           "dollars and came up with this routine.\n"
           "\nUsage: CDKey <cd key>\n"
           "    i.e. Microsoft CD Key - CDKey 012-0123456\n"
           "    i.e. OEM CD Key       - CDKey 01234-OEM-012345-01234\n");
}

int main(int argc, char *argv[])
{
    puts("Microsoft CD Key Validation\n(C) 1995 Damaged Cybernetics (www.goodnet.com/%7Estaheli)\n");

    if (argc != 2) /* opps user didn't pass any parameters */
    {
        help();
        return 0;
    }

    switch (ValidateCDKey(argv[1]))
    {
    case INVALID_CHAR:
        puts("This key is either not formatted properly or contains alphanumeric characters.");
        break;
    case INVALID_LENGTH:
        puts("This key is neither a valid length for a Microsoft or a OEM CD Key.");
        break;
    case INVALID_KEY:
        puts("This is NOT a valid Microsoft CD Key.");
        break;
    case VALID_KEY:
        puts("This is a VALID Microsoft CD Key.");
        break;
    }

    return 0;
}