C Source Code to Authenticating Microsoft CD Keys

/*
    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) mindrape@goodnet.com
        Donald Staheli (Royce)     staheli@goodnet.com

	Web Page: www.goodnet.com/~staheli

 */

#include 
#include 
#include 
#include 

/* 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 that 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++;
    }

   return (ulCheckSum % 7) ? INVALID_KEY : VALID_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 \n"
	 "    i.e. Microsoft CD Key - CDKey 012-0123456\n"
	 "    i.e. OEM CD Key       - CDKey 01234-OEM-012345-01234\n"
	);
  exit(0);
}


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

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

   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;
     }

}