Inconsistent CRC or Checksum Values on Large Applications

• Microsoft Systems Management Server versions 1.1 and 1.2

SUMMARY

Large application executable files can return different cyclic redundancy check (CRC) values due to unique product identification stamping that occurs when the application is installed. To avoid this inconsistent result, you must provide an offset that starts the CRC calculation past this unique data. This also applies to the calculation of Checksum values.

WORKAROUND

To calculate a CRC or Checksum with the SMS Administrator, do the following:

1. Create a new package and click the Inventory button.

2. Select "Add AND..." or "Add OR...".

3. In the File Properties window, click the ellipse button (...) to the right of File Name.

4. Browse to and select the file you want to calculate the CRC or Checksum of.

5. Choose "Checksum" or "CRC" from the Properties Available list and click Add>.

6. Enter a value in the At Byte field. This is the data offset, or byte position, within the file where the algorithm will begin calculating the sum.

7. Enter a value for the Length field. This is the total number of bytes that are summed.

8. Click the Retrieve button. The value displayed in the CRC-16 (or Checksum) field is your result.

NOTE: This documentation mentions the Filetokn.exe utility which was not included with SMS 1.1. Use the steps listed above to perform the same functions.

Generally, an offset of 10,000 and a length of 10,000 to 50,000 will return a consistent value for most large executable files. Don't forget to consider that the larger the values for the length, the longer it will take to calculate. To really be certain that the value you calculate does not contain any unique data, calculate the CRC or Checksum on the executable file installed from two installations of the same application.

MORE INFORMATION

Large applications like Microsoft Word or even applications from other software developers will often contain a unique product ID stamp at the beginning and/or end of the file data.

For example, Microsoft Word 7.0 uses WINWORD.EXE which is 3,845,120 bytes in size. This file contains unique data within the first 225 bytes of the file and also in the last 245K of the file. In order to retrieve a consistent CRC or Checksum value, use an offset or "At Byte" of at least 250 and a length of one to 3,500,000. This will return the same value for every installation of Microsoft Word 7.0.