• How to Validate the Integrity of a Downloaded File (MD5 or SHA1 Checksums)

    What is Checksum Validation?

    When downloading files from the internet, it's very important to verify that the file you downloaded IS in fact the file you EXPECTED to download.

    Authors of software typically zip up their software and then calculate a "checksum" based on the contents, and post that checksum next to the link to download the file.
    YOU should then re-calculate the checksum on the file AFTER downloading, and compare to be sure that the checksum YOU calculated matches the one posted by the author.
    If they don't match, then you should NOT use the downloaded file, because it may have been tampered with. In such cases you should also report the discrepancy to the author so they can investigate the tampering or fix a mistake.

    Free Tool

    On Windows and Mac computers, you can do this Checksum Validation with a very slick handy free utility called HashTab

    Simply download the utility, run the install, and leave it on your computer for future use.

    How to Use It

    Then, when you download a file from the internet (a Zen Cart distribution zip file, for example), after downloading, validate the file:
    WINDOWS: right-click the file, select Properties, and choose the FileHashes tab to see the calculated hashes.
    MAC: right-click the file, select Services, and choose the FileHashes option to see the calculated hashes.

    Then compare the checksums against the checksums posted on the site from which you downloaded the file.

    If they match, great!
    If not, double-check where you downloaded the file from, and be sure nothing's tampering with your downloads, including maybe even a virus on your computer.

    Linux

    On Linux/Unix computers, you can simply run the "md5" command from a console prompt to do similarly. That's already built-in free with the operating system.