Generate Cyclic Redundancy Check (CRC) Using CertUtil

A CRC is used to detect any changes to the original data/content, the most common reason being accidental data modification and corruption. CRCs are used to validate integrity, to ensure that the data sent is the data received.

It’s quite easy to create a CRC with tools built into the Windows operating system. Open a command prompt window, browse to the location of your file and run the following command:

CertUtil -hashfile <file_name> MD5

By default CertUtil uses SHA1 if the algorithm is not specified, for this example we’re using MD5. CertUtil supports many different algorithm types.

• MD2
• MD4
• MD5
• SHA1
• SHA256
• SHA384
• SHA512

Once the command has completed successfully CertUtil will output a sequence of numbers and characters, this is the MD5 hash. We will use this hash to validate the integrity of the file once it’s transferred. Once the file is copied we will run the same command and compare the values. If they match the file is valid, if not we know the data was altered. To simplify this process I’ve written a small script in PowerShell that you can leverage.

if ( $(CertUtil -hashfile "<file_name>" MD5) -eq "<hash_from_certutil>" ) { 
  Write-Host "CRC File Integrity Check Passed." -ForegroundColor "Green"

  Write-Host "`nPress any key to exit..."
  $x = $host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown")
  exit 0
}
else {
  Write-Host "CRC File Integrity Check Failed." -ForegroundColor "Red"
  Write-Host "Please re-download file and re-run CRC check."

  Write-Host "`nPress any key to exit..."
  $x = $host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown")
  exit 1
}