The Wiert Corner – irregular stream of stuff

Normally when calculating hashes in .NET you use the [Wayback/Archive] HashAlgorithm.ComputeHash Method (System.Security.Cryptography) | Microsoft Learn.

This can be slow as [Wayback/Archive] cmcginty showed while answering the question [Wayback/Archive] How to get an MD5 checksum in PowerShell – Stack Overflow by [Wayback/Archive] Luke101 posing a faster solution (in this case for md5, but it can be generalised):

There are a lot of examples online using ComputeHash(). My testing showed this was very slow when running over a network connection. The snippet below runs much faster for me, however your mileage may vary:

$md5 = [System.Security.Cryptography.MD5]::Create("MD5")
$fd = [System.IO.File]::OpenRead($file)
$buf = New-Object byte[] (1024*1024*8) # 8 MB buffer
while (($read_len = $fd.Read($buf,0,$buf.length)) -eq $buf.length){
    $total += $buf.length
    $md5.TransformBlock($buf,$offset,$buf.length,$buf,$offset)
    Write-Progress -Activity "Hashing File" `
       -Status $file -percentComplete ($total/$fd.length * 100)
}

# Finalize the last read
$md5.TransformFinalBlock($buf, 0, $read_len)
$hash = $md5.Hash

# Convert hash bytes to a hexadecimal formatted string
$hash | foreach { $hash_txt += $_.ToString("x2") }
Write-Host $hash_txt

Via my search to figure out if the Chocolatey hash check would be case-insensitive (it indeed is case-insensitive):

• [Wayback/Archive] choco/Get-CheckSumValid.ps1 at develop · chocolatey/choco
• [Wayback/Archive] choco/checksum.exe at develop · chocolatey/choco
• [Wayback/Archive] Improve handling for checksum type · Issue #1018 · chocolatey/choco
• [Wayback/Archive] chocolatey/checksum: Validates MD5/SHA1 CheckSums on the command line.
• [Wayback/Archive] checksum/Program.cs at master · chocolatey/checksum
  

  78               //todo: Wonder if we need to flip this for perf on very large files: http://stackoverflow.com/a/13926809
  79              var hash = hash_util.ComputeHash(File.Open(configuration.FilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite));
  80  
  81              string hash_string = BitConverter.ToString(hash).Replace("-",string.Empty);
  82  
  83              if (string.IsNullOrWhiteSpace(configuration.HashToCheck))
  84              {
  85                  Console.WriteLine(hash_string);
  86                  pause_execution_if_debug();
  87                  Environment.Exit(0);
  88              }
  89  
  90              var result = string.Compare(configuration.HashToCheck, hash_string, ignoreCase: true,culture:CultureInfo.InvariantCulture);
  91  
  92              if (result != 0)
  93              {
  94                  Console.WriteLine("Error - hashes do not match. Actual value was '{0}'.", hash_string);
  95                  Environment.ExitCode = 1;
  96              }
  97              else
  98              {
  99                  Console.WriteLine("Hashes match.");
  100             }

--jeroen