= Powershell: Function: Get MD5 Hash =

**Summary**: A function to get the MD5 hash of various items and examples on how to use it \\
**Date**: Around 2013 \\
**Refactor**: 22 March 2025: Checked links and formatting. \\
{{tag>powershell}}

> It is based on [[https://github.com/Wintellect/WintellectPowerShell/blob/master/Code/Get-Hash.psm1|this script from WinTellect]].

== Function ==

First step is to create the Get-Hash.psm1 file. This can be a regular textfile and should contain the following lines:
<code powershell>
<#
.SYNOPSIS
    Gets the hash value

.DESCRIPTION
    Gets the hash value of a file or string
    It uses System.Security.Cryptography.HashAlgorithm (http://msdn.microsoft.com/en-us/library/system.security.cryptography.hashalgorithm.aspx)
    and FileStream Class (http://msdn.microsoft.com/en-us/library/system.io.filestream.aspx)

    Written by Josep Martínez Vilà: http://dbadailystuff.com/2013/03/11/get-hash-a-powershell-hash-function/
    Based on: http://blog.brianhartsock.com/2008/12/13/using-powershell-for-md5-checksums/ and some ideas on Microsoft Online Help

.PARAMETER File
    File to get the hash from.

.PARAMETER Text
    Text string to get the hash from

.PARAMETER Algorithm
    Type of hash algorithm to use. Default is SHA1

.EXAMPLE
    C:\PS> Get-Hash "myFile.txt"
    Gets the SHA1 from myFile.txt file. When there's no explicit parameter, it uses -File

.EXAMPLE
    Get-Hash -File "C:\temp\myFile.txt"
    Gets the SHA1 from myFile.txt file

.EXAMPLE
    C:\PS> Get-Hash -Algorithm "MD5" -Text "Hello Wold!"
    Gets the MD5 from a string

.EXAMPLE
    C:\PS> "Hello Wold!" | Get-Hash
    We can pass a string throught the pipeline
#>
function Get-Hash
{
    Param
    (
        [parameter(Mandatory=$true, ValueFromPipeline=$true, ParameterSetName="set1")]
        [String]
        $text,
        [parameter(Position=0, Mandatory=$true, ValueFromPipeline=$false, ParameterSetName="set2")]
        [String]
        $file = "",
        [parameter(Mandatory=$false, ValueFromPipeline=$false)]
        [ValidateSet("MD5", "SHA", "SHA1", "SHA-256", "SHA-384", "SHA-512")]
        [String]
        $algorithm = "SHA1"
    )

    Begin
    {
        $hashAlgorithm = [System.Security.Cryptography.HashAlgorithm]::Create($algorithm)
    }
     Process
     {
        $md5StringBuilder = New-Object System.Text.StringBuilder 50
        $ue = New-Object System.Text.UTF8Encoding

        if ($file){
            try {
                if (!(Test-Path $file)){
                    throw "Test-Path returned false."
                }
            }
            catch {
                throw "Get-Hash - File not found or without permisions: [$file]. $_"
            }

            try {
                [System.IO.FileStream]$fileStream = [System.IO.File]::Open($file, [System.IO.FileMode]::Open);
                $hashAlgorithm.ComputeHash($fileStream) | % { [void] $md5StringBuilder.Append($_.ToString("x2")) }
            }
            catch {
                throw "Get-Hash - Error reading or hashing the file: [$file]"
            }
            finally {
                $fileStream.Close()
                $fileStream.Dispose()
            }
        }
        else {
            $hashAlgorithm.ComputeHash($ue.GetBytes($text)) | % { [void] $md5StringBuilder.Append($_.ToString("x2")) }
        }

        return $md5StringBuilder.ToString()
    }
}
</code>

Now you can use it in your script by first importing the script as a module:
<code>
# Add Get-Hash function
Import-Module g:\scripts\get-hash.psm1
</code>

Now you can create a string, for example based on the VM name with an extra string:
<code powershell>
$stringtohash = $vm.toUpper() + "-go4shift"
$guestpw = (Get-Hash -Algorithm "MD5" -text $stringtohash)
</code>

or like this to add extra parameters after hashing:
<code powershell>
$guestpw = (Get-Hash -Algorithm "MD5" -text $stringtohash) + "!!!"
</code>

Now you can use the password like you would normally do, for example when using the {{{Copy-VMGuestFile}}} commandlet:
<code powershell>
Copy-VMGuestFile -Source $scriptlocation\$script -Destination $guestdir -Force -VM $vm -LocalToGuest -HostUser root -HostPassword $hostpw -GuestUser Administrator -GuestPassword $guestpw
</code>

{{tag>vmware scripts security}}