verifyHash.ps1

<#
.SYNOPSIS
An interactive script used to validate the integrity of a file against its published cryptographic hash value.

.DESCRIPTION
The script will prompt for three inputs:

    1.) A file must be selected via the file picker.

    2.) The known hash value must be provided.
    
    3.) The algorithm used to calculate the hash values must be specified.
    
        Accepted, case-insensitve values are SHA1, SHA256, SHA384, SHA512,
        MACTripleDES, MD5, and RIPEMD160.
#>

Add-Type -AssemblyName System.Windows.Forms

"Choose a file..."

$file = New-Object System.Windows.Forms.OpenFileDialog -Property @{ 
    InitialDirectory = [Environment]::GetFolderPath('MyComputer') 
    Filter = 'All (*.*)|*.*'
}
$null = $file.ShowDialog()

$knownHash = Read-Host "What's the file's known hash?"
$algo = Read-Host "What algorithm was used to calculate this hash?"

$fileHash = Get-FileHash $file.FileName -Algorithm $algo

if ( $fileHash.Hash -eq $knownHash )
{
	Write-Output "Hashes match!"
}
else
{
	Write-Warning -Message "Hash mismatch! Confirm file integrity and/or known hash.`r`n`r`nExiting..."
}