system object audit script

function GetFileHash
{
	param(
    ## The path of the file to check
    $Path,

    ## The algorithm to use for hash computation
    [ValidateSet("MD5", "SHA1", "SHA256", "SHA384", "SHA512")]
    $HashAlgorithm = "MD5"
	)

	## Create the hash object that calculates the hash of our file.
	$hashType = [Type] "System.Security.Cryptography.$HashAlgorithm"
	$hasher = $hashType::Create()

	## Create an array to hold the list of files
	$files = @()

	## If they specified the file name as a parameter, add that to the list
	## of files to process
	if($path)
	{
 	   $files += $path
	}
	## Otherwise, take the files that they piped in to the script.
	## For each input file, put its full name into the file list
	else
	{
   		$files += @($input | Foreach-Object { $_.FullName })
	}

	## Go through each of the items in the list of input files
	foreach($file in $files)
	{
    	## Skip the item if it is not a file
    	if(-not (Test-Path $file -Type Leaf)) { continue }

    	## Convert it to a fully-qualified path
    	$filename = (Resolve-Path $file).Path

    	## Use the ComputeHash method from the hash object to calculate
    	## the hash
    	$inputStream = New-Object IO.StreamReader $filename
    	$hashBytes = $hasher.ComputeHash($inputStream.BaseStream)
    	$inputStream.Close()

    	## Convert the result to hexadecimal
    	$builder = New-Object System.Text.StringBuilder
    	$hashBytes | Foreach-Object { [void] $builder.Append($_.ToString("X2")) }

    	## Return a custom object with the important details from the
    	## hashing
		$HashValue = $builder.ToString()
    	$output = New-Object PsObject -Property @{
        	#Path = ([IO.Path]::GetFileName($file));
        	Path = $filename
			HashAlgorithm = $hashAlgorithm;
        	HashValue = $builder.ToString()
    	}

    		Return $HashValue
	}		
}

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