To compliment my earlier post I have created a short function to generate keys.

Function Generate-key{
Param(
    [validateset(128,192,256)]
    $bits,
    [switch]$COUT,
    $seed
)
    $bytes = $bits/8
    $array = @()
    If($seed){
        1..$bytes | ForEach-Object{
            $array += Get-Random -Minimum 0 -Maximum 255 -SetSeed $seed
        }
    }
    Else{
        1..$bytes | ForEach-Object{
            $array += Get-Random -Minimum 0 -Maximum 255
        }
    }
    If($COUT){
        [string]$retval = ($array -join ',') 
        Return $retval
    }
    Else{
        Return [Byte[]]$Key = $array
    }
}