Generate encryption key (128-bit) for RijndaelManaged

$algorithm = [System.Security.Cryptography.SymmetricAlgorithm]::Create("Rijndael")
$algorithm.set_keysize(128)
$keybytes = $algorithm.get_Key()
$ivbytes = $algorithm.get_IV()
[System.Convert]::ToBase64String($keybytes)
[System.Convert]::ToBase64String($ivbytes)