# File lib/aws/s3/encryption_utils.rb, line 108
      def get_aes_cipher mode, block_mode, key = nil, iv = nil

        # If no key given, default to 256 bit
        cipher_size = (key) ? get_cipher_size(key.length) : 256

        cipher = OpenSSL::Cipher.new("AES-#{cipher_size}-#{block_mode}")

        (mode == :encrypt) ? cipher.encrypt : cipher.decrypt
        cipher.key = key if key
        cipher.iv  = iv  if iv
        cipher
      end