length of IV in ESP_NULL cipher

["Tarun Ahuja" <tarun.ahuja@cavium.com>]

Hi all

What should be the length of the IV in case of NULL cipher when using ESP
protocol?

As per RFC 2410
"Because of the stateless nature of the NULL encryption algorithm, it is not
necessary to transmit an IV or similar cryptographic
synchronization data on a per packet (or even a per SA) basis".

Which essentially means the length of the IV should be 0 but FreeSWAN uses a
length of 4bytes IV (equal to blocksize) for NULL cipher.

-Tarun