Re: [IPsec] IV in ESP packets for AES-CBC and AES-CTR methods

[Dan McDonald <danmcd at sun.com>]

On Mon, May 11, 2009 at 08:22:05PM +0530, ss murthy nittala wrote:
>
> The following sentence present in RFC 3602 creates some doubts whether IV 
> in each packet is mandatory or not?
>
> "Including the IV in each datagram ensures that decryption of each
>  received datagram can be performed, even when some datagrams are
>  dropped, or datagrams are re-ordered in transit."

Nothing vague about it at all!  In fact, this paragraph strengthens the
argument Tero made in his note:  Using the previous cipher-text block is a
Bad Idea (TM).

An IP datagram is self-contained, and the IV is mandatory because you can't
start a CBC decryption without one, and there's no other way to get an IV.

Dan