RE: Choice of ESP alg. for IPS/IPSec - 3DES-CBC vs. 3DES-CBC-I

["Mukund, Shridhar" <Shridhar_Mukund@adaptec.com>]

Paul and Bernard,
 
Comments inline.

-Shridhar Mukund

> -----Original Message-----
> From: Paul Koning [mailto:pkoning@equallogic.com]

>  Bernard> ...Given that 3DES-CBC-I has already been 
>  Bernard> standardized by ANSI,
>  Bernard> it may be feasible to get an IPsec transform document
>  Bernard> written and adopted as a work item by IPsec WG. If this can
>  Bernard> happen, then it would be possible to argue the merits of
>  Bernard> this algorithm versus the other ones under
>  Bernard> consideration. Given the prevalence of 3DES-CBC however, I
>  Bernard> suspect that the argument would be over whether 3DES-CBC-I
>  Bernard> would become a MAY or a SHOULD implement, rather than a
>  Bernard> MUST.
> 
> CBC-I is no less a hardware change than any other new mode.  So it's
> not clear why it would be useful to work on that rather than on other
> new modes.  Perhaps if there aren't IP issues with it?
> 

I agree, this issue needs to be worked in thru the IPSec WG(and saag?)
I have nothing against other new modes, assuming: When AES-CTR is 
approved, AES-CTR becomes MUST and 3DES-CBC is demoted to MAY. On the
other hand, if both are MUST, then there is a problem. There are no IP
issues with CBC-I.

> Given that IPSec acts at the datagram level, you can do interleaving
> on a packet basis.  In a high speed implementation, it is reasonable
> to expect that there are several packets awaiting processing at a
> time.  If so, they can each be run through separate processing
> elements.  So the CBC bottleneck applies within a packet but not
> across packets.  That's not to say that new modes aren't interesting
> -- but it says that you can continue to improve performance in the
> meantime. 
> 

Paul, it is difficult to argue the above issue without getting into
more detail. I do insist that the "additional" and "otherwise 
unnecessary" cost of interleaving on a packet basis is "significant" 
at say 2G thru 10G. Let us take this off-line and follow-up on the IPSec 
reflector. 

-Shridhar Mukund