Re: IV (some input for you)

--On Montag, 14. Januar 2002 18:52 -0500 Tom Gindin <tgindin@us.ibm.com> 
wrote:

>       Since I'm not a subscriber to xmlenc (maybe I should become one), I
> wandered into this a little inadvertently.  My posting of Friday afternoon
> didn't make it to the group, but I'll send you a copy shortly.  Briefly,
> Christian is right about the behavior of CBC mode, which is an argument
> for XMLENC encouraging CBCC or BC instead - the IV or nonce doesn't go
> far.
>             Tom Gindin

Tom,

we are fighting in different fields:

I say that the Nonce is not necessary for _ALL_ block cipher modes that use 
an IV, because the IV brings entropy into the internal state of the mode 
and the Nonce cannot bring more entropy than the IV. So what I want is the 
Nonce removed from the processing model.

You say that CBC in general is not the best solution because for XML 
Encryption it would be nice to have a cipher with infinite error 
propagation. What you want (as far as I understood) is to introduce new 
block algorithms.

These both topics are independant of each other. Implementors can easily 
introduce a new xenc:EncryptionMethod using an own algorithm URI like

http://www.ibm.com/XML/Encryption/#aes128-cbcc

but the processing model with Nonce handling is something which is nested 
deep in our spec.

From what I see, CBC is not a bad idea as a basic REQUIRED algorithm, 
because it is used very often in existing systems and people have 
experience using it. So I would mandate against _substituting_ CBC through 
other modes like BC or CBCC, because CBC is the workhorse for many existing 
systems.


Christian

Received on Tuesday, 15 January 2002 07:33:40 UTC