On 2013-10-10 (283), at 15:29:33, Stephen Farrell <[email protected]> 
wrote:

>> On 10 Oct 2013, at 17:06, John Kelsey <[email protected]> wrote:
>> 
>> Just thinking out loud....
>> 

[....]

>> c.  Both sides derive the shared key abG, and then use SHAKE512(abG) to 
>> generate an AES key for messages in each direction.

How does this prevent MITM?  Where does G come from?

I'm also leery of using literally the same key in both directions.  Maybe a 
simple transform would suffice; maybe not.

>> d.  Each side keeps a sequence number to use as a nonce.  Both sides use 
>> AES-CCM with their sequence number and their sending key, and keep track of 
>> the sequence number of the most recent message received from the other side. 

If the same key is used, there needs to be a simple way of ensuring the 
sequence numbers can never overlap each other.
__outer



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