Re: [Cfrg] draft-housley-ccm-mode-00.txt

David Wagner wrote:

>>An advantage I can see is the use of the same key for both 
>>authentication and encryption. [...] Using the same key 
>>halves the key storage requirements for an 802.11 base station.
>>
>
>It is easy to achieve the same thing with the standard generic
>composition.  You pick a 128-bit key, and derive the encryption and
>authentication keys separately using a PRF: Ke = F_K(0), Ka = F_K(1).
>This is all very standard, and is done in IPSec and TLS, for instance.
>So I don't see this as an advantage or an disadvantage.
>
In an embedded environment where space and power are very constrained 
(802.11 card) halving the space requirement and reducing the amount of 
key scheduling that needs to be performed can certainly be helpful. Many 
current generation 802.11b cards lose about 40% throughput when WEP is 
enabled. The simpler the better.

Ge'

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