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Re: IVs, summary of discussion
>The IP pseudo hdr is unique and was always a bad idea.
Perhaps it wasn't really necessary, but it hasn't really caused any
damage either. Even without it you'd still have to pass the IP header
addresses (and length, for TCP) up to the transport layer. The only
thing missing from this set to form a pseudoheader is the IP protocol
field, which is a well-known constant anyway. So the inter-layer
communication requirements would be the same.
>Perhaps I'm not considering the right set of numbers, but it seems
>that the 8 byte savings in transmission cost is swamped by the cost of
>security algorithms.
Well, there's no "right" set of numbers, there are lots of different
numbers, some of which are more important to some people than to others.
Here are the numbers for me:
DES encryption speed: 43,459 encryptions/sec (2.8 microseconds/byte)
on a 486-50 in real mode
Line transmission speed: 960 bytes/sec (1.04 ms/byte) over an IS-95
CDMA digital cellular channel.
That's a 371:1 ratio between encryption speed and transmission speed.
Sure, if you use a slow laptop instead of a desktop PC and a V.34
modem instead of a digital cell phone the ratio may decrease to, say,
50:1. And for Ran's channels I wouldn't be surprised if the ratio hit
1000:1. But I think you get my point. For me at least, encryption is
cheap and transmission is expensive (I thought you were the one trying
to convince me of this!)
>I'm not arguing that privacy and authentication cannot be orthogonal, but
>I am saying that one cannot guarantee that they are without considering
>the entire protocol, including key management.
On this point we agree.
Phil
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