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Re: Size of IV field in DES-CBC mode
> From: colin@nyx10.cs.du.edu (Colin Plumb)
> That's why I suggested expanding a sequence number with a CRC-32: it's a cheap
> and well-understood bit-mixing function which is unlikely to occur in the
> header by accident.
>
> If you specify a source of bits to use to extend the IV, then the IV size can
> be easily varied by negotiation.
>
If you can specify a source of bits to use for the IV, then you don't
need an IV in the packets at all.
My suggestion would be to always use a 32-bit IV, and extend it to 64
with the inverse of the IV. That way, you always get at least a 2-bit
change from a previous IV (counter), and it would very likely not match
changes in the following data (certainly not TCP or UDP).
Yes, a CRC-32 might be better, but I'd rather keep it simple. I'm for
saving both bytes _and_ processing.
Bill.Simpson@um.cc.umich.edu