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Re: Q: Why IPSEC to be used only in CBC mode & not other like CFB or OFB ?
In message <000b01bf7f84$6873e6a0$2dcd09c0@nig95>, "rupesh" writes:
> I had read nearly all RFC'c of Ipsec , everywhere it talks about CBC mode
> implementation only. why Ipsec should not be used in other modes like CFB or
> OFB ?
> Please anyone can give me answer to above question or forward me a link.....
> Thanks & Regards
> Rupesh
In principle, there's no reason why other modes can't be used. However, any
other mode would need its own security analysis. OFB, for example, is very
dangerous if the key stream ever repeats (which in turn would happen if the
same IV were ever used twice during the lifetime of a given key.
Also note that CFB-64 and OFB-64 still require that the plaintext be a
multiple of 8 bytes, and that any other mode -- say, CFB-8 or OFB-8 -- would
require a considerable increase in processing time.
--Steve Bellovin