[3385] in cryptography@c2.net mail archive
Re: Fwd: Re: r.e. quality of IDEA...
daemon@ATHENA.MIT.EDU (Greg Rose)
Fri Sep 25 17:27:22 1998
To: "David G. Koontz" <koontz@ariolimax.com>
cc: Steve Bellovin <smb@research.att.com>, cryptography@c2.net
In-reply-to: Your message of Thu, 24 Sep 1998 17:34:52 MST.
<360AE52C.41C67EA6@ariolimax.com>
Date: Sat, 26 Sep 1998 07:06:29 +1000
From: Greg Rose <ggr@qualcomm.com>
"David G. Koontz" writes:
>A quick look at the source for IDEA shows that the key for IDEA doesn't
>require
>prescheduling.
It is true that for encryption, there is relatively little benefit from
the precomputed key schedule. For decryption, though... this is not
entirely true. The decryption keys require the modular multiplication
inverses. This can be done by lookup in a 128K table on the fly, but
that's back to real estate. Or they can be computed on the fly, but that
requires the extended Euclidean algorithm. There are probably tradeoffs
in there between these approaches, but it might be worth caching the key
schedules.
Of course you could just encrypt all the time, and never decrypt... :-)
Greg.
Greg Rose INTERNET: ggr@qualcomm.com
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