Re: DES & IBM's patents

John Kelsey (kelsey@plnet.net)
Fri, 24 Jul 1998 13:21:42 -0500

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> From: Adam Shostack <adam@homeport.org>
> To: Rich Salz <salzr@certco.com>
> Cc: baldwin@rsa.com; CodherPlunks@toad.com; schneier@counterpane.com
> Subject: Re: DES & IBM's patents
> Date: Friday, July 24, 1998 7:23 AM
 
> Rich Salz wrote:
> | >Um, no. IBM has not enforced their DES patents for any
> | >weird new modes.
> |
> | Is CDMF ("40bit DES") a wierd mode of DES or something new
altogether?
> | They do enforce that patent.
>
> Changing the key scheduling is changing the cipher. Its a DES
> derivative, not a mode. (IMHO, anyway.)

Actually, I believe CDMF is just a specific way to choose a DES key,
which has 40 bits of strength but doesn't have some subset of its
bits always set to zero. I don't believe CDMF does anything weird to
the DES key schedule internals.
 
> Adam
>
>
> --
> "It is seldom that liberty of any kind is lost all at once."
> -Hume
>
--John Kelsey, kelsey@counterpane.com / kelsey@plnet.net
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