Length of Triple DES algorithm

[Ryan Russell]

You can do 128 by using the 168 variant and setting 40 of the bits to 0
(or any published value.)  Effective length in terms of brute force is
then 128, since 40 of the bits are known to the cracker.

				Ryan

On Tue, 12 Sep 2000, Tim Mather wrote:

>      Triple DES can be implemented in at least two different ways, that I
> am aware of.  Key #1 = key #3 with key #2 being different = 112 bits (2 *
> 56 bits).  "True" triple DES is keys #1, #2, and #3 all being different
> from each other = 168 bits (3 * 56 bits).  How vendors get to different
> lengths is interesting to me.
>      Thanks.
>
> Tim
>
>
>
>
>
> Matthew Harding <matt at NEUROTRAIN.COM>@SECURITYFOCUS.COM> on 09/12/2000
> 07:39:12 AM
>
> Please respond to Matthew Harding <matt at NEUROTRAIN.COM>
>
> Sent by:  VPN Mailing List <VPN at SECURITYFOCUS.COM>
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> To:   VPN at SECURITYFOCUS.COM
> cc:
> Subject:  Length of Triple DES algorithm
>
>
> I have seen references to key length of triple DES ranging anywhere from
> 112 bits to 168, with stops of 128 bits in between.
>
> Is there a well established length for 3DES? Do some vendors implement
> 3DES differently, or is it just a naming convention? Are there any
> security implications between using 3DES with anything less than 168
> bits? I had heard somewhere that the second transform with 3DES doesn't
> actually add anything to the overall security, hence it is only really
> 112 bits of protection.
>
> Any clarifications welcome!
>
> Thanks,
> Matthew
>
> --
> Matthew Harding, Director
> NeuroTrain ATS Inc.
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