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Slicing and dicing
A weak key test for 3des was listed in the 3des explicit-iv draft.
It is my understanding that if bytes 1..8 yield a weak key that you toss
that 'slice' and go on, so it would use bytes 9..16.
>Date: Mon, 8 Sep 1997 14:04:31 -0700
>From: Karl Fox <karl@Ascend.COM>
>To: ipsec@tis.com
>Subject: Slicing and dicing
>Reply-To: Karl Fox <karl@Ascend.COM>
>Organization: Ascend Communications
>Sender: owner-ipsec@ex.tis.com
>
>Appendix B of draft -04 of the resolution document says
>
> The key for DES-CBC is derived from the first eight (8) non-weak and
> non-semi-weak (see Appendix A) bytes of SKEYID_e.
>
>If the bytes 1-8 are a weak or semi-weak key, do we then go on to
>bytes 2-9 (I hope not!) or bytes 9-16?
>
>The same appendix later says
>
> The key for 3DES-CBC is the first twenty-four (24) bytes of a key
> derived in the aforementioned pseudo-random function feedback method.
> 3DES-CBC is an encrypt-decrypt-encrypt operation using the first,
> middle, and last eight (8) bytes of the entire 3DES-CBC key.
>
>This means that no weak key test may be done for 3DES-CBC. Was this
>the intent?
>--
>Karl Fox, servant of God, employee of Ascend Communications
>655 Metro Place South, Suite 370, Dublin, Ohio 43017 +1 614 760 4041
>
>
>
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