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RE: A New Triple-DES Key Wrap Algorithm

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At 01:48 PM 2/3/99 -0800, Burt Kaliski wrote:
>Don Johnson's proposal two-pass encryption with triple-DES-CBC is another
>option. It has the advantage of not requiring a separate hash function, and,
>implemented with appropriate settings, resists the birthday attacks on the
>original method.

Burt and Don,

	I'm not sure what Don intended, but I was reminded of one of Ron Rivest's 
papers (in Cryptologia) -- proposing bidirectional encryption when the 
system is easier to break in one direction than the other.

	In the case of CBC mode, one could encrypt a long block twice, as Don 
suggested, but index the blocks in reverse order the second time.  The IV 
could be 0 for both passes.

	I haven't tried analyzing this mode of operation yet, but it has a pleasant 
symmetry.

 - Carl

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+------------------------------------------------------------------+
|Carl M. Ellison         cme@acm.org     http://www.pobox.com/~cme |
|    PGP: 08FF BA05 599B 49D2  23C6 6FFD 36BA D342                 |
+--Officer, officer, arrest that man. He's whistling a dirty song.-+