Question on CFB variant with c[i-N]

[David Honig]

At 06:46 PM 12/20/97 -0700, Johnson, Michael P (Mike) wrote:
>
>
>>>              cfb    Ciphertext feeback mode
>>>                     c[i] = f1(K, c[i-1]) ^ p[i]
>>>                     p[i] = f1(K, c[i-1]) ^ c[i]
>


Suppose instead of c[i-1] you use c[i-N] where N is say 10. 
How would you prove that this has no security implications?
That 10-way interleaved cfb streams are security-equivalent to
a single cfb stream interleaved with the immediately previous block?



------------------------------------------------------------
      David Honig                   Orbit Technology
     honig at otc.net                  Intaanetto Jigyoubu

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