🚀 go-pugleaf

In article <1992Nov20.195655.147884@watson.ibm.com> uri@watson.ibm.com writes:
>How can it be possible, that the expected time to succeed is 
>not dependent on how often I change keys?


If you know that there's a stereotyped plaintext, you can build a file of
all possible encryptions of it then sort that file by the ciphertext
(record just ciphertext and key in the file).

You would have to change keys faster than I could look up plaintext.  (This
is possible.  The file would be huge (6E17 bytes, or so) and it might take
many seconds to look up a key.)

Of course, if you have a PRNG-driven key change algorithm and use a
different key for every 8 byte round of DES (in CBC mode, of course), then
even my break into the crib at the beginning won't tell me what you're
using for the second key and second 8 bytes.  You could use DES itself (or
IDEA) in CFB mode as the PRNG for generating your keys.

This gets expensive.  The DES key scheduling algorithm takes more time than
a round of encryption.  However, if all you're doing is encrypting text at
human typing speed and have a Sparcstation to do it with....

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-- Carl Ellison						cme@sw.stratus.com
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