🚀 go-pugleaf

In article <1992Nov11.144908.4035@memstvx1.memst.edu> ujacampbe@memstvx1.memst.edu (James Campbell) writes:
>In article <1992Nov11.173642.29608@ee.eng.ohio-state.edu>, 
>     butzerd@columbia.eng.ohio-state.edu (Dane C. Butzer) writes:
>

[My orignal stuff omitted]

>
>    Dane, do you happen to have a working implementation of the DES handy?
>Good.  Now, make a file of ASCII 0's and encrypt it with some key.  Lookee,
>Lookie, you get a list of random bits!  64 BITS LONG, to be exact, and the
>same list is repeated for the length of the ciphertext file.  That's a big
>reason why cryppies don't use BLOCK CIPHERS like the DES for one-time-pad
>generation.  Of course, it would work fine if you limited your messages to
>a length of 8 bytes... ;-)

Nice sarcasm.  Anyways, I guess I should have specified DES in cipher
feedback mode.  No little 8 byte blocks. :->

>    Using cypher-block chaining would create a more random-LOOKING bit
>stream, but intuition tells me that it would have similar faults, and would
>be reasonably easy to break as well (of course, I could be wrong...).
>    I think you're probably looking at the one-time-pad scheme as a way of
>IMPROVING on the DES.  

Nope.  I was just using DES as an example, since its output in CFM is
unpredictable as well as statisctally random.  The real question was: If
you have a good enough PRNG (or try URNG - unpredictable random number
generator), why is a pseudo one time pad bad?

>Remember, though, that only OTP ciphers that use
>truly random numbers are perfectly secure (in transmission, anyway), and
>using a PRNG will always reduce this security to some degree. 

Yes, but DES (and even RSA) aren't perfectly secure.  They're just
computationally secure.  Only (so far) a true one time pad (based on some
natural random process) is perfectly secure, right?

>To break any
>encryption scheme like this, your adversary need only break the PRNG to do
>it.  If this generator is the DES, then your OTP cipher scheme is no more
>cryptographically secure than the DES itself.
>    Finally, if you're going to use it as a generator, why not just encrypt
>the plaintext with the DES in the first place, and skip the XOR step?

If I were really going to use it for encryption, I'd do just that :-)

Thanks for the reply,

Dane Butzer
butzerd@ee.eng.ohio-state.edu