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Re: Strong PRNGs
>Message-Id: <[email protected]>
>Subject: Re: Strong PRNGs
>Date: Wed, 06 Oct 1993 10:32:26 -0400
>From: "Perry E. Metzger" <[email protected]>
>Carl Ellison says:
>> I can think of two:
>>
>> 1. a long-period PRNG (like subtract-with-carry) feeding a
>> cryptographically strong hash function (perhaps triple-DES
>> in ECB mode with both key nad input taken from the PRNG
>> and output becoming the new PRNG output);
>
>What would the point of using this for a one time pad be, though? Why
>not just use triple-DES and be done with the bulk and complexity?
I'm not advocating it as a replacement for triple-DES. I was answering
a question.
I have many uses for random numbers and none of them is XOR encryption.
However, I can even see a point for using this for XOR encryption [I prefer
not to call anything using a PRNG One-Time-Pad]. I can see two points,
even:
1. You might have traffic which operates in very high speed bursts
(faster than your triple-DES can go) but for which the average
throughput is well within the speed of your triple-DES. So, you
keep your PRNG/DES grinding and building a buffer of bytes to be
used, then you use them at high speed during the burst.
2. Knuth's Algorithm M (from someone else) mixes two PRNG streams and
the result is stronger than either of the two sources. I haven't
read the paper he references, so I don't know how much stronger,
but if there's any strength to be gained, someone might want to use
it.
- Carl