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Re: Rest of World encryption hardware products?
Alex Alten writes:
> There is no PRNG involved. Every bit, and I mean every bit, used
> to create the final pad is ultimately generated from a Fortezza
> card RNG. This is one of the reasons why it is not a normal
> stream cipher.
[...elided...]
> A finite pad has to be generated on demand by using a unique random
> key and a large finite amount of pre-generated random data
[...elided...]
> In effect each unique pad is created from both static
> and dynamic random data. If the pre-generated random data is
> public, then all the strength resides in the bit length of the
> random key (128 bits here).
Suppose the pre-generated random data _is_ public. Then the TriStrata
system includes some function F that takes the 128-bit unique random key as
input and produces (block-by-block) a keystream of more than 128 bits.
For *any given encryption*, the large finite amount of pre-generated
random data can be treated as part of F. So each encryption uses some
deterministic F to generate the keystream, but (it is claimed that) the
same F will almost never be used twice. I'd call each one of those F's
a PRNG.
Thus it appears that the system uses a long sequence of different PRNGs
over time. An attacker can use the public randomly-generated data to
determine which PRNG was used for any particular encryption. (I'm
assuming the static algorithm underlying the sequence of F's is
available to the attacker, perhaps at a price.)
-Lewis
References: