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RE: key material



So u are suggesting 1024/2048 bits size/length for A to seed the PRNG and then after that the output stream O could be drawn to provide the bits for RSA 1024/2048 bits modulo key materials generation?

A few of us are inclined towards this, but a few of my pals seem to think weirdly. They feel that 64/128 or even 192 bits would have sufficed. Their argument is that the symmetric and asymmetric crypto "strength" would means that such length/size of A would match up. A few years back, Schneier commented in a paper on the comparison of crypto "strength" between symmetric and asymmetric key sizes (something like 80bits symm key is equivalent to 1024bits asymm RSA key). But I really disagree that the crypto strength has anythin to do with RNG. What does everyone think?


From: "Burton M. Strauss III" <BStrauss@xxxxxxx>
To: <vuln-dev@xxxxxxxxxxxxxxxxx>
CC: "Greg Kilford" <greg_kilford@xxxxxxxxxxx>
Subject: RE: key material
Date: Fri, 23 Apr 2004 06:48:46 -0500

Remember, while a PRNG may GENERATE more bits, the initial random pool caps
the total randomness.

Suppose you generate 5 numbers using any PRNG you like. If the seed is only
1 bit(0 or 1), there are only TWO patterns you will see.  Period.  If the
seed is two bits, there are 4 patterns, etc.

This surfaced recently in some of the lottery machines - small seed space
and the machines were frequently reset - meaning that the 'quick pick'
tickets covered only a small % of the number space.

-----Burton

> -----Original Message-----
> From: Greg Kilford [mailto:greg_kilford@xxxxxxxxxxx]
> Sent: Thursday, April 22, 2004 12:29 PM
> To: vuln-dev@xxxxxxxxxxxxxxxxx
> Subject: key material
>
>
> Hi everyone,
>
> I was juz discussing with my pals the other day on the
> appropriate initial
> input bit size to seed a PRNG of the structure below for it to be used to
> generate the random bits for RSA key material of modulus 1024
> bits or 2048
> bits.  Anyone know what would be the ideal length/size of A so
> that there is
> sufficient entropy to generate the key material for RSA 1024/2048
> bits keys?
>
> A: Initial input seed of x bit size and fed into the 3DES x9.17
> PRNG in 64
> bit blocks.
> B: A constant key of 128 bits (112 bits effective). Does not change with
> each loop of output block O.
> C: Initialization vector - 64 bits size with initial fixed value and fed
> back with each loop.
> O: Output of 64 bit block with each loop for RSA 1024/2048 key material.
>
> Initial total of x bits as seed
> (feeding in 64-bit block feed)
>             A
>             |
>            \|/
> x9.17 PRNG   V
> ----------------------
> |                    |
> |                    |<------ B (128bits with 112 bits effective)
> : Constant
> value for all loops
> |                    |
> |       3DES         |
> |                    |
> |                    |<-------
> |                    |       |
> ----------------------       |
>         |          |          | C (64 bit IV) : Initial fixed IV.
> Changed/feedback with every loop.
>         |          |          |
>         |          -----------|
>         |
>        \|/
>         V
>         O
> Output Random Stream
> (in 64 bit blocks)
>
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