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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)
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.
       |          |          |
       |          -----------|
Output Random Stream
(in 64 bit blocks)

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