# Re: True Random Number Generator

*From*: unruh <unruh@xxxxxxxxxxxxxxxxxxxxxxx>*Date*: Tue, 09 Feb 2010 01:37:23 GMT

On 2010-02-08, Mok-Kong Shen <mok-kong.shen@xxxxxxxxxxx> wrote:

Mok-Kong Shen wrote:

[snip]

....................... The essence of the

point, I suppose, is that it can be a valuable research enquiry to find

efficient and good entropy combiners such that, by inputing a plaintext

and a sufficiently random key stream, one could achieve a resulting

entropy of 1 - epsilon per bit, .................

Just an observation: If one uses a good block cipher like AES to

encrypt, it is common that a single key is used to process a fairly

long plaintext stream. But the key has at most 128 bits of entropy.

Isn't it a miracle that the resulting ciphertext stream (a result

of combination) has very high entropy? Or is it rather the case that

the ciphertext stream doesn't possess much higher entropy per bit

"after all" in comparison with the plaintext stream (the enhancement

of entropy per bit being at most 128 divided by the (commonly

relatively large) total number of bits being processed) and thus the

achieved security, on which one "believes", were actually an illusion

(cf. optical illusions)?

Of course it is. We know the attack. Try every one of the 2^128 keys and

see which one works. That is the 128 bits of entropy. the problem is

that "try all 2^128 keys" is really really tedious. Ie, this indicates

that if done properly, 128 bits of entropy is sufficient to hide any

text you wish, for all practical purposes. (at least for now). 128 bits

of entropy is really a lot of different states.

.

M. K. Shen

**Follow-Ups**:**Re: True Random Number Generator***From:*Mok-Kong Shen

**References**:**Re: True Random Number Generator***From:*jmorton123

**Re: True Random Number Generator***From:*bmearns

**Re: True Random Number Generator***From:*Richard Outerbridge

**Re: True Random Number Generator***From:*Mok-Kong Shen

**Re: True Random Number Generator***From:*Mok-Kong Shen

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