Re: content rather than key?

From: Kai (nospamkai@webmail.co.za)
Date: 03/05/03 

From: "Kai" <nospamkai@webmail.co.za>
Date: Wed, 5 Mar 2003 17:58:36 +0200

"Michiel Buddingh'" <michiel@nospam.com> wrote in message
news:pan.2003.03.05.16.45.48.346022@nospam.com...
> On Wed, 05 Mar 2003 17:00:49 +0200, Kai wrote:
>
> > ... let's see, say an intelligent program can associate more
> > information with the key than the content. My first example
> > was very limited ...
> >
> > say someone uses
> > 'pirate' as a key.
> >
> > the intelligent program would expand this to something like
> >
> > 'ship' 'flag' 'island' 'treasure' 'ocean' 'sword' '1600'
> >
> > now we have a long key
> >
> > shipflagislandtreasureoceanswordseventeenthcentury
> >
> > would that not improve entropy?
>
> IANAC (I am not a cryptographer)
>
> I don't think so. For such an algorithm to work, you'd have to
> choose those words from a limited set, in a predictable manner.
> Furthermore, you'd have to limit the possible input passwords
> as well..
>
> So it would be possible for someone to write an algorithm that
> would simply loop through all the possible passwords, find its
> associated words, and try them.
>
> In short, it would increase the entropy of a string in the same
> way that multiplying by 1000 increases the entropy of a number,
> namely not.
>
> You _could_ choose the words in a random order, and let the de-
> cryption algorithm try all possible combinations of the associated
> words.
>
> This would be comparable to adding a few random bits to the end of
> a number, so I guess that _would_ increase entropy (since the algorithm
> pulls entropy from the (P)RNG used to randomize the sequence, that
> doesn't violate Eivind's assertion).
>
> Given a sufficiently large network of words, and given enough randomness,
> I think such a function _could_ increase the security of `natural'
> passwords, perhaps to a level that brute force attacks become too tedious
> for anyone to bother.
>
> However, such a function would be very slow, especially on decryption,
> and there are easier ways of throwing randomness into an algorithm.
>
> IANAC
>
> > Someone flamed me for the word 'organcially' ... this is what
> > I meant. Obviously this is very simple. you can take it extremely
> > far. Imagine the possibilities to enhance entropy by linking.
> >
> > I guess this must be very stupid.
>
> It doesn't seem stupid to me. Then again, I'm not a cryptographer.
> --
>
> -- michiel
>

I think you got the idea, and successfully showed me what's wrong with it.
You need powerful machines to do the work and huge databases or sources
of information to increase the total number of options.

something in the line of:

cat

... the scientific name of cats or even their dna ... or something?

but the end product would really complicate decrypting or cracking ...?

Kai

Relevant Pages

  • Re: content rather than key?
    ... For such an algorithm to work, ... you'd have to limit the possible input passwords ... it would increase the entropy of a string in the same ... It doesn't seem stupid to me. ...
    (sci.crypt)
  • Re: Fortuna
    ... I certainly agree that information-theoretic security is a stated goal ... >state collisions (therby reducing pool entropy). ... start with any entropy, then information-theoretically secure randomness ... extraction is impossible -- at least in principle. ...
    (Linux-Kernel)
  • Re: real random
    ... Fortuna is, excluding everything they have to say on the matter. ... Are you literally saying that Fortuna is not an algorithm? ... have a source of entropy. ...
    (comp.lang.c)
  • Re: Edible One-Time Pad books
    ... ent told me that the entropy per bit was 8.0 and the compressibility was ... supplied entropy value. ... randomness that would give useful, ...
    (sci.crypt)
  • Re: real random
    ... Feel free to post such an algorithm, ... it as a generator of a stream of numbers, ... You need a genuine source of entropy, ... By suggesting Fortuna (which gathers genuine entropy as it goes), ...
    (comp.lang.c)