can you tell what .Random.seed *was*?

On 5/14/2009 3:36 PM, G. Jay Kerns wrote:

Question:
1) can you tell me what my original set.seed() value was? ?(I wouldn't
be able to figure it out, but maybe someone can)

The only way I know is to test all 2^32 possible values of the seed. ?I
think cryptographers would know faster ways.

2) is it possible *in principle* to figure out what set.seed was,
given the above? ?(OK, being able to figure it out in 2*10^68 years
doesn't count, but within a couple months is acceptable.)

I think the brute force search would take about 4-5 days on my old computer,
so a fast one could do it in a few hours.

3) does the answer change if there is a

remove(.Random.seed)

command right before the save.image() command?

Not with the brute force search. ?The cryptographers would probably be able
to make use of the random seed pretty well.

Now, if the seed was removed just before the values were generated, the seed
would be generated from the system clock. ?If you knew the time that this
occurred approximately, the search could be a lot faster.

On the other hand, if there was an unknown large amount of work between the
time of seed generation and the generation of the values x and y, it would
be much more difficult to brute force the solution, because most of the
values of .Random.seed are not reachable either by the clock method or
set.seed, they are only reachable by lots of calls to the underlying
generator. ?So for each seed value you'd need to do every possible number of
RNG generations before generating x and y.

Duncan Murdoch