From: Ionut Florescu <ifloresc_at_stevens.edu>

Date: Tue 31 Jan 2006 - 05:39:56 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jan 31 05:59:14 2006

Date: Tue 31 Jan 2006 - 05:39:56 EST

Thank you for the quick reply, I will look into the R packages. For crashing R try this:

generator.zp=function(x,p)

{a=1:(p-1); b=x^a%%p;

if(all(b[1:(p-2)]!=1)&&(b[p-1]==1)){return(x, " Good ")}
else{return(x, " No Good, try another integer ")}
}

This checks if element x is a generator of the group Z_p. If you try this function for p = 41 and x various increasing values eventually it will crash R. That is what I meant by random, at first I started x=2,3 so on, when I got to 8, R crashed. Now apparently I can get to 15. When I tried again I got to 20.

Ionut Florescu

Duncan Murdoch wrote:

> On 1/30/2006 11:32 AM, Ionut Florescu wrote:

*>> I am a statistician and I come up to an interesting problem in
**>> cryptography. I would like to use R since there are some statistical
**>> procedures that I need to use.
**>> However, I run into a problem when using the modulus operator %%.
**>>
**>> I am using R 2.2.1 and when I calculate modulus for large numbers
**>> (that I need with my problem) R gives me warnings. For instance if
**>> one does:
**>> a=1:40;
**>> 8^a %% 41
**>> one obtains zeros which is not possible since 8 to any power is not a
**>> multiple of 41.
**>> In addition when working with numbers larger that this and with the
**>> mod operator R crashes randomly.
**>
**> Could you keep a record of the random crashes, and see if you can make
**> any of them repeatable? R shouldn't crash. If you can find a
**> repeatable way to make it crash, then that's a bug that needs to be
**> fixed. (If it crashes at random it should still be fixed, but it's so
**> much harder to fix that it's unlikely to happen unless the cases are
**> ones that look likely to come up in normal situations.)
**>
**>
**>>
**>> I believe this is because R stores large integers as real numbers
**>> thus there may be lack of accuracy when applying the modulus operator
**>> and converting back to integers.
**>>
**>> So my question is this: Is it possible to increase the size of memory
**>> used for storing integers? Say from 32 bits to 512 bits (Typical size
**>> of integers in cryptography).
**>
**> No, but there is at least one contributed package that does multiple
**> precision integer arithmetic. I can't remember the name of it right
**> now, but Google should be able to find it for you...
**>
**> Duncan Murdoch
**>>
**>> Thank you, any help would be greatly appreciated.
**>> Ionut Florescu
**>>
**>> ______________________________________________
**>> R-help@stat.math.ethz.ch mailing list
**>> https://stat.ethz.ch/mailman/listinfo/r-help
**>> PLEASE do read the posting guide!
**>> http://www.R-project.org/posting-guide.html
**>
**>
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jan 31 05:59:14 2006

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