Tell me more ×
Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. It's 100% free, no registration required.
up vote 0 down vote favorite

I'm looking for some PRNGs and as I have been using Java for a long period of time I thought that the BitInteger class together with the Random class could both generate some large pseudo random numbers. Are the algorithms behind those generations cryptographically secure? Or is it just some sort of a + (b - c) mod d or similiar operation.

share|improve this question
Exactly what algorithms are you considering in the phrase of the question ending in a question mark? – fgrieu Mar 24 '12 at 9:01
4  
Just use the SecureRandom class. – CodesInChaos Mar 24 '12 at 9:49
I was considering the algorithms behind the Random and BigInteger class. – vlad Mar 30 '12 at 11:18
@vlad you were considering wrong :) – owlstead Apr 5 '12 at 1:27

1 Answer

up vote 4 down vote accepted

Presuming this documentation is correct, the answer is no, these numbers are not cryptographically secure. The Random class uses a linear congruential formula with a 48 bit seed. For most purposes it is not enough even if you only require 48 bit security. Given a fairly low number of outputs from a LCG, it is possible to derive the seed, even if only a few bits of each seed iteration are used. That question has been answered here.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.