CODEWITHSUNDEEP
javasecurityrandom
Ravindra babu
Ravindra babu

Reputation: 38930

JDK 1.7 Secure Random Generator seeding & unpredictability

I am planning to implement MersenneTwister algorithm for random generation. Since it is not secure, looking for setting a seed derived from SecureRandom

SecureRandom secureRandomGenerator = SecureRandom.getInstance("SHA1PRNG");
int seedSize = 100; 
int[] seed = new int[seedSize]; 
for (int i=0; i <seedSize; i++) { 
    seed[i] = secureRandomGenerator.nextInt(Integer.MAX_VALUE); 
}
randomGenerator = new MersenneTwister(seed);

I have two queries

1) Setting a seed to SHA1PRNG is bad idea or good idea?

2) If it is good idea, what is the best way to set seed for SHA1PRNG to improve unpredictability?

Upvotes: 0

Views: 440

Answers (1)

Tagir Valeev
Tagir Valeev

Reputation: 100249

I think if it's just seed, you are using it only once per application launch, so it's not a big security problem. Any good secure random algorithm (including SHA1PRNG) would be nice for the seed. The most problematic place is the Mersenne twister itself. At least it's original implementation is not secure regardless of the seed source as stated in Wikipedia:

The algorithm in its native form is not cryptographically secure. The reason is that observing a sufficient number of iterations (624 in the case of MT19937, since this is the size of the state vector from which future iterations are produced) allows one to predict all future iterations.

Thus regardless of the seed source the Mersenne twister can be compromised if an attacker manages to get enough numbers from it.

Upvotes: 3

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