At 08:28 PM 7/15/96 +0300, Juri wrote:
Is there somewhere where I could find more information on finding out RNG algorithms or reverse-engineering RNG's, once you have some quantity of random numbers generated by some RNG?
For example a local bank is giving each customer a list with 600 one-time passwords (6-digit decimal numbers), and I believe they use the account number as (one of the) seeds for the RNG. Is there some program that I could use, together with the numbers and possible seed, to try to break the RNG?
If you have some guess about the algorithm being used, you can try it, and if they've chosen a weak algorithm, you may be successful. For instance, if they use a simple Linear Congruential Multiplicative PRNG, X[n+1] = ( a * X[n] + c ) mod m and if you've got a list of 600 one-time passwords, you can get a good approximation to m by taking the largest password and looking for prime numbers slightly higher than it. You can then try solving for a and c. On the other hand, if the account number is large, and each X[n+1] is the low-order 6 digits of Y'[n+1] = MD5(Y[n]) and Y[0] = account number, then it'll be much harder to reverse-engineer. # Thanks; Bill # Bill Stewart +1-415-442-2215 stewarts@ix.netcom.com # http://www.idiom.com/~wcs # Confuse Authority!