What is the most secure seed for random number gen

Question

What are the most secure sources of entropy to seed a random number generator? This question is language and platform independent and applies to any machine on a network. Ideally I'm looking for sources available to a machine in a cloud environment or server provided by a hosting company.

There are two important weaknesses to keep in mind. The use of time for sending a random number generator is a violation of CWE-337. The use of a small seed space would be a violation of CWE-339.

Answer 1

First you need to define the actual use/purpose of the random number generator and why do you think in has to pass so high security standard? The reason I ask is that you mentioned picking it from the could - if you are using it indeed for security purposes then securing the source and the channel to send it around is much more important than anyone's academic knit-picking.

Second element is the size of the actual random numbers you need - big seed is good but only if the number generated is also big - otherwise you'll just be reading the small part of the generated number and that will increase your risk.

Look into reconfigurable ciphers, rather than things like SHA or AES. Here are 2 research papers if you want to read and verify how and why they work:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.97.6594&rep=rep1&type=pdf http://www.springerlink.com/index/q29t6v1p45515186.pdf

Or grab any reconfigurable GOST cipher source code you find on the net and then you an either feed it just any basic seed (like concatenated "ticker" plus a web server node ID (if it's in a web farm) plus a part of response on any internet news site that changes top news all the time or you can feed it highly controlled initial seed (which you can make on your own) and use a light pseudo-random sequence for selecting further cipher configurations. Even NSA can't break that one :-) Since it's always a different cipher. For actual crypto purposes one virtually has to use very controlled initial seed just to be able to replicate the sequence for validation. That's where we go back to first item - securing the source and distribution.

Answer 2

As the consensus is cryptographically strong random numbers must derived form hardware. Some processors have this functionality (Intel chips amonst others). Also sound cards can be used for this by measuring the low-bit fluctuations in the a-d converter.

But due to the hardware needs the is no language and platform independent answer. Pretty much any larger OS will have support for secure random numbers. It is also tricky to implement a good random number generator with good output, since you will have to track the remaining entropy in the pool.

So the first step is to determine what language(s) you will be using. Some do have strong random number support - if this is not the case you would have to abstract the generation to call platform-dependent random sources.

Depending on your security needs be weary of "online" sources since a man-in-the midde can be a serious threat for unauthenticated online sources.