Skip to main content

True Random Numbers from Random.org

Much of security relies on randomness - encryption keys should be random and random passwords are more secure than dictionary words or predictable sequences. The problem is, how do we generate a random number?

Well, actually, this is a trick question. The answer is that you can't generate random numbers, but you can observe them. Most programming languages give you a random number generator, so why not just use that? Well, it's not actually a random number generator, but a Pseudo-Random Number Generator (PRNG), or more accurately a Pseudo-Random Sequence Generator (PRSG). Given the same seed value, it will produce the same output every time. Try seeding the random number function in your favourite programming language then run your program a few times. You should see the same numbers coming out each time.

The reason for this is the function used to produce random numbers is just a mathematical formula that takes an input and gives an output. To have a random number out, you need a random starting value. Most will seed themselves on the clock, but this isn't random; it isn't even unpredictable. A simplistic example of a PRNG, as given by Knuth in his seminal books, is as follows:

X = (a*X+c) mod m

Random number = X/m for some suitable large prime number m and fixed values a and c both less than m (indeed c is usually a small number <10).

This can be seeded by setting X to the seed value and will give the same sequence of pseudo-random numbers out, as can be seen. However, it isn't random. If I know your seed value I can recreate your sequence of numbers. If you seed it on the clock it is often possible to work out a window of opportunity and obtain a range of seed values. Admittedly, this could be large, but an exhaustive search of these would be quicker than breaking the code that relies on them in many cases. Recently, a large Linux distribution was found to have a flaw in its key-generation that introduced a major weakness into the RSA public-key codes generated on those machines. This was due to predictability of the keys and a lack of randomness.

So, what can we do? We can observe randomness in the natural world. Random.org uses background white noise as a source of randomness. This gives good randomness and distribution of numbers. They offer several options to generate random numbers, sequences or even passwords. An example of their random number service is given below. I'm not saying that they are the best option or the only option, but you must use truly random numbers in your cryptography and secure systems.

Labels:

Comments

Post a Comment

Popular Posts

Coventry Building Society Grid Card

Coventry Building Society have recently introduced the Grid Card as a simple form of 2-factor authentication. It replaces memorable words in the login process. Now the idea is that you require something you know (i.e. your password) and something you have (i.e. the Grid Card) to log in - 2 things = 2 factors. For more about authentication see this post . How does it work? Very simply is the answer. During the log in process, you will be asked to enter the digits at 3 co-ordinates. For example: c3, d2 and j5 would mean that you enter 5, 6 and 3 (this is the example Coventry give). Is this better than a secret word? Yes, is the short answer. How many people will choose a memorable word that someone close to them could guess? Remember, that this isn't a password as such, it is expected to be a word and a word that means something to the user. The problem is that users cannot remember lots of passwords, so remembering two would be difficult. Also, having two passwords isn't real
Post a Comment
Read more

How Reliable is RAID?

We all know that when we want a highly available and reliable server we install a RAID solution, but how reliable actually is that? Well, obviously, you can work it out quite simply as we will see below, but before you do, you have to know what sort of RAID are you talking about, as some can be less reliable than a single disk. The most common types are RAID 0, 1 and 5. We will look at the reliability of each using real disks for the calculations, but before we do, let's recap on what the most common RAID types are. Common Types of RAID RAID 0 is the Stripe set, which consists of 2 or more disks with data written in equal sized blocks to each of the disks. This is a fast way of reading and writing data to disk, but it gives you no redundancy at all. In fact, RAID 0 is actually less reliable than a single disk, as all the disks are in series from a reliability point of view. If you lose one disk in the array, you've lost the whole thing. RAID 0 is used purely to speed up dis
Post a Comment
Read more

Telephone Systems a Hackable Backdoor?

I have been talking to a company that provides telephone exchanges and services to companies this week on behalf of a client and it has highlighted a worrying backdoor. It turns out that many of these companies have a way to remotely connect to their exchange for support purposes - they can remotely control, configure and troubleshoot your system to get you back up and running. Exchanges often have additional modems in them to allow for remote connections. This is all very well and good from a managed service point of view, but what about the rest of your network? Can this be exploited to gain entry to your network? Quite possibly in some cases - it certainly needs to be included in your security audit and perimeter testing. Talking about a specific company now, they supply the software to monitor and bill phone calls through the exchange. They remotely install, monitor and manage this software. How do they do that? Well, it turns out that they install LogMeIn on your machine. Now t
1 comment
Read more