Random Numbers

Don’t get your Pseudo and True Random Numbers Mixed Up

Within cryptography random numbers are used to generate things like encryption keys. If the generation of these keys could be predicted in some way, it may be possible to guess them. The two main types of random number generators are:

• Pseudo-Random Number Generators (PRNGs). This method repeats the random numbers after a given time (periodic). They are fast and are also deterministic, and are useful in producing a repeatable set of random numbers.
• True Random Number Generators (TRNGs). This method generates a true random number, and uses some which is random. One approach is to monitor the movements of a mouse pointer on a screen or from the pauses in key-strokes. Overall the method is generally slow, especially if it involves human interaction, but is non-deterministic and aperiodic.

Normally simulation and modelling applications use PRNG, so that the values generated can be repeated for different runs, while cryptography, lotteries, gambling and games use TRNG, as each value which is selected at random should not repeat or be predictable. Eve could thus guess the key created by the method that Bob uses to generate a key. So, in the generation of encryption keys for public key encryption, user’s are typically asked to generate some random activity…