Random numbers are used extensively in cryptography, e. g. for generation of key material. It is among the more difficult tasks of a cryptographer to determine the quality of a random number source - statistically good random numbers are not necessarily cryptographically secure as well. If an adversary is able to exploit a structure within the stream of random numbers in order to deduce future values with a certain probability, the cryptographic keys generated from these random numbers are vulnerable to attack - even if the cryptographic algorithm itself is secure.
In order to measure the quality of random numbers various tests and criteria have been established that usually analyze the random number sequences numerically. Some of them have also been implemented in CrypTool.
In addition to numerical approaches, structures in random number sequences can also be visualized graphically. CrypTool implements an algorithm that is called phase space visualization which was first implemented by Dan Kaminsky of DoxPara in his program Phentropy (Part of the Paketto Keiretsu Toolkit).
The display options can be adjusted in the dialog 3D Visualization - Options.