15 pages (double columns)True Random Number Generators have many uses, in particular they play a key role in security applications and cryptographic algorithms. Our interest lies in the quality of their generated random numbers. More specifically, for such utilizations, a slight deviation of the numbers from a "per- fect" behavior can have disastrous consequences. It is then necessary to devise schemes for the testing of these genera- tors in order to detect non-random properties of their num- bers. Moreover, one should consider them from an attacker point of view and use any means to try to perturbate their good functionnality. In this article we describe such exper- iments and several standard statistical tools for the genera- tors testing. We also present experimental results obtained through the study of a generator embedded in a processor in order to illustrate our methodology. We show that its pertu- bation leads to the apparition of dangerous deviations in its numbers distribution
