期刊名称：International Journal of Reconfigurable Computing
印刷版ISSN：1687-7195
电子版ISSN：1687-7209
出版年度：2010
卷号：2010
DOI：10.1155/2010/879281
出版社：Hindawi Publishing Corporation
摘要：The paper deals with true random number generators employing oscillator
rings, namely, with the one proposed by Sunar et al.
in 2007 and enhanced by Wold and Tan in 2009. Our mathematical analysis
shows that both architectures behave identically when
composed of the same number of rings and ideal logic components.
However, the reduction of the number of rings, as proposed
by Wold and Tan, would inevitably cause the loss of entropy.
Unfortunately, this entropy insufficiency is masked
by the pseudo-randomness caused by XOR-ing clock signals having different
frequencies. Our simulation model shows that the
generator, using more than 18 ideal jitter-free rings having slightly
different frequencies and producing only pseudo-randomness,
will let the statistical tests pass. We conclude that a smaller
number of rings reduce the security if the entropy reduction is
not taken into account in post-processing. Moreover, the designer cannot
avoid that some of rings will have the same frequency,
which will cause another loss of entropy. In order to confirm this, we
show how the attacker can reach a state where over
25% of the rings are locked and thus completely dependent. This effect
can have disastrous consequences on the system security.
