Abstract
A computer disk drive’s motor speed varies slightly but irregularly, principally because of air turbulence inside the disk’s enclosure. The unpredictability of turbulence is well-understood mathematically; it reduces not to computational complexity, but to information losses. By timing disk accesses, a program can efficiently extract at least 100 independent, unbiased bits per minute, at no hardware cost. This paper has three parts: a mathematical argument tracing our RNG’s randomness to a formal definition of turbulence’s unpredictability, a novel use of the FFT as an unbiasing algorithm, and a “sanity check” data analysis.
Affiliations during this work: MIT Project Athena, MIT Stat. Ctr., MIT LCS, resp.
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Davis, D., Ihaka, R., Fenstermacher, P. (1994). Cryptographic Randomness from Air Turbulence in Disk Drives. In: Desmedt, Y.G. (eds) Advances in Cryptology — CRYPTO ’94. CRYPTO 1994. Lecture Notes in Computer Science, vol 839. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-48658-5_13
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