A True Random Number Generator obtains randomness from a physical source rather than solely expanding stored state. Noise source, sampling, conditioning and application interface are distinct parts. Hardware origin alone does not guarantee uniform or independent output bits.
NIST SP 800-90B evaluates an entropy source comprising a noise source, optional conditioning and health tests. The subject is evidenced uncertainty in samples, not merely the number of produced bytes. Naming a physical phenomenon alone supplies no such estimate. [NIST SP 800-90B — Entropy sources, conditioning and health tests]
Conditioning can reduce bias and concentrate available entropy into shorter output. NIST SP 800-90B limits claimed output entropy according to the input and mechanism. A random-looking hash does not itself establish unpredictability of the original samples. [NIST SP 800-90B — Entropy sources, conditioning and health tests]
The Repetition Count Test and Adaptive Proportion Test in NIST SP 800-90B monitor repetitions and unusual sample frequencies. They are not universal proof of security. After detecting persistent failure, the source must not continue delivering output normally. [NIST SP 800-90B — Entropy sources, conditioning and health tests]
NIST SP 800-90B ties evaluation to technical and operating conditions of the particular source. Restart tests complement a long continuous recording. Success for one captured sample cannot automatically cover all devices, environments or firmware changes. [NIST SP 800-90B — Entropy sources, conditioning and health tests]
Intel’s DRNG guide distinguishes RDRAND, which reads deterministic-generator output, from RDSEED, which supplies conditioned entropy values for seeding. A hardware instruction therefore need not directly expose unconditioned physical noise. [Intel DRNG guide — RDRAND, RDSEED and CF]
Intel requires checking CF for both RDRAND and RDSEED: 1 means a result is available, 0 means unavailable. Numeric zero in the destination register is not itself a success check. Instruction support and success of an individual call are different matters. [Intel DRNG guide — RDRAND, RDSEED and CF]
Linux hw_random documentation warns that /dev/hwrng data is not verified by fitness tests in this character interface, and faulty hardware may return bogus data. Reading the device alone therefore proves neither entropy quality nor safe application integration. [Linux kernel — Hardware random number generator interface]
NIST SP 800-90C combines entropy sources and generation mechanisms into complete constructions. A wallet assessment must identify the actual component, version, tests, failures and further processing. Source certification alone neither assesses the entire wallet nor protects a later backup. [NIST SP 800-90C — Complete RBG constructions]
For the clearest picture, read this entry together with Cryptographic Entropy, Random Number Generator, CSPRNG, Entropy Mixing. The reverse links also lead from Entropy Mixing.