This page is a map, not a substitute for the deeper guides. Each answer gives the shortest useful explanation and points to the canonical page for the full treatment.
Fundamentals
1. What is a QRNG?
A quantum random number generator obtains unpredictability from measurement of a quantum physical process. A complete QRNG also needs measurement electronics, a defensible model, monitoring and processing before the output is suitable for security use. Start with the flagship guide →
2. Is a QRNG the same as a TRNG?
A QRNG is a type of physical random-number approach whose claimed entropy mechanism is quantum. “TRNG” is broader and is commonly used for physical generators that are not deterministic software generators. Compare PRNG, TRNG and QRNG →
3. Is a QRNG a quantum computer?
No. QRNGs use quantum physical behavior to obtain entropy; they do not need to perform general-purpose quantum computation. What is a QRNG? →
4. Does QRNG replace post-quantum cryptography?
No. PQC addresses cryptographic algorithms threatened by quantum computing. QRNG addresses the source of randomness. They can be complementary, but one does not replace the other. QRNG for PQC →
Entropy
5. What is an entropy source?
It is the component or process that introduces unpredictability into a random-bit-generation system. Read the entropy-source guide →
6. What is min-entropy?
Min-entropy is a conservative measure focused on the most probable outcome: the outcome an optimal first guess would choose. Read the min-entropy guide →
7. Is bit length the same as entropy?
No. A 256-bit string is 256 bits long, but it may contain much less than 256 bits of unpredictability if the generating process is biased, restricted or predictable.
8. What is entropy per sample?
It is a way of expressing how much unpredictability can be credited, under the chosen model and evaluation method, to each raw observation of the source.
9. What is entropy rate?
Entropy rate relates the amount of estimated unpredictability to time or sample throughput. Raw sample rate, entropy rate and final output rate are different quantities.
10. Can conditioning create entropy?
A deterministic conditioning function can improve distributional properties and concentrate existing entropy, but it does not create unpredictability that was absent from its input. Read about conditioning →
SP 800-90
11. What is NIST SP 800-90B?
SP 800-90B specifies design principles, requirements and tests for entropy sources used by random bit generators. SP 800-90B explained →
12. What is SP 800-90A?
SP 800-90A Rev. 1 specifies deterministic random bit generator mechanisms based on cryptographic algorithms.
13. What is SP 800-90C?
SP 800-90C specifies constructions for complete random bit generators that combine components addressed by 90A and 90B. NIST finalized it in September 2025. Compare 90A, 90B and 90C →
14. Does SP 800-90B define a QRNG?
No. It addresses entropy-source assurance. Whether a physical mechanism is genuinely quantum is a separate scientific and implementation claim.
15. Is running the NIST entropy tool the same as NIST validation?
No. NIST's CMVP states that the ESV process runs the entropy assessment tool but also requires additional documentation and review. How validation differs from testing →
IID, non-IID and restart testing
16. What does IID mean?
IID means independent and identically distributed: samples are modeled as having the same distribution and not depending on one another. IID vs non-IID →
17. Should I assume my entropy source is IID?
No. An IID claim needs justification. The NIST entropy-assessment repository explicitly notes that most commonly used entropy sources are not IID.
18. What is a non-IID assessment?
It estimates min-entropy without relying on the stronger IID assumption and therefore uses a more conservative set of estimators for general data.
19. What is restart testing?
Restart testing checks behavior across repeated source restarts, looking for patterns or dependence that are not visible in a single continuous sequence. Restart testing explained →
20. Why are restart datasets different from ordinary sequential data?
They capture repeated initialization behavior. A source may look acceptable during one long run while producing problematic structure immediately after each restart.
Health and conditioning
21. What are RNG health tests?
Health tests are runtime checks intended to detect source failures or unexpected behavior while the entropy source operates. Health tests explained →
22. Are health tests the same as entropy estimation?
No. Health tests detect certain failures during operation; entropy estimation characterizes unpredictability under an evaluation model.
23. Is a hash function automatically a valid conditioner?
Not automatically. The role and assumptions of a conditioning function depend on the architecture and assurance framework. Conditioning explained →
Testing
24. Can NIST STS prove a generator is secure?
No. Output statistical suites can reveal some anomalies, but passing them does not prove the physical entropy model, implementation or operational monitoring is sound. Why statistics are not enough →
25. How should I test an entropy source?
Start with raw data, document the source model and acquisition chain, choose an appropriate IID/non-IID assumption, estimate entropy conservatively, check restart behavior where applicable, and review conditioning and health monitoring. Testing workflow →
26. How do I test a QRNG specifically?
Test the complete path: claimed quantum process, classical measurement chain, source model, raw data, entropy estimate, environmental behavior, health monitoring, conditioning and final integration. QRNG testing guide →
27. Can I run a preliminary assessment locally?
Yes. QRNG.io's local assessment kit is designed to run NIST's assessment tooling on your own machine so raw datasets do not need to leave your environment. Get the local kit →
Standards landscape
28. What is BSI AIS 20/31?
AIS 20/31 is the German BSI framework for evaluating classes of random-number generators. Its terminology and structure differ from NIST's SP 800-90 series. NIST vs AIS 20/31 →
29. Is there QRNG-specific ETSI guidance?
Yes. ETSI published TR 104 171 V1.1.1 in March 2026, a Technical Report focused on practical QRNG implementation guidance. It is not a harmonised standard. ETSI guidance explained →
30. What should I evaluate before integrating QRNG hardware?
Ask where entropy originates, how it is measured and modeled, how much entropy is conservatively credited, how failures are detected, how conditioning works, how the output is integrated, and what evidence supports any compliance or validation claim. If you are evaluating hardware, see the iQrypto evaluation path →.
Sources and further reading
Part of the QRNG.io quantum randomness knowledge hub.