New High Entropy Element for FPGA Based True Random Number Generators

  • Michal Varchola
  • Milos Drutarovsky
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6225)


We demonstrate a new high-entropy digital element suitable for True Random Number Generators (TRNGs) embedded in Field Programmable Gate Arrays (FPGAs). The original idea behind this principle lies in the randomness extraction on oscillatory trajectory when a bi-stable circuit is resolving a metastable event. Although such phenomenon is well known in the field of synchronization flip-flops, this feature has not been applied for TRNG designs. We propose a new bi-stable structure – Transition Effect Ring Oscillator (TERO) where oscillatory phase can be forced on demand and be reliably synthesized in FPGA. Randomness is represented as a variance of the TERO oscillations number counted after each excitation. Variance is highly dependent on the internal noise of logic cells and can be used easily for reliable instant inner testing of each generated bit. Our proposed mathematical model, simulations and hardware experiments show that TERO is significantly more sensitive to intrinsic noise in FPGA logic cells and less sensitive to global perturbations than a ring oscillator composed from the same elements. The experimental TERO-based TRNG passes NIST 800-22 tests.


TRNG oscillatory metastability randomness extraction inner testability 


  1. 1.
    Bochard, N., Bernard, F., Fischer, V.: Observing the randomness in RO-based TRNG. In: International Conference on Reconfigurable Computing and FPGAs, Cancun, Quintana Roo, Mexico, December 9-11, pp. 237–242. IEEE Computer Society, Los Alamitos (2009)CrossRefGoogle Scholar
  2. 2.
    Bucci, M., Giancane, L., Luzzi, R., Varanonuovo, M., Trifilett, A.: A Novel Concept for Stateless Random Bit Generators in Cryptographic Applications. In: 2006 IEEE International Symposium of Circuits and Systems - ISCAS 2006, Island of Kos, Greece, May 21-24, pp. 317–320. IEEE Computer Society, Los Alamitos (2006)Google Scholar
  3. 3.
    Dichtl, M., Golić, J.: High-Speed True Number Generation with Logic Gates Only. In: Paillier, P., Verbauwhede, I. (eds.) CHES 2007. LNCS, vol. 4727, pp. 45–62. Springer, Heidelberg (2007)CrossRefGoogle Scholar
  4. 4.
    Dichtl, M., Meyer, B., Seuschek, H.: SPICE Simulation of a “Provably Secure” True Random Number Generator (2008),
  5. 5.
    Epstein, M., Hars, L., Krasinski, R., Rosner, M., Zheng, H.: Design and Implementation of a True Random Number Generator Based on Digital Circuit Artifacts. In: Walter, C.D., Koç, Ç.K., Paar, C. (eds.) CHES 2003. LNCS, vol. 2779, pp. 152–165. Springer, Heidelberg (2003)CrossRefGoogle Scholar
  6. 6.
    Fischer, V., Drutarovsky, M.: True Random Number Generator Embedded in Reconfigurable Hardware. In: Kaliski Jr., B.S., Koç, Ç.K., Paar, C. (eds.) CHES 2002. LNCS, vol. 2523, pp. 415–430. Springer, Heidelberg (2003)CrossRefGoogle Scholar
  7. 7.
    Golic, J.: New Methods for Digital Generation and Postprocessing of Random Data. IEEE Transactions on Computers 55(10), 1217–1229 (2006)CrossRefGoogle Scholar
  8. 8.
    Kacprzak, T.: Analysis of Oscillatory Metastable Operation of an R-S Flip-Flop. IEEE Journal of Solid-State Circuits 23(1), 260–266 (1988)CrossRefGoogle Scholar
  9. 9.
    Koç, Ç.K. (ed.): Cryptographic Engineering. Springer, Heidelberg (2009)Google Scholar
  10. 10.
    Killmann, W., Schindler, W.: Functionality classes and evaluation methodology for true (physical) random number generators, Version 3.1 (September 2001),
  11. 11.
    Linear Technology: LT Spice IV,
  12. 12.
    Markettos, A.T., Moore, S.W.: The Frequency Injection Attack on Ring-Oscillator-Based True Random Number Generators. In: Clavier, C., Gaj, K. (eds.) CHES 2009. LNCS, vol. 5747, pp. 317–331. Springer, Heidelberg (2009)CrossRefGoogle Scholar
  13. 13.
    Menezes, J., Oorschot, P., Vanstone, S.: Handbook of Applied Cryptography. CRC Press, New York (1997), zbMATHGoogle Scholar
  14. 14.
    Rabaey, J.M., Chandrakasan, A., Nilolic, B.: Digital Integrated Circuits, 2nd edn. Prentice-Hall, Englewood Cliffs (February 2010), Google Scholar
  15. 15.
    Reyneri, L., Corso, D., Sacco, B.: Oscillatory Metastability in Homogenous and Inhomogeneous Flip-Flops. IEEE Journal of Solid-State Circuits 25(1), 254–264 (1990)CrossRefGoogle Scholar
  16. 16.
    Rukhin, A., Soto, J., Nechvatal, J., Smid, M., Barker, E., Leigh, S., Levenson, M., Vangel, M., Banks, D., Heckert, A., Dray, J., Vo, S.: A Statistical Test Suite For Random And Pseudorandom Number Generators For Cryptographic Applications, NIST Special Publication 800-22 rev1a (April 2010),
  17. 17.
    Schellekens, D., Preneel, B., Verbauwhede, I.: FPGA Vendor Agnostic True Random Number Generator. In: Proceedings of the 16th International Conference on Field Programmable Logic and Applications (FPL), Madrid, Spain, August 28-30, pp. 1–6. IEEE Computer Society, Los Alamitos (2006)CrossRefGoogle Scholar
  18. 18.
    Schindler, W., Killmann, W.: Evaluation Criteria for True (Physical) Random Number Generators Used in Cryptographic Applications. In: Kaliski Jr., B.S., Koç, Ç.K., Paar, C. (eds.) CHES 2002. LNCS, vol. 2523, pp. 431–449. Springer, Heidelberg (2003)CrossRefGoogle Scholar
  19. 19.
    Sunar, B.: Response to Dichtl’s Criticism (March 2008),
  20. 20.
    Sunar, B., Martin, W.J., Stinson, D.R.: A Provably Secure True Random Number Generator with Built-in Tolerance to Active Attacks. IEEE Transactions on Computers 56(1), 109–119 (2007)CrossRefMathSciNetGoogle Scholar
  21. 21.
    Tokunaga, C., Blaauw, D., Mudge, T.: True Random Number Generator With a Metastability-Based Quality Control. IEEE Journal of Solid-State Circuits, 78–85 (January 2008)Google Scholar
  22. 22.
    Vasyltsov, I., Hambardzumyan, E., Kim, Y.S., Karpinskyy, B.: Fast Digital TRNG Based on Metastable Ring Oscillator. In: Oswald, E., Rohatgi, P. (eds.) CHES 2008. LNCS, vol. 5154, pp. 164–180. Springer, Heidelberg (2008)CrossRefGoogle Scholar
  23. 23.
    Wold, K., Tan, C.H.: Analysis and Enhancement of Random Number Generator in FPGA Based on Oscillator Rings. International Journal of Reconfigurable Computing 2009, 1–8 (June 2009),
  24. 24.
    Wollinger, T., Guajardo, J., Paar, C.: Security on FPGAs: State-of-the-art implementations and attacks. ACM Transactions on Embedded Computing Systems (TECS), 534–574 (2004)Google Scholar
  25. 25.

Copyright information

© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Michal Varchola
    • 1
  • Milos Drutarovsky
    • 1
  1. 1.Department of Electronics and Multimedia CommunicationsTechnical University of KosiceKosiceSlovak Republic

Personalised recommendations