Ahto Buldas


Co-Founder, GuardTime

Professor, Tallinn University of Technology

e-mail: ahto.buldas@ttu.ee

Curriculum Vitae:

(in english) , (in estonian)


  1. Buldas, A.: Digitaalskeemide simuleerimise algebraliste meetodite analüüs. Magistritöö, Tallinna Tehnikaülikool (master thesis, in estonian) (1993) .pdf
  2. Ubar, R., Buldas, A., Paomets, P., Raik, J., Tulit, V.: A PC-based CAD System for Training Digital Test. In: Proc. EUROCHIP Workshop on VLSI Design Training, pp.152--157 (1994)
  3. Buldas, A.: Comparability graphs and the structure of finite graphs. Proc. Estonian Acad. Sci. Phys. Math., 45 (2/3): 117--127 (1996)
  4. Buldas, A., Priisalu, J.: A semi-formal method for security estimation. In: Haav, H.-M., Thalheim, B. (Eds.): Baltic DB\&IS 1996, v.2, pp. 206--212 (1996)
  5. Buldas, A.: Congruence lattice of a graph. Proc. Estonian Acad. Sci. Phys. Math., 46 (3): 155--170 (1997)
  6. Buldas, A., Põldre, J.: A VLSI implementation of RSA and IDEA encryption engine. In: Proc. NORCHIP'97, pp. 281--288 (1997)
  7. Buldas, A., Laud, P., Lipmaa, H., Villemson, J.: Ajatempli protokollid, turvavajadused ja tehnilised nõuded. Lähteuuring DO-LU-X-22-1297, Cybernetica AS. Tellitud Eesti Informaatikakeskuse poolt seoses Eesti digitaalallkirja seaduse loomisega. (1997) .pdf
  8. Buldas, A.: Graphs and lattice varieties. Proc. Estonian Acad. Sci. Phys. Math., 47 (2): 100--109 (1998)
  9. Buldas, A., Laud, P., Lipmaa, H., Villemson, J.: Time-Stamping with binary linking schemes. In: Krawczyk, H. (Ed.): CRYPTO'98. LNCS 1462, pp. 486--501 (1998) .ps, .pdf, 10.1007/BFb0055749
  10. Buldas, A., Laud, P.: New linking schemes for digital time-stamping. In: ICISC'98, pp.3--14, Seoul, Korea (1998) .ps, .pdf,
  11. Buldas, A., Oit, M., Praust, V.: Turvaklasside kirjeldused. Tehniline aruanne DO-X-09-0498. Cybernetica AS, Infotehnoloogia osakond (1998) .pdf
  12. Buldas, A.: An algebraic approach to the structure of graphs. Phd thesis, Tallinn University of Technology (1999) .pdf
  13. Buldas, A., Oit, M., Sarv, M.: (1999). Data security in state registers: theory and practice. In: Proc. Information Technologies and Telecommunications in the Baltic States, pp. 69--72 (1999)
  14. Buldas, A., Lipmaa, H., Schoenmakers, B.: Optimally efficient accountable time-stamping. In: Imai, H., Zheng, Y. (Eds.): PKC 2000. LNCS 1751, pp.293--305 (2000) .ps, .pdf, 10.1007/978-3-540-46588-1_20
  15. Buldas, A., Roos, M., Praust, V., Willemson, J.: On long-term validation of E-documents. Baltic IT-Review, 2 (17): 53--56 (2000)
  16. Buldas, A., Laud, P., Lipmaa, H.: Accountable Certificate Management using undeniable attestations. In: The 7th ACM Conference on Computer and Communication Security -- CCS'00, pp. 9--17 (2000) .ps, .pdf, 10.1145/352600.352604
  17. Ansper, A., Buldas, A., Roos, M., Willemson, J.: Efficient long-term validation of digital signatures. In: Kim, K. (Eds.): PKC'2001. LNCS 1992, pp.402--415 (2001) .ps, .pdf, 10.1007/3-540-44586-2_29
  18. Ansper, A., Buldas, A., Saarepera, M., Willemson, J.: Improving the availability of time-stamping services. In: Varadharajan, V., Mu, Y. (Eds.): ACISP'2001. LNCS 2119, pp.360--375 (2001) .ps, .pdf, 10.1007/3-540-47719-5_29
  19. Ansper, A., Buldas, A., Heiberg, S., Oit, M., Oone, K., Sepp, O.,Villemson, J.: Digitaalallkirja juurutamine riigiasutustes: strateegiline plaan. (Strategic plan for applying digital signatures in state institutions ) November (2001) .pdf
  20. Buldas, A., Laud, P., Lipmaa, H.: Eliminating counterevidence with applications to accountable certificate management. Journal of Computer Security, 10 (3): 273--296 (2002) .pdf
  21. Buldas, A., Roos, M., Willemson, J.: Undeniable replies for database queries. In: Haav, H.-M., Kalja,A. (Eds.): Baltic DB\&IS 2002, v.2, pp.215--226 (2002) CiteSeerX
  22. Buldas, A., Saarepera, M.: Electronic signature system with small number of private keys. In: The 2nd Annual PKI Research Workshop, pp. 96--108 (2003) .pdf
  23. Ansper, A., Buldas, A., Freudenthal, M., Willemson, J.: Scalable and efficient PKI for inter-organizational communication. In: ACSAC'2003, pp. 406--415 (2003) .pdf, 10.1109/CSAC.2003.1254335
  24. Buldas, A., Freudenthal, M.: Long term archiving of electronic signatures. Baltic IT-Review, 1 (28): 69--74 (2003)
  25. Buldas, A., Saarepera, M.: On provably secure time-stamping schemes. In: Lee, P.J. (Ed.): ASIACRYPT 2004. LNCS 3329, pp. 500--514 (2004) .ps, .pdf 10.1007/978-3-540-30539-2_35
  26. Buldas, A., Laud, P., Saarepera, M., Willemson, J.: Universally composable time-stamping schemes with audit. In: Zhou, J., Lopez, J., Deng, R.H., Bao, F. (Eds.): ISC 2005, LNCS 3650, pp. 359--373 (2005) 10.1007/11556992_26
  27. Buldas, A., Laur, S.: Do broken hash functions affect the security of time-stamping schemes? In: Zhou, J., Yung, M., Bao, F. (Eds.): ACNS'06, LNCS 3989, pp. 50--65 (2006) 10.1007/11767480_4
  28. Buldas, A., Laud, P., Priisalu, J., Saarepera, M., Willemson, J.: Rational choice of security measures via multi-parameter attack trees. In: Lopez, J. (Ed.): CRITIS 2006. LNCS 4347, pp. 235--248 (2006) 10.1007/11962977_19
  29. Buldas, A., Laur, S.: Knowledge-binding commitments with applications in time-stamping. In: Okamoto, T., Wang. X. (Eds.): PKC 2007. LNCS 4450, pp. 150--165 (2007) 10.1007/978-3-540-71677-8_11
  30. Buldas, A., Mägi, T.: Practical security analysis of e-voting systems. In: Miyaji, A., Kikuchi, H., Rannenberg, K. (Eds.): IWSEC 2007. LNCS 4752, pp. 320--335 (2007) 10.1007/978-3-540-75651-4_22
  31. Buldas, A., Jürgenson, A.: Does secure time-stamping imply collision-free hash functions? In: Susilo, W., Liu, J.K., Mu, Y. (Eds.): ProvSec 2007. LNCS 4784, pp. 138--150 (2007) 10.1007/978-3-540-75670-5_9
  32. Buldas, A., Niitsoo, M.: Can we construct unbounded time-stamping schemes from collision-free hash functions? In: Baek, J.S., Bao, F., Chen, K., Lai, X. (Eds.): ProvSec 2008. LNCS 5324, pp. 254--267 (2008) 10.1007/978-3-540-88733-1_18
  33. Buldas, A., Jürgenson, A., Niitsoo, M.: Efficiency bounds for adversary constructions in black-box reductions. In: Boyd, C., Gonzalez Nieto, J. (Eds.): ACISP 2009. LNCS 5594, pp.264--275 (2009) 10.1007/978-3-642-02620-1_19
  34. Buldas, A., Laur, S., Niitsoo, M.: Oracle separation in the non-uniform model. In: Pieprzyk, J., Zhang, F. (Eds.): ProvSec 2009. LNCS 5848, pp. 230--244 (2009) 10.1007/978-3-642-04642-1_19
  35. Buldas, A., Niitsoo, M.: Optimally tight security proofs for hash-then-publish time-stamping. In: Steinfeld, R., Hawkes, P. (Eds.): ACISP 2010. LNCS 6168, pp. 318--335 (2010) 10.1007/978-3-642-14081-5_20
  36. Buldas, A., Stepanenko, R.: Upper bounds for adversaries' utility in attack trees. In: Grossklags, J., Walrand, J. (Eds.): GameSec 2012. LNCS 7638, pp. 98--117 (2012) 10.1007/978-3-642-34266-0_6 (.pdf)
  37. Buldas, A., Niitsoo, M.: Black-box separations and their adaptability to the non-uniform model. In: Boyd, C., Simpson, L. (Eds.): ACISP 2013. LNCS 7959, pp. 152--167 (2013) 10.1007/978-3-642-39059-3_11
  38. Buldas, A., Laanoja, R.: Security proofs for hash tree time-stamping using hash functions with small output size. In: Boyd, C., Simpson, L. (Eds.): ACISP 2013, LNCS 7959, pp. 235--250 (2013) 10.107/978-3-642-39059-3_16
  39. Buldas, A., Andres Kroonmaa, Laanoja, R.: Keyless signatures infrastructure: How to build global distributed hash-trees. In: Riis Nielson, H., Gollmann, D. (Eds.): NordSec 2013. LNCS 8208, pp. 313--320 (2013) 10.1007/978-3-642-41488-6_21
  40. Ansper, A., Buldas, A., Freudenthal, M., Willemson, J.: High-performance qualified digital signatures for X-Road. In: Riis Nielson, H., Gollmann, D. (Eds.): NordSec 2013. LNCS 8208, pp. 123--138 (2013) 10.1007/978-3-642-41488-6_9
  41. Ansper, A., Buldas, A., Freudenthal, M., Willemson, J.: Protecting a federated database infrastructure against denial-of-service attacks. In: Luiijf, E., Hartel, P. (Eds.): CRITIS 2013. LNCS 8328, pp. 26--37 (2013) 10.1007/978-3-319-03964-0_3
  42. Buldas, A., Lenin, A.: New efficient utility upper bounds for the fully adaptive model of attack trees. In: Das, S.K., Nita-Rotaru, C., Kantarcioglu, M. (Eds.): GameSec 2013. LNCS 8252, pp. 192--205 (2013) 10.1007/978-3-319-02786-9_12
  43. Buldas, A., Laanoja, R., Laud, P., Truu, A.: Bounded pre-image awareness and the security of hash-tree keyless signatures. In: Chow, S.S.M., Liu, J.K., Hui, L.C.K., Yiu, S.M. (Eds.): Provsec 2014. LNCS 8782, pp. 130--145 (2014) 10.1007/978-3-319-12475-9_10
  44. Buldas, A., Lenin, A.: Limiting adversarial budget in quantitative security analysis. In: Poovendran, R., Saad, W. (Eds.): GameSec 2014. LNCS 8840, pp. 153--172 (2014) 10.1007/978-3-319-12601-2_9
  45. Buldas, A., Truu, A., Laanoja, R., Gerhards, R.: Efficient record-level keyless signatures for audit logs. In: Bernsmed, K., Fisher-Hübner, S. (Eds.): NordSec 2014. LNCS 8788, pp. 149--164 (2014) 10.1007/978-3-319-11599-3_9
  46. Buldas, A., Heero, K., Laud, P., Talviste, R., Willemson, J.: Cryptographic algorithms lifecycle report 2016. Information System Authority. Doc. A-101-3. June 22 (2016)
  47. Buldas, A., Laanoja, R., Truu, A.: Keyless signature infrastructure and PKI: hash-tree signatures in pre- and post-quantum world. International Journal of Services Technology and Management (IJSTM), 23 (1/2) (2017) 10.1504/IJSTM.2017.10002708"
  48. Buldas, A., Saarepera, M.: Are the current system engineering practices sufficient to meet cyber crime? In: Tryfonas, T. (Ed.): HAS 2017. LNCS 10292, pp. 451--463 (2017) 10/007/978-3-319-58460-7_31
  49. Buldas, A., Geihs, M., Buchmann, J.: Long-term secure commitments via extractable-binding commitments. In: Pieprzyk, J., Suriadi, S. (Eds.): ACISP 2017. LNCS 10343, pp. 65--81 (2017) 10.1007/978-3-319-60055-0_4
  50. Buldas, A., Kalu, A., Laud, P., Oruaas, M.: Server-supported RSA signatures for mobile devices. Foley, S.N., Gollmann, D., Snekkenes, E. (Eds.): ESORICS 2017, Part I. LNCS 10492, pp. 1--19 (2017) 10.1007/978-3-319-66402-6_19
  51. Buldas, A., Lenin, A., Willemson, J., Charnamord, A.: Simple infeasibility certificates for attack trees. In: Obana, S., Chida, K. (Eds.): IWSEC 2017. LNCS 10418, pp. 39--55 (2017) 10.1007/978-3-319-64200-0_3
  52. Buldas, A., Geihs, M., Buchmann, J.: Long-term secure time-stamping using preimage-aware hash functions. In: Okamoto, T., Yu, Y., Au, M.H., Li, Y. (Eds.): ProvSec 2017. LNCS 10592, pp. 251--260 (2017) 10.1007/978-3-319-68637-0_15 Extended version: Cryptology ePrint Archive 2017/754: (.pdf)
  53. Buldas, A., Laanoja, R., Truu, A.: A server-assisted hash-based signature scheme. In: Lipmaa, H., Mitrokotsa, A., Matulevičius, R. (Eds.): NordSec 2017. LNCS 10674, pp. 3--17 (2017) 10.1007/978-3-319-70290-2_1

Ph.D. Theses Supervised

  1. Jan Villemson: Size-efficient interval time stamps. Ph.D. thesis. Ahto Buldas (Sup.), University of Tartu (2002) .pdf
  2. Aivo Kalu: Efficient semantics of parallel and serial models of attack trees. Ph.D. thesis. Ahto Buldas, Jan Villemson (Sup.), Tallinn University of Technology (2010) .pdf
  3. Rain Ottis: A systematic approach to offensive volunteer cyber militia. Ph.D. thesis. Ahto Buldas, Peeter Lorents (Sup.), Tallinn University of Technology (2011) .pdf
  4. Margus Niitsoo: Black-box oracle separation techniques with applications in time-stamping. Ph.D. thesis. Ahto Buldas (Sup.), University of Tartu (2011) .pdf
  5. Aleksandr Lenin: Reliable and efficient determination of the likelihood of rational attacks. Ph.D. thesis. Ahto Buldas (Sup.), Tallinn University of Technology (2016) .pdf

Lecture Notes

IDS0010 Sissejuhatus andmeturbesse

ITX8110 Introduction to Combinatorics and Cryptography

Complexity Theory (Univ. of Tartu)

Combinatorics (Univ. of Tartu)

Sissejuhatus krüptograafiasse

Hulgateooria (Set Theory), Spring 1994 (.pdf)

Sissejuhatus Galois' teooriasse (Introduction to the Galois' Theory, 1993, seminar notes)

Students' Seminar Slides

Seminar for Cyber Defence Students, Autumn 2011

Seminar for Cyber Defence Students, Autumn 2012

Popular Science Publications (in estonian)

  1. Buldas, A.: Krüptoloogia. Miks ja kuidas? Arvutimaailm, 3: 14--15 (1994)
  2. Buldas, A., Lakspere, E., Priisalu, J.: Mikroarvuti plastkaardis. Arvutimaailm, 4: 51--53 (1994)
  3. Buldas, A.: Algoritmid ja diagonaalsed tõestused. Arvutustehnika ja andmetöötlus, 1: 5--10 (1995) .ps
  4. Buldas, A.: Graafid ja järjestused. Arvutustehnika ja andmetöötlus, 2: 2--8 (1995) .ps
  5. Buldas, A.: Sissejuhatus matroidide teooriasse. Arvutustehnika ja andmetöötlus, 3: 2--5 (1995) .ps
  6. Buldas, A.: Goodsteini teoreemist. Arvutustehnika ja andmetöötlus, 4: 2--6 (1995) .ps
  7. Buldas, A.: Mis on p-aadilised arvud? Arvutustehnika ja andmetöötlus, 9: 2--8 (1995) .ps
  8. Buldas, A.: Elektrondokumendid tõendusmaterjalina. Arvutimaailm, 8: 23--25 (1997)
  9. Buldas, A., Lipmaa, H.: Ajatemplid digitaaldokumentidel. Arvutimaailm, 2: 45--47 (1998)
  10. Buldas, A.: Allkirjad elektroonilistel dokumentidel: vääramatu tõenduse algoritmidest. Arvutustehnika ja andmetöötlus, 6: 36--40 (2000)
  11. Buldas, A.: Teadusest, ärist ja impeeriumi pärandusest. Arvutustehnika ja andmetöötlus, 4: 5--8 (2001)

Selected Seminar Presentations

  1. Arvud ja mängud (Numbers and games), TPedI matemaatikaseminar (1995) .ps
  2. Graafi modulaardekompositsioon (Modular decomposition of a graph) Leo Võhandu seminar (1995) .ps