Ahto Buldas Chief researcher, Cybernetica AS Professor, Tallinn University of Technology Professor, University of Tartu

phone: +3726654241
e-mail: ahto.buldas@ut.ee

Curriculum Vitae:

Selected Publications

1. Ahto Buldas. Congruence lattice of a graph. Proc. Estonian Acad. Sci. Phys. Math., 1997, 46, 3, 155-170.
2. Ahto Buldas and Jüri Põldre. A VLSI implementation of RSA and IDEA encryption engine. In NORCHIP'97, Tallinn 1997.
3. Ahto Buldas, Peeter Laud, Helger Lipmaa, Jan Villemson, "Ajatempli protokollid, turvavajadused ja tehnilised nõuded," Technical Report DO-LU-X-22-1297, Cybernetica, 1997, 46 pages ["Timestamp protocols, security needs and technical requirements". Funded by Estonian Informatics Centre]
4. Ahto Buldas. Graphs and lattice varieties. Proc. Estonian Acad. Sci. Phys. Math., 1998, 47, 2, 100-109.
5. Ahto Buldas, Peeter Laud, Helger Lipmaa and Jan Villemson. Time-Stamping with binary linking schemes. In Advances in Cryptology - CRYPTO'98, LNCS 1462, 486-501. Springer-Verlag, 1998. .ps, .pdf
6. Ahto Buldas and Peeter Laud. New linking schemes for digital time-stamping. In Proceedings of The 1st International Conference on Information Security and Cryptology - ICISC'98, 3-14, Seoul, Korea, 1998. .ps, .pdf
7. Ahto Buldas, Helger Lipmaa and Berry Schoenmakers. Optimally efficient accountable time-stamping. In Public Key Cryptography - PKC'2000, Melbourne, Australia. LNCS 1751, 293-305. Springer-Verlag, 2000. .ps, .pdf
8. Ahto Buldas, Meelis Roos, Valdo Praust and Jan Willemson. On long-term validation of E-documents. Baltic IT-Review, 2 (17): 53-56, 2000.
9. Ahto Buldas, Peeter Laud and Helger Lipmaa. Accountable Certificate Management using undeniable attestations. In The 7th ACM Conference on Computer and Communication Security - CCS'00, Athens, Greece. Nov. 1-4, 2000. .ps, .pdf
10. Arne Ansper, Ahto Buldas, Meelis Roos and Jan Willemson. Efficient long-term validation of digital signatures. In Public Key Cryptography - PKC'2001, Cheju Island, Korea. Feb. 13-15, 2001. LNCS 1992, 402-415. Springer-Verlag, 2001. .ps, .pdf
11. Arne Ansper, Ahto Buldas, Märt Saarepera and Jan Willemson. Improving the availability of time-stamping services. In The 6th Australasian Conference on Information Security and Privacy - ACISP'2001, Sydney, Australia, July 2-4, 2001. LNCS 2119, 360-375. Springer-Verlag, 2001. .ps, .pdf
12. Ahto Buldas, Peeter Laud, Helger Lipmaa. Eliminating counterevidence with applications to accountable certificate management. Journal of Computer Security, v. 10, n. 3, pp. 273-296, 2002.
13. A.Buldas, M.Roos, J.Willemson. Undeniable replies for database queries. In H.-M. Haav, A.Kalja, eds., Proc. of the 5th International Baltic Conference On Databases and Information Systems -- Baltic DB\&IS 2002, v.2, pp.215-226. Institute of Cybernetics, Tallinn, 2002.
14. Ahto Buldas, Märt Saarepera. Electronic signature system with small number of private keys. In 2nd Annual PKI Research Workshop, pp.96-108. NIST Gaithersburg MD, USA. April 28-29, 2003.
15. Arne Ansper, Ahto Buldas, Margus Freudenthal, Jan Willemson. Scalable and Efficient PKI for Inter-Organizational Communication. Annual Computer Security Applications Conference -- ACSAC'2003.
16. Ahto Buldas and Märt Saarepera. On provably secure time-stamping schemes. In ASIACRYPT 2004, LNCS 3329, pp. 500--514. 2004. .ps, .pdf
17. Ahto Buldas, Peeter Laud, Märt Saarepera, Jan Willemson. Universally composable time-stamping schemes with audit. In Information Security Conference -- ISC 2005, LNCS 3650, pp.359--373. 2005.
18. Ahto Buldas, Sven Laur. Do broken hash functions affect the security of time-stamping schemes? In 4th International Conference on Applied Cryptography and Network Security -- ACNS'06, LNCS 3989, pp. 50-65, 2006.
19. Ahto Buldas, Peeter Laud, Jaan Priisalu, Märt Saarepera, and Jan Willemson. Rational Choice of Security Measures via Multi-Parameter Attack Trees. In Critical Information Infrasturctured Security First International Workshop -- CRITIS 2006, LNCS 4347, pp. 235-248, 2006.
20. Ahto Buldas, Sven Laur. Knowledge-binding commitments with applications in time-stamping. In The International Conference on Theory and Practice of Public-Key Cryptography (PKC 2007). Beijin, China, April 16-20, 2007. LNCS 4450, pp. 150-165, 2007.
21. Ahto Buldas, Triinu Mägi. Practical security analysis of e-voting systems. In the Second International Workshop on Security (IWSEC) 2007. Nara, Japan, October 29-31, 2007. LNCS 4752, pp.320-335, 2007.
22. Ahto Buldas, Aivo Jürgenson. Does secure time-stamping imply collision-free hash functions? In the 1st International Conference on Provable Security (ProvSec) 2007. Wollongong, Australia, October 31-November 2, 2007. LNCS 4784, pp.138-150, 2007.
23. Ahto Buldas, Margus Niitsoo. Can we construct unbounded time-stamping schemes from collision-free hash functions? In the 2nd International Conference on Provable Security (ProvSec) 2008. Shanghai, China, October 30-November 1, 2008. LNCS 5324, pp.254-267, 2008.
24. Ahto Buldas, Aivo Jürgenson, Margus Niitsoo. Efficiency bounds for adversary constructions in black-box reductions. In C. Boyd and J. Gonz.alez Nieto (Eds.): ACISP 2009, LNCS 5594, pp.264-275, 2009.
25. Ahto Buldas, Sven Laur, Margus Niitsoo. Oracle separation in the non-uniform model. In J.Pieprzyk and F.Zhang (Eds.): the 3rd International Conference on Provable Security (ProvSec) 2009, November 11-13, 2009, Guangzhou, China. LNCS 5848, pp. 230-244, 2009.
26. Buldas, A., Niitsoo, M.: Optimally tight security proofs for hash-then-publish time-stamping. In: Steinfeld, R., Hawkes, P. (eds.) ACISP 2010. LNCS, vol. 6168, pp. 318.335. (2010) (to appear)

Chapters in Books

1. Vello Hanson, Ahto Buldas, Tarvi Martens, Helger Lipmaa, Arne Ansper, Viljar Tulit, "Infosüsteemide turve I. Turvarisk" Küberneetika AS, 1997, 125 pages ["Security of Information Systems I.", book, in Estonian]
2. Vello Hanson, Ahto Buldas, Tarvi Martens, Helger Lipmaa, Arne Ansper, Viljar Tulit, "Infosüsteemide turve II. Turbetehnoloogia" Küberneetika AS, 1998, 372 pages ["Security of Information Systems II", book, in Estonian]

Selected Popular Math Stories

• Arvud ja mängud (ettekantud TPedI seminaris, 1995)
• Goodsteini teoreemist (avaldatud A&A)
• Graafid ja järjestused (avaldatud A&A)
• Sissejuhatus matroidide teooriasse (avaldatud A&A)
• Graafi modulaardekompositsioon (Leo Võhandu seminari ettekanne)
• Mis on p-aadilised arvud? (avaldatud A&A)
• Algoritmid ja diagonaalsed tõestused (avaldatud A&A)

Lecture Notes

Complexity Theory (University of Tartu)

• Textbook: The lectures are based on the following upcoming textbook: Sanjeev Aurora and Boaz Barak. Complexity Theory: A Modern Approach. http://www.cs.princeton.edu/theory/complexity/
• Lectures in 2009:
  1. Sep 3 (16.15, 404), Introduction (.pdf)
  2. Sep 10 (16.15, 404), Sep 11 (8.15, 405) Computational model and efficient computations (.pdf)
  3. Sep 24 (16.15, 404), Sep 25 (8.15, 405) NP and NP completeness (.pdf)
  4. Oct 1 (16.15, 404) Practicing
  5. Oct 8 (16.15, 404), Oct 9 (8.15, 405) Diagonalization (.pdf)
  6. Oct 15 (16.15, 404) Practicing
  7. Oct 29 (16.15, 404), Oct 30 (8.15, 405) Space complexity (.pdf)
  8. Nov 6 (8.15, 405) Polynomial hierarchy (.pdf)
  9. Nov 19 (16.15, 404) Circuits (.pdf)
  10. Dec 3 (16.15, 404) Randomized computation (.pdf)
  11. Dec 4 (8.15, 405) Interactive proofs (not finished yet!) (.pdf)
  12. Dec 10 (16.15, 404) Practicing
  13. Dec 17 (16.15, 404) Written test
• From previous years:
  1. Year 2007 First test (problems and solutions): .pdf