Time-Stamping Project Cuculus

Time-stamping research trail in Küberneetika AS (Tallinn, Estonia) started in late 1997 by the order of Estonian Informatics Centre, to work out the missing technological solutions for the upcoming Estonian Law of Digital Signatures. The project started with trying to make the existing time-stamping systems more efficient, and if possible, more secure. Later, since time-stamping by is insufficient to solve all the problems, the research topic was broadened to cover other themes connected with long-term repudiation of digital documents.

This page is complemented by The Cuculus time-stamping service (corporate page by Küberneetika AS, my ex-employer). The current page consists mainly of an up-to-date list of publications.

Mailing List

Involved persons

References

NB! If you are interested in this topic, and doing research in similar areas, I'd welcome you to contact me! My address is helger(at)tcs.hut.fi

1. 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". Written by the order of Estonian Informatics Centre for the work of committee preparing the legal use of electronic documents. In Estonian]
2. Ahto Buldas, Helger Lipmaa, "Digital Signatures, Timestamps and the corresponding Infrastructure", Küberneetika AS, Technical Report 1998-21, [ ps and dvi], Jan 1998, 7 pages
3. Ahto Buldas, Helger Lipmaa, "Ajatemplid digitaaldokumentidel", Arvutimaailm 2/98, pp 45-47 ["Time-stamps on the digital documents", a technical survey. In Estonian]
4. Ahto Buldas, Peeter Laud, Helger Lipmaa, Jan Villemson, Time-Stamping with Binary Linking Schemes." (Advances in Cryptology --- CRYPTO '98; LNCS 1462), pp 486-501)
5. Ahto Buldas and Peeter Laud. New linking schemes for digital time-stamping. In The 1st International Conference on Information Security and Cryptology, pages 3--14, Seoul, Korea, 18--19 December 1998. Korea Institute of Information Security and Cryptology.
6. Helger Lipmaa, "Secure and Efficient Time-Stamping Systems". PhD thesis, University of Tartu, 1999.
7. Meelis Roos, "Integrating Time-Stamping and Notarization". Master thesis, University of Tartu, 1999.
8. Helger Lipmaa, "Digital Signatures and Authentication" (a non-technical survey)
9. Arne Ansper, Ahto Buldas, Jan Willemson, General linking schemes for digitial time-stamping, Technical Report, August 1999, 17 pages.
10. Ahto Buldas, Helger Lipmaa, Berry Schoenmakers, "Optimally Efficient Accountable Time-Stamping". In Yuliang Zheng and Hideki Imai, editors, Public Key Cryptography '2000, volume 1751 of Lecture Notes in Computer Science, pages 293-305, Melbourne, Australia, 18--20 January 2000. Springer Verlag.
11. Ahto Buldas, Valdo Praust, Meelis Roos, Jan Willemson, On Long-Term Validation of E-Documents, International Conference "Information Technologies and Telecommunications in the Baltic States - Baltic IT&T '2000", April 6-7, Radisson SAS Daugava Hotel, Riga, Latvia.
12. Ahto Buldas, Peeter Laud, and Helger Lipmaa. Accountable Certificate Management using Undeniable Attestations. In Sushil Jajodia and Pierangela Samarati, editors, 7th ACM Conference on Computer and Communications Security, pages 9--18, Athens, Greece, 1--4 November 2000. ACM Press. ACM ISBN 1-58113-203-4.
13. Arne Ansper, Ahto Buldas, Meelis Roos, Jan Willemson, Efficient long-term validation of digital signatures, PKC 2001, February 2001, Cheju Island, Korea.
14. Arne Ansper, Ahto Buldas, Märt Saarepera, and Jan Willemson. Improving the Availability of Time-stamping Services. In Vijay Varadharajan and Yi Mu, editors, The 6th Australasian Conference on Information Security and Privacy, volume 2119 of Lecture Notes in Computer Science, pages 360--375, Sydney, Australia, 11--13 July 2001. Springer-Verlag. ISBN 3-540-42300-1.
15. Ahto Buldas, Meelis Roos, Jan Willemson, Undeniable replies for database queries, Fifth International Baltic Conference on DB and IS, June 2002, Tallinn, Estonia 01.11.02
16. Jan Willemson, Size-efficient interval time stamps, PhD thesis, Tartu 2002.
17. Ahto Buldas, Peeter Laud, and Helger Lipmaa. Eliminating Counterevidence with Applications to Accountable Certificate Management. Invited and accepted to Journal of Computer Security. (Supersedes [BLL00]. More publication details to be announced.)
18. Helger Lipmaa. On Optimal Hash Tree Traversal for Interval Time-Stamping. In Agnes Chan and Virgil Gligor, editors, Information Security Conference 2002, volume 2433 of Lecture Notes in Computer Science, pages 357--371, São Paulo, Brazil, 30 September --- 2 October 2002. Springer. 01.11.02
19. Ahto Buldas, Meelis Roos, Jan Willemson, Undeniable replies for database queries, Fifth International Baltic Conference on DB and IS, June 2002, Tallinn, Estonia 01.11.02 (A journal version of this paper)
20. Ahto Buldas, Märt Saarepera, Electronic Signature System with Small Number of Private Keys. In proceedings of the 2nd Annual PKI Research Workshop, 2003.

Some standard drafts etc that base on our work:

• ISO/IEC JTC 1/SC 27N 2597: Information technology - Security techniques - Time stamping services - Part 3: Mechanisms producing linked tokens (Working draft)
• ISO/IEC JTC 1/SC 27N 2719: Information technology - Security techniques - Time stamping services - Part 3: Mechanisms producing linked tokens (Working draft) [supercedes the previous one]

A survey based on our work was completed by Chiara Bulgarelli (in Italian!). Another survey was done by Jean Marc Dieu. And a thesis on time-stamping was written by Mitja Dec^man in Slovenian. Another seminar work in German is available from here: Temporale Authentifikation und Zeitstempeldienste.

Time-Stamping Links

Influence in Estonia

Since our work was initiated to support Estonian Digital Signature Law then obviously it has the largest impact in Estonia. A few theses in Estonian are at least partially based on our work:

• "On Evidential Value of Digital Signatures" (MSc thesis, Tarvi Martens.
• Digitaalsertifikaatide ajutise peatamise tehniline teostatavus (Diploma thesis, Risto Laanoja, 2000)
• Personal Security Environments, (MSc thesis, Margus Freudenthal, 2001)

A few popular overviews in Estonian:

• Kuidas digitaalallkirja allkirjastamine reaalselt toimub? Praktilisi näiteid tarkvara baasil ([How to sign a digital signature in the real life? Practical examples based on software.] Tanel Tammet (IT Meedia, PhD), slides, The seminar of "Äripäev" (the only Estonian business newspaper. Like the FT...)

A few technical overviews in Estonian:

• Ajatempliteenuse protokollid ja andmevormingud ([The protocols and data formats of a time-stamping service], Cybernetica AS)

Other essential links

• Elektrondokumendi seadusandluse komisjon (in Estonian)
• Seletuskiri digitaalallkirja seaduseelnõu juurde (in Estonian)
• Estonian Digital Signature Law is in force now (translation to English, .rtf). Notice the Chapter IV, ``Time-stamping Services and Time-stamping Service Providers''
• The Cuculus time-stamping service (the corporate page by Küberneetika AS)