#### Filter Results:

- Full text PDF available (42)

#### Publication Year

1994

2017

- This year (8)
- Last 5 years (20)
- Last 10 years (25)

#### Publication Type

#### Co-author

#### Journals and Conferences

Learn More

- Ahto Buldas, Peeter Laud, Helger Lipmaa
- IACR Cryptology ePrint Archive
- 2000

This paper initiates a study of accountable certificate management methods, necessary to support long-term authenticity of digital documents. Our main contribution is a model for accountable certificate management, where clients receive attestations confirming inclusion/removal of their certificates from the database of valid certificates. We explain whyâ€¦ (More)

- Ahto Buldas, Peeter Laud, Jaan Priisalu, MÃ¤rt Saarepera, Jan Willemson
- CRITIS
- 2006

We present a simple risk-analysis based method for studying the security of institutions against rational (gain-oriented) attacks. Our method uses a certain refined form of attack-trees that are used to estimate the cost and the success probability of attacks. We use elementary game theory to decide whether the system under protection is a realistic targetâ€¦ (More)

- Ahto Buldas, Peeter Laud, Helger Lipmaa
- Journal of Computer Security
- 2002

This paper presents a method to increase the accountability of certificate management by making it intractable for the certification authority (CA) to create contradictory statements about the validity of a certificate. The core of the method is a new primitive, undeniable attester, that allows someone to commit to some set S of bitstrings by publishing aâ€¦ (More)

- Ahto Buldas, Peeter Laud, Helger Lipmaa, Jan Willemson
- CRYPTO
- 1998

We state the basic requirements for time-stamping systems applicable as the necessary support to the legal use of electronic documents. We analyze the main drawbacks of the time-stamping systems proposed to date and present a new system that meets all the stated requirements. We prove that these requirements cannot be signi cantly tightened.

- Arne Ansper, Ahto Buldas, MÃ¤rt Saarepera, Jan Willemson
- ACISP
- 2001

We discuss the availability questions that arise when digital time stamps are used for preserving the evidentiary value of electronic documents. We analyze the time-stamping protocols known to date and point out some weaknesses that have not been addressed so far in scienti c literature. Without addressing and solving them, any advantage of theâ€¦ (More)

- Ahto Buldas, Roman Stepanenko
- GameSec
- 2012

Attack trees model the decision making process of an adversary who plans to attack a certain system. Attack-trees help to visualize possible attacks as Boolean combinations of atomic attacks and to compute attack-related parameters such as cost, success probability and likelihood. The known methods of estimating adversarieâ€™s utility are of high complexityâ€¦ (More)

- Ahto Buldas, Helger Lipmaa, Berry Schoenmakers
- Public Key Cryptography
- 2000

Efficient secure time-stamping schemes employ a 2-level approach in which the time-stamping service operates in rounds. We say that a time-stamping service is accountable if if it makes the TSA and other authorities accountable for their actions by enabling a principal to detect and later prove to a judge any frauds, including attempts to reorderâ€¦ (More)

- Ahto Buldas, Peeter Laud, MÃ¤rt Saarepera, Jan Willemson
- ISC
- 2005

We present a Universally Composable (UC) time-stamping scheme based on universal one-way hash functions. The model we use contains an ideal auditing functionality, the task of which is to check that the roundsâ€™ digests are correctly computed. Our scheme uses hash-trees and is just a slight modification of the known schemes of Haber-Stornetta and Benaloh-deâ€¦ (More)

- Ahto Buldas, Sven Laur
- 2007

We prove in a non-black-box way that every bounded list and set commitment scheme is knowledge-binding. This is a new and rather strong security condition, which makes the security definitions for time-stamping much more natural compared to the previous definitions, which assume unpredictability of adversaries. As a direct consequence, list and setâ€¦ (More)

- Meelis Roos, Ahto Buldas, Jan Willemson
- BalticDB&IS
- 2002