Podpisi brez možnosti zanikanja

BRECELJ, BOR (author), Jurišić, Aleksandar (mentor)

V nekaterih situacijah ni zaželjeno, da lahko kdorkoli preveri veljavnost digitalnega podpisa. Podpisi brez možnosti zanikanja to dosežejo tako, da mora pri preverjanju podpisa sodelovati tudi podpisnik. Za preverjanje podpisa potrebujemo potrditveni protokol, s katerim dokažemo veljavnost našega podpisa, in zavrnitveni protokol, s katerim lahko dokažemo, da podpis ni naš. Poleg varnostne zahteve, da nihče ne more ponarediti podpisa, moramo dodati še zahtevo, da iz podpisa ni mogoče ugotoviti njegove veljavnosti brez sodelovanja podpisnika. Za oba protokola mora veljati, da sta dokaza brez razkritja znanja. Predstavili bomo vse te varnostne zahteve in navedli dva primera shem za podpis brez možnosti zanikanja skupaj z dokazi varnostnih zahtev.

• Language: Slovenian
• Keywords: digitalni podpisi, kriptografija, podpisi brez možnosti zanikanja
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FRI - Faculty of Computer and Information Science ; FMF - Faculty of Mathematics and Physics
• Year: 2020
• PID: 20.500.12556/RUL-120373
• COBISS.SI-ID: 32203011
• Publication date in RUL: 18.09.2020

BRECELJ, BOR, 2020, Podpisi brez možnosti zanikanja [online]. Bachelor’s thesis. [Accessed 1 April 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=120373

Secondary language

• Language: English
• Title: Undeniable signatures

Abstract

While anybody can verify usual digital signatures, in some cases the signer wants the power to decide who can check his signature. It is the role of undeniable signatures to make this possible. The signer can prove the validity of his signature by using a so called confirmation protocol. However, there is also a need for a (disavowal) protocol the signer uses to deny his authorship of a particular signature. There are two main security requirements for undeniable signatures: first, nobody can forge a signature and, second, this signature must be indistinguishable from a randomly chosen one. Therefore, nobody can verify a signature without the signer's cooperation. For security reasons it is also important that both protocols are zero-knowledge proofs. In this thesis we present security requirements and provide two examples of an undeniable signature scheme. Finally, we give proofs of unforgeability and invisibility.

• Keywords: digital signatures, cryptography, undeniable signatures