2022-02.html.j2 (2806B)
1 {% extends "common/news.j2" %} 2 {% block body_content %} 3 <h1>2022-2: Adding Schnorr's Blind Signatures to Taler</h1> 4 <p> 5 Gian Demarmels and Lucien Heuzeveldt have finished their 6 <a href="/papers/cs-thesis.pdf">Bachelor's thesis</a> 7 which adds a second blind signature scheme to GNU Taler. 8 </p> 9 <h2>Introduction video</h2> 10 <p> 11 <video id="video" poster="/images/logo-2021.svg" autobuffer="" height="360" width="640" controls="controls"> 12 <source src="/videos/cs-movie.mp4" type="video/mp4" \> 13 </video> 14 </p> 15 <h2>Abstract</h2> 16 <p> 17 The goal of this thesis is to improve Taler’s performance and provide cipher agility by 18 adding support for Schnorr’s blind signatures. To achieve this goal, the current state in 19 research for Schnorr signatures needs to be analyzed. After choosing a signature scheme, 20 it has to be integrated into the Taler protocols. Besides implementing the redesigned 21 protocols in Taler, an implementation of the cryptographic routines is needed. 22 The paper <a href="https://eprint.iacr.org/2019/877.pdf">”Blind Schnorr 23 Signatures and Signed ElGamal Encryption in the Algebraic Group 24 Model”</a> from 2019 (updated in 2021) introducing Clause Blind Schnorr Signatures 25 is used as theoretical basis for our improvements. The paper explains why simple Blind 26 Schnorr Signatures are broken and how the Clause Schnorr Blind Signature scheme is secured 27 against this attack. 28 </p> 29 <p> 30 Compared to the currently used RSA Blind Signatures, the new scheme has an additional 31 request, two blinding factors instead of one and many calculations are done twice to 32 prevent attacks. 33 </p> 34 <p> 35 The Taler protocols were redesigned to support the Clause Blind Schnorr Signature scheme, 36 including slight alterations to ensure abort-idempotency, and then further specified. 37 Before starting with the implementation of the redesigned protocols, the cryptographic 38 routines for Clause Blind Schnorr Signatures were implemented as part of the thesis. 39 All of the implemented code is tested and benchmarks are added for the cryptographic 40 routines. 41 </p> 42 <p> 43 Multiple results were achieved during this thesis: The redesigned protocols Taler 44 protocols with support for Clause Blind Schnorr Signatures, the implementation of the 45 cryptographic routines, the implementation of Talers core protocols and a detailed comparison 46 between RSA Blind Signatures and Clause Blind Schnorr Signatures. Overall, the Clause 47 Blind Schnorr Signatures are significantly faster, require less disk space, and bandwidth 48 and provide cipher agility for Taler. 49 </p> 50 <h2>Supplemental material</h2> 51 <p> 52 <ul> 53 <li><a href="/pdf/cs-slides.pdf">Defense presentation slides</a></li> 54 <li><a href="/pdf/cs-poster.pdf">Defense poster</a></li> 55 <li><a href="/papers/cs-thesis.pdf">Bachelor's thesis</a></li> 56 </ul> 57 </p> 58 59 {% endblock body_content %}