Cryptanalysis (SS 2021)

Content

Cryptanalytic attacks define the security of cryptographic algorithms, and understanding them is crucial to understand cryptographic design. This lecture aims to give you some in-depth knowledge of several recent state-of-the-art topics in cryptography, with a focus on cryptanalysis:

• Classic and quantum algorithms for factoring and discrete log
• Cryptanalysis of block ciphers (differential, linear, algebraic)
• Cryptanalysis of hash functions and stream ciphers
• Lattices and continued fractions in cryptanalysis

In the exercises, you will implement some of these attacks to solve cryptanalytic challenges. In the seminar, additional selected topics may be presented by participants -- see below for a list of suggested topics. This course is equivalent to the previous course “Applied Cryptography 2” (SS 2020).

Material

Lecture and Seminar

Date	Who	Topic	Video
04.03.2021	ME	L1 – Factoring and Continued Fractions	YouTube
11.03.2021	ME	L2 – Discrete Logarithm	YouTube
18.03.2021	MS	L3 – Quantum Cryptanalysis	YouTube
25.03.2021	ME	L4 – Lattices	YouTube
15.04.2021	MS	L5 – TLS security & Protocol Attacks	YouTube
22.04.2021	ME	L6 – Differential Cryptanalysis	YouTube
29.04.2021	MS	L7 – Advanced Differential Attacks	YouTube
06.05.2021	ME	L8 – Linear Cryptanalysis	YouTube
20.05.2021	MS	L9 – Sponges & Stream Ciphers	YouTube
27.05.2021	MS	L10 – Algebraic Attacks	YouTube
10.06.2021	--	no lecture	--
17.06.2021	T4	S1 – Code-based PQ Crypto	WebEx
24.06.2021	T7	S2 – Security of Password Hashing	WebEx
01.07.2021		VO Exam (oral, first date)	Discord

All videos are listed in the YouTube playlist.

Exercises

Date	Topic	Where
18.03.2021	Team registration deadline	STicS
18.03.2021	T1 – Asymmetric Cryptanalysis	After L3
22.04.2021	T1 – Question session	After L6
29.04.2021	T1 – Submission deadline (23:59)	STicS
11.05.2021	T1 – Assignment interviews (individual slots)	Discord
06.05.2021	T2 – Symmetric Cryptanalysis (figures)	After L8
27.05.2021	T2 – Question session
10.06.2021	T2 – Submission deadline (23:59)	STicS

We're available for individual KU questions after each lecture on Discord.

Administrative Information

Exercises (KU)

In the exercises, you implement cryptanalysis techniques from the lecture in teams of 2. To get a grade, you submit your implementations for 2 assignments, which we will discuss with you in a final interview ("Abgabegespräch"). Use the Student Tick System (STicS) to register your team and upload your submissions. We usually won't need the 16:30–17:15 KU timeslots (except for question times and seminar presentations).

Lecture exams and seminar talks (VO)

There are 2 ways to get a grade for the VO:

• Exam mode: Write exam at the end of the term or take an oral exam later

  • You can find the exam dates and registration in TUGRAZonline.

• Seminar mode: Participate actively in KU+VO and give a seminar presentation in one of the last lectures (45 minutes), for example on

  • Block Ciphers: Division Property
  • Block Ciphers: Zero-Correlation and Multidimensional Linear Cryptanalysis
  • Block Ciphers: MitM and Biclique Attacks
  • Hash Functions: Rebound Attack
  • Hash Functions: Cryptanalytic Exploits (MD5 Certificates etc.)
  • Authenticated Encryption: Security Proofs and Robustness
  • Algebraic Attacks: Gröbner Basis, etc.
  • RSA: (In)Security in Practice
  • Elliptic-Curve Cryptography: Secure Curves
  • Post-Quantum: Lattices and Learning with errors
  • Post-Quantum: Coding-based Cryptography
  • Selected Topics: Implementation Security and Masking
  • Selected Topics: Statistical Ineffective Fault Attacks
  • Selected Topics: Backdoors in Cryptography
  • Selected Topics: Security of Password Hashing

COVID-19 Info

All lectures and exercises are conducted virtually this year. The lectures are streamed live on Youtube (URLs below and in your calendar). For most contents, recordings will be available afterwards. Video meetings for exercise interviews and question sessions are on Discord, where you can also ask written questions at any time. For the optional seminar talk, you will have the choice between online and live presentations if conditions permit. The alternative is a virtual oral lecture exam.

Literature

The lecture slides are reasonably self-contained, but often briefly phrased. If you prefer full-text resources, you may find some of the following books interesting:

• The Block Cipher Companion, by L.R. Knudsen and M.J.B. Robshaw
• An Introduction to Mathematical Cryptography, by J. Hoffstein, J. Pipher, and J.H. Silverman

Lecturers