Course of student crypto

Important notice

The current course material exists only in German. As all the CrypTool software is also available in English, we'd be very happy if someone can reuse the material to build a similar course in English for English speaking students and pupils.

Any enhancements to the CrypTool software you might need to do so are welcome too.


The CrypTool student crypto contains two parts, a crypto training exclusively for teachers and the student day. In the crypto training for teachers, the topics cryptography and cryptanalysis are presented in detail and tried out in practice. The focus here is on theory and is intended to give teachers an overview of cryptography so that they can then decide for themselves which parts are suitable for upper school lessons. On the student day, only selected topics will be demonstrated and practically applied. The students should get an overview of the possibilities of cryptography through the lectures. The practical tasks are intended to arouse interest and learn in a playful way using the software CrypTool.

Procedure of the student day
Agent Bob

The student day is divided into lectures and the „agent assignments“, which contain practical tasks to apply the learned methods. The practical tasks include cryptographic puzzles (so-called challenges), and the person who can solve them the fastest will receive a material prize during the event. As prizes there are DVDs/BDs with the films „Enigma“ and „Sneakers“, the books „Not to be cracked“ and „Hidden Messages“ by Klaus Schmeh, the book „Secret Messages“ by Simon Singh as well as the book „Cryptology“ by Albrecht Beutelspacher. The material prizes are provided by the organizing institution. For some of the events books were donated by the book author Klaus Schmeh.

The student days consist of five parts each, three theoretical and two practical ones, in which the students solve the tasks set for them on computers provided.

  • Lecture and Demonstration – Part 1
    • Introduction
      After clarifying the terms cryptology and steganology, CrypTool 1 and CrypTool 2 are presented in a demo. Afterwards, practical applications for today's cryptology will be discussed.
    • Simple encryption
      Using the examples of Scytale and Caesar the transposition and substitution is explained. For both Scytale and Caesar there is a small cryptographic puzzle directly in the lecture, which can be solved with paper and pencil.
    • Improved encryption
      Based on the simple transposition (Skytale) and the simplest substitution (Caesar), the simple column transposition* and the monoalphabetic substitution including the corresponding possibilities of attack are now discussed.

  • Agent assignment – Part 1
    • Basic training as secret agent
      The goal of the basic training is the practical application of the methods just learned with the help of CrypTool 1 or CrypTool 2, for which the students are provided with step-by-step instructions for a total of 6 tasks. Only after the successful completion of all these tasks, the students get their first assignment.
    • Orders 1-2
      The orders are to help Agent 009 to recover the stolen art treasures from the museum and to catch the perpetrators. In the first assignment, a message encrypted with the monoalphabetic substitution is to be broken, and in the second assignment, a Scytale message is to be broken.

  • Lecture and Demonstration – Part 2
    • Automatic encryption
      Here, Enigma as the best known representative of mechanical encryption is explained and demonstrated using CrypTool 1 and 2.
    • Modern encryption (part 1)
      In the modern procedures, the two symmetrical procedures DES and AES* are discussed. Afterwards, both methods are demonstrated in a demo using CrypTool.

  • Lecture and Demonstration – Part 3
    • Modern encryption (part 2)
      In the afternoon, the key exchange according to Diffie-Hellman-Merkle will be demonstrated using a lockable box with two locks. Finally, the RSA procedure and the associated mathematics are explained. In addition to the RSA procedure there is a small puzzle.

  • Agent assignment – Part 2
    • Agent training
      In the agent training, the students are supposed to apply the methods learned in the second and third part of the lecture in practice themselves. For this purpose, the students are provided with step-by-step instructions for a total of 4 tasks. In these tasks, the students should perform a ciphertext-only attack on the Enigma and brute-force attacks on AES (with partially known key). Only after successful completion of all these tasks the students will get their third assignment.
    • Orders 3-4
      In the last two missions, the circle around the perpetrators became more narrow. Thanks to the successful cryptanalysis of the first two orders, the agents are now on the trail of the perpetrators. Whether they are caught or not now depends on whether the last two jobs can be decrypted in time. For job 03, the task is to decipher a message encrypted with Enigma. Even more difficult is job 04, where a hybrid message encrypted with RSA and AES has to be broken.

  • Keywords

* are only briefly mentioned in the context of the presentation, completely available in the documents.

Schedule of the teacher's day

In the crypto training for teachers, the following topics are discussed and partly applied in practice using CrypTool.

  • Introduction
    First, the terms of cryptology and steganology are clarified. Afterwards, the software CrypTool 1 and CrypTool 2 will be demonstrated in a demo. This is followed by an outline of the history of the development of cryptology from 1900 BC to the present.
  • Encryption by hand
    Simple manual procedures of cryptography are demonstrated and practically tested. The following procedures are presented: Skytale, Caesar, Simple Column Transposition, Monoalphabetic Substitution, Homophonic Method*, the Vigenère Method* and One-Time-Pads.
  • encryption machines
    As the best known encryption engine the Enigma is presented here. The cryptoanalysis, i.e. the breaking of Enigma codes, is also discussed. Finally, other machines* are briefly introduced: SIGABA, SIGCUM, TypeX, Purple, Lorenz machine, secret writer T52.
  • Computer encryption
    Here the currently used and applied algorithms of modern symmetric cryptography and asymmetric cryptography are presented. As representatives of symmetric cryptography DES and AES* are explained and demonstrated in practice. The transition from symmetric to asymmetric cryptography is explained – just like in the story itself – using the Diffie-Hellman-Merkle method for key exchange. Then the mathematical basics and the asymmetric RSA method – today one of the most frequently used methods worldwide – are discussed in detail.
  • Outlook/Future: Quantum Cryptography
    Finally, a short outlook into the future, namely quantum cryptography*, is given. Wiesner's quantum money from the 70s is presented, which can be seen today as the origin of quantum cryptography. Also the BB84 method used today is briefly discussed*. Furthermore, the potential of cryptanalysis using the quantum computer is discussed at the end.

* are only briefly mentioned in the context of the presentation, completely available in the documents.


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