HTW Berlin Fachbereich 4 Internationaler Studiengang Internationale Medieninformatik (Bachelor) Aktuelle Themen: Cryptography Winter Term 2024/25

Lab 6: Symmetric Key Programming

1. The Java Cryptographic Extension (which implements the Java Cryptographic Architecture) should be in every default Java installation. To check that this is so, and to ensure that the policy files are correct, get the code SimplePolicyTest from Hook, Chapter 1, and run it. Can you do 64 bit encryption? 192? How many bits are you allowed with the default policy?
2. Secret Message
   1. In Chapter 2 of Hook there is a nice example SimpleSymmetricExample. Copy this, compile, run, and report on how it works
   2. Take some paper and make up a key for all the other groups of two in your lab. Don't forget to remember to whom you gave which key! Every group gets their own key, otherwise they can read all your secrets and not just the messages for them!
   3. Adapt SimpleSymmetricExample to encode a different message for each group in the lab. Post a list of these in the Moodle Forum "Secret Message" for this week!
   4. Download the secret messages from the others and decode the messages intended for your group.
   5. Describe any problems that occurred with this exercise!
3. What is the German legal situation today? How many bits may your key be to be used inside of Germany? How many if you want to export it to France? Is anything currently being discussed in France about Crypto? How about exporting to Pakistan, Iraq, Iran, Qatar, or Saudia Arabia? How about your favourite country (if not listed above)?
4. (For the bored) Can you crack any of the messages for which you do not possess a key?

Note that - unless noted otherwise - you work in groups of two! The report is due the evening before your next lecture!