Capture the Flag Exercise 1 - FAQ
- Q: How to set an environment on DeterLab for testing?
A: Allocate three machines - one client, one server, one router
connected to the client and to the server. Have client and server send
any traffic to each other - e.g., run ping on one of them. On the
router, use nfqueue to capture traffic.
- Q: Are we supposed to use the
same key for every message if using homophonic cipher method? Since
the letter frequency is different for each message.
A: Homophonic cipher uses letter frequency in spoken language
to set up set sizes, not frequency in actual messages. So there is
just one key. The message letter frequency may or may not fit the one
you anticipated but that's OK. Attackers looking to break the cipher
must work off the frequency tables for spoken language too.
- Q: Can we encode same messages differently?
A: If you end up using polygram cipher you can use CBC mode for it to
make same messages appear differently. But in any case you have to use
the same key for every message, and the same encryption method.
- Q:Should our encrypted messages be only in ASCII?
A: No, they can be in binary too. Input messages are ASCII only, as
specified in the exercise description.
- Q: For the monoalphabetic cipher, can we calculate a mapping scheme
based on each individual message? Or does this count as a
A: No, you must use one mapping for every message.
- Q: Is the key only going to be used for stream ciphers?
A: That depends on your implementation but yes, key is likely only
going to be used in stream cipher.
- Q: When implementing stream cipher, do we have to do the bit
XOR implementation or can I just generate a huge random number and add
each corresponding digit to the ascii code for the letter of the
message I am trying to encrypt?
A: You can do either