The somewhat dimly lit, but not quite dark arts.
Due before class, Friday 21 Sep 2006
I'm trying to find out about a system to electronically submit things instead of emailing them to me. Watch this space for details.
You should look over these questions and answer them, but you do not need to turn them in: Pfleeger 2.13, 2.16, 2.17, 2.22, 2.24, 2.26, 2.29, 2.31.
Decrypt the following ciphertext files. The plaintext files are all 7-bit ASCII text files with English text.
For each, you should submit the plaintext and the key. You may use software that assists, but doesn't automate, the solution of the ciphers. (For example, Professor Salter's Krypto tool) However, you must document the software you used along with the source of same. Any software you write yourself should be submitted via the handin program.
It is possible to solve some of these by hand, however, I want you to write up the methodology you used to get to the solution, including brief descriptions of failed attempts. I will give substantial partial credit for a good method that might not have reached a solution. Note that I do not expect you to be able to solve all of these! For those that you do not solve, describe what you know about the cipher at that point (results of tests performed, possible cipher used, possible key length, probable words, etc.).
If hints are needed, let me know.
This next ciphertext is encrypted using 128 bit AES. The file aes.cipher is a binary file encrypted with 128 bit key, of which the first 24 bits change and the remainder are all set to 0. The command line tool supplied in this tar file aes.tgz will probably prove to be quite useful. (modified from source from Ethan Miller@UCSC modified from implementation by Philip J. Erdelsky)
Keep in mind, that you don't necessarily have to go through the entire file when trying a key, and you can save some calculation in this manner.
This software operates in CBC mode with an IV of 0. You can use any language to solve this problem, although this particular program is in C. Keep in mind that a brute force solution may take a while to run, so do not put it off until the last minute.
Your textbook has some description of techniques that can be used to identify and break these ciphers. You can also look at the Military Field Manual on Basic Cryptanalysis for other suggestions. (I'll bring in my printed version of it into the CS Office.)