Automated Frequency Analysis

Read this:

Then decrypt this: "Iuhtxhqfb dqdobvlv lv wkh vwxgb ri wkh glvwulexwlrq ri wkh ohwwhuv lq d whaw. Dqdobvlv ri iuhtxhqflhv khos ghfubswlqj vxevwlwxwlrq-edvhg flskhuv xvlqj wkh idfw wkdw vrph ohwwhuv dssdulwlrqv duh ydublqj lq d jlyhq odqjxdjh : lq hqjolvk, ohwwhuv H, W ru D duh frpprq zkloh C ru T duh uduh."

Most automated cryptography tools use this sort of technique behind the scenes.

Another example is the chi-squared statistic:

Crypto has a lot of math, but luckily, because it is math, someone else has usually written a tool to do it for you. It takes a lot of work to get to the cutting edge in this field.

  1. What is text fitness?
  2. Explain how frequency analysis can be used to automatically detect the correct decryption of a ciphertext.
  3. What is leet speak?
  4. How would this break a text fitness calculation?