Instructions

#Homework 04

This assignment involves calculating entropy of passwords.

##Password Entropy

Entropy is a measure of how hard it would be to guess a password. There are several ways of calculating entropy. The different methods tend to give slightly different numbers, but Entropy is really just an estimate. The formula we will use is probably not the best formula, but it is straightforward and serves our purposes.

###E = log2(R(L-1))

where
E is an integer representing the maximum entropy. (Truncate the decimal part; don't round)
R is the range of the characters.
    range is 26 if only lower case letters are used
    range is 52 if upper and lower case letters are used
    range is 62 if upper, lower, and digits are used.
    range is 67 if upper, lower, digits, and 5 special characters are used.
    range is 72 if upper, lower, digits, and 10 special characters are used.
####Range To calculate range, set range to 0

Add 26 if there is 1 or more upper case characters
Add 26 if there is 1 or more lower case characters
Add 10 if there is 1 or more digits (0 through 9)
Add 1 for each special character in the set "`~!@#$%^&*()-_=+[{]}|;:'",<.>/?</.>" If a character occurs more than once, it is only counted 1 time.
###Log2

Java does not have a built-in method for logs in base 2. However, you may calculate a base 2 log by using the following formula.

double result = Math.log(number) / Math.log(2));
You will need to do some unit tests on your log2(number) method. Here are some useful values. You may use a calculator to get some additional values to test. You should have at least 20 values tested in the log2() test.

Log2(1) is 0.000000
Log2(2) is 1.000000
Log2(3) is 1.584963
Log2(4) is 2.000000
Log2(5) is 2.321928
Log2(16) is ________ (You should be able to figure this out)
Log2(0) is -Infinity
Log2(-1) is NaN (Not a number)
Log2(.5) is -1
Log2(.25)is -2
Log2(0.12345) is-3.01800125841
Log2(45.3) is 5.50143914516
##Running Tests

There are currently a couple of unit tests written for you. However, the tests will fail. When a test fails the error is usually in the code, but it can be in the test. In this case I am telling you up front that the errors are in the tests.

First, run the existing tests and correct them.
Complete the missing parts of the main class.  You will have to complete and write several methods.
Write test cases for all methods that return a value.  Run those tests.  Generally you should have approximately 20 tests per method.  Be sure you are checking all possible values (negative, zero, positive, fractions, etc).  Get all of the tests running correctly.
Zip your file and turn it in.