In the particular case of a series of n equally-probably, independent events, the entropy is given as H = - log 1/n, measured in bits. For example, the entropy of a fair die is - log 1/6 = 2.58 bits per throw.
In this case, the random event is words chosen from a word list. Four words are chosen from fifty thousand, with each word having equal probability of being chosen. So the entropy (measure of randomness) is - log 1/50,000 = 15.6 bits per word, or 62.4 bits per four-word combination. (The script also adds random numbers or symbols, to add up to 90 bits.)
http://www.amazon.com/Introduction-Information-Theory-Symbol...
In the particular case of a series of n equally-probably, independent events, the entropy is given as H = - log 1/n, measured in bits. For example, the entropy of a fair die is - log 1/6 = 2.58 bits per throw.
In this case, the random event is words chosen from a word list. Four words are chosen from fifty thousand, with each word having equal probability of being chosen. So the entropy (measure of randomness) is - log 1/50,000 = 15.6 bits per word, or 62.4 bits per four-word combination. (The script also adds random numbers or symbols, to add up to 90 bits.)