Entropy, as it relates to passwords, is a measure of how many attempts it will take during a search to exhaust all possibilities of your password. Pscalc is a utility to quickly let you calculate the entropy of a password given a few bits of information.

Installation

Install Perl, and then grab the code from https://github.com/hadenpike/pscalc.git. Make sure the script is in your PATH:

export PATH="/path/to/pscalc/:${PATH}"

in Bash, for example. Documentation for this script follows.

NAME

pscalc — Determine entropy of a password

SYNOPSIS

$ pscalc [size_of_alphabet] [password_size]

DESCRIPTION

The entropy of a password is determined by: log(alphabet_size)/log(2) where alphabet_size is equal to the sum of the allowed characters (95 for lowercase, uppercase, digits, and the 33 special characters), and n is the length of the password.

EXAMPLE

Assume we are using the standard alphabet size (95), and we have a twelve character password. Using this tool:

$ pscalc 95 12
78.84

Thus it would take 2^79 = 6.04462909807315e+23 attempts to try all possibilities. Consider the speed of computers and increase the numbers passed to pscalc, and you’ll see that’s not actually a great result.

REFERENCE

Thanks to Steve Gibson https://www.grc.com/ for pointing this formula out on the Security Now podcast https://twit.tv/sn.