A password generator inspired by XKCD #936

passphrase.lhs

#!/usr/bin/env runhaskell

A password generator inspired by XKCD #936: http://xkcd.com/936/

Passwords which are easy for humans to remeber and hard for computers to guess.

> import Control.Monad (liftM, when)
> import Data.List (intercalate, isPrefixOf)
> import System.Random (getStdGen, randomRs)
> import System.Environment (getArgs)
> import System.Exit (exitWith, ExitCode(..))

> dict_file = "/usr/share/dict/words"
> default_words = "4"

> usage= "Usage: passphrase.lhs [-v|--verbose] " ++
>        "[word_count (default=" ++ default_words ++ ")]"

> main = do
>   args <- getArgs
>   when ("-h" `elem` args || "--help" `elem` args) $ do
>       putStrLn usage
>       exitWith ExitSuccess
>   let args' = filter (not . ("-" `isPrefixOf`)) args
>   let n = read . head $ args' ++ [default_words]
>   dict <- (filter (not.null) . lines) `liftM` readFile dict_file
>   let dsize = length dict
>   ixs <- (take n . randomRs (0, dsize-1)) `liftM` getStdGen
>   putStr $ intercalate " " . map (dict!!) $ ixs
>   when ("-v" `elem` args || "--verbose" `elem` args) $ do
>     let bits = logBase 2 ((fromIntegral dsize)^n)
>     putStrLn ""
>     putStrLn $ show (round bits) ++ " bits of entropy"